A PUBLICATION ON LIGHTING, ELECTRONICS, X-RAY AND OTHER TECHNICAL SUBJECTS

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP83-00423R002000130013-1
• Release Decision: RIPPUB
• Original Classification: K
• Document Page Count: 52
• Document Creation Date: November 9, 2016
• Document Release Date: February 22, 1999
• Sequence Number: 13
• Publication Date: August 1, 1952
• Content Type: PERRPT

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PHILIPS TECHNICAL
REVIEW
A publication on Lighting, Electronics,
X-Ray and other technical subjects
PHILIPS
PHILIPS RESEARCH LABORATORIES
'Philips Techn. Rev. Vol. 13, No. 1-2, pp. 1-48
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PHILIPS PUBLICATIONS
Philips Technical Review
A monthly publication dealing with technical problems relating to the
products, processes and investigations of the Philips Industries. It contains
articles on Lighting, Electronics, X-Ray and other technical subjects.
32 pages per issue, size 201/2 X 291/2 cm.
Published in English, French, German and Dutch.
Philips Research Reports
A publication containing physical, chemical and technical papers in the
English and French languages, relating to the theoretical and experimental
research work carried out in the various Philips Laboratories. Philips Research
Reports are published in volumes of six issues, each of about 80 pages, size
151/2 X 231/2 cm.
Communication News
A quarterly publication on transmitters, transmitting valves, line telephony,
line telegraphy and automatic telephony. 32 pages per :issue, size
201/2 X 291/2 cm. Published only in the English language.
For particulars regarding these publications apply to the publishers
mentioned on the back cover of this issue.
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VOL. 13 No. 1-2, pp. 1-48
PhIis Technical Review
DEALING WITH TECHNICAL PROBLEMS
RELATING TO THE PRODUCTS, PROCESSES AND INVESTIGATIONS OF
THE PHILIPS INDUSTRIES
EDITED BY THE RESEARCH LABORATORY OF N.V. PHILIPS' GLOEILAMPENFABRIEKEN,EINDHOVEN, NETHERLANDS
PHILIPS' DIAMOND JUBILEE
It was sixty years ago, in the month of May, that the Philips' Lamp Works were
established at Eindhoven. The Editors of Philips' Technical Review wish to take
part in celebrating this memorable event by issuing this Jubilee Edition. In. the
1941 volume of this Journal one might seek in vain for any mention of the commem-
moration of-the 50th year of our Concern's existence. Under the conditions of enemy
occupation it had been decided merely to celebrate that event unostentatiously at a
meeting of the Management and the executives. Nevertheless that day in May 1941
turned out to be one of boisterous merry-making. Quite unexpectedly the tens of
thousands of Philips workers spontaneously downed tools and set out in procession to
give vent to their feelings of joy - and to their sense of national pride. Within a few
hours almost the entire population of Eindhoven had enthusiastically joined in that
demonstration. Although these festivities were abruptly brought to an end by the
threat of armed intervention and prohibitions, there are many who regard that May
day of 1941 as one of the most memorable days of their lives. Now that, on the occasion
of this Diamond Jubilee, liberty and fraternity again reign supreme in our country,
there is every inducement for celebration when looking back upon the past, as
we shall do in this Jubilee issue. No attempt will be made here to set forth the history of
the Philips' concern: as a whole ; this is to be done in some other way. It has been deemed
Spontaneous jubilation on the 50th anniversary of the foundation of the Philips' Works.
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best Lo confine the scope
of this special issue to some
aspects of the research work
which, from about 1910 on-
wards, has been carried out
mainly in the Physical Research
Laboratory, and to throw light
upon the importance of that
work for the enterprises of our
Concern. Dr. W. de Groot,
who has been connected with
the laboratory ever since 1923
and thus has been personally as-
sociated with the development
of this research work for the
greater part, having himself
furnished valuable contribu-
tions towards it, was found pre-
pared to write a review on the
lines indicated above. It will not lay any claim to being a complete summing up of
all research work carried out - such might well prove to be too dry reading -
but rather it is to be regarded as an illustrated story about the laboratory, showing
in particular the multifarious nature of the problems dealt with and the often
unexpected new possibilities emanating therefrom.
In conclusion, on behalf of the whole of the editorial staff, we extend our sincere
congratulations, on this Diamond Jubilee, to Dr. A. F. Philips, one of the two foun-
ders of the Concern, and further Lo the Board of Management and to all who have
worked so hard to contribute towards the growth and prosperity of Philips Industries.
TIIE EDITORS
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SCIENTIFIC RESEARCH OF PHILIPS' INDUSTRIES
FROM 1891 TO 1951
With the invention, at the beginning of the wise greatly interested in electric light. Later on
nineteenth century, of the voltaic pile and the he conducted negotations for Rathenau in Berlin
galvanic battery, providing a source of current between the A.E.G. and the municipality of Amster-
with an almost unlimited voltage and a relatively dam about an electric-lighting project, but these
small internal resistance, in principle also the negotiations broke down on account of the high price
possibility of electric light was created. In 1808 per kWh (fl. 0.60) asked for by the A.E.G.
Davy succeeded in passing current through air in 1890, when 6800 are lamps and 118,000
between two carbon rods of a few millimetres incandescent lamps were already burning in Paris,
diameter. The tips of the carbons and the gas four electric power stations in Berlin were supplying
discharge radiated a bright light. Upon the carbon current to some 3000 are lamps and 70,000 in-
tips being spaced a couple of centimetres apart, candescent lamps, and in London a generating
owing to convection the discharge assumed the station was being built for feeding 600,000 lamps of
shape of an are (an inverted U), which name came 10 candle power, whilst in the U.S.A. 23,500 arc
to be used to describe all gas discharges with a lamps and 2,800,000 incandescent lamps had already
high current density and with a thermionic cathode. been installed, Ir. Philips conceived the idea of
In a certain sense the carbon arc is the precursor starting a new incandescent-lamp factory in the
of modern discharge lamps and, in so far as the Netherlands, where others had already been
light originates from the glowing carbon tips, also established, among which were the Pope and the
of the incandescent lamp. A second forerunner of the De Kothinski works. This plan materialised in the
incandescent lamp is the platinum wire brought to month of May 1891 with the opening of the factory at
incandescence by an electric current, an experiment Eindhoven. In the course of time G. L. F. P hil i p s
which was also carried out by Davy (1802). Carbon- and his younger brother Anton Frederik Philips,
are lamps were known about 1850 and, as was sub- who joined the firm in 1895, turned this small
sequently disclosed in the famous law-suit between factory, with a starting capital of 75,000 guilders,
Edison and Goebel (1893), also electric incandescent into a world-wide concern, the parallel of which
lamps had already been made at that time. These is but scarcely found.
sources of light were fed from galvanic batteries. It It is not the intention to enter here into the history
was not, however, until the invention of the dynamo of this concern, for this will be found in a book
(Siemens 1866, Gramme 1869) that electric light which is to be published shortly. Instead of that,
came to be introduced on any large scale. In 1879, a review will be given of the development of the
on the one hand the differential-arc lamp of Von scientific research, both in the pure and in the
Hefner-Alteneck made its appearance and, on the applied sciences, of the Philips Industries and in
other hand, Edison's carbon-filament lamp, which particular that which has been carried out in the
was demonstrated at the Paris exhibition of 1881, Physical Research Laboratory founded in 1914.
together with the machines for generating the
current and the means of distributing it. That The first research work connected with the Philips
exhibition aroused interest everywhere, and it business was carried out by Gerard Philips
was shortly after this that E. Rathenau founded himself. For some time before the factory was started
the A.E.G. in Germany. he was studying the preparation of the carbon
All this greatly interested the young Dutchman filament and various other processes in a primitive
Gerard Leonard Frederik Philips, born 9th workshop at home. In November 1890, when writing
October 1858 at Zaltbommel, who was studying to one of the many people with whom he was
at the Polytechnical School (now the Technical negotiating for the establishing of the new factory,
University) at Delft, where he graduated as an Ir. Philips wrote: "I am able to produce perfectly
engineer in 1883. Shortly after that he was given homogeneous cellulose filaments on a business
the opportunity to install electric lighting in some scale". Considering, however, what the management
ships at Glasgow, and there he made the acquaintance of a rapidly growing young industry involved, and
of William Thomson (Lord Kelvin), who was like- bearing in mind that up to 1895 both the commer-
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4 PHILIPS TECIINICM, REV'IEW' VOL. 13, No. 1-2
Ir. G. L. F. Philips engaged with his first experiments for
the manufacture of carbon flanients from cellulose (1890).
cial side of the business and Lite management of the
works were in the hands of one man, obviously this
research work was at first limited to what was
absolutely essential. Technical and scientific help
soon became necessary, especially when from 1903
onwards new materials, such as osmium, tantalum
and tungsten, the last of which was destined to be the
filament material of the future, came to be used in
the manufacture of incandescent lamps. About 1907,
at the time that incandescent lamps began to be
made with squirted tungsten wire, P. N. L. Staa1,
A. de Broekert and II. Gooskens*) joined the
firm as Gerard Philips's assistants, these being
followed, respectively in 1908 and 1909, by the
chemical engineers J.C.Lokker and A.dc Graaff,
and shortly afterwards by the mechanical engineers
IT. de Jong, 11. Ileufel and W. K.oning.
In December 1911 the brittle squirted wire was
successfully replaced by the more rigid drawn wire.
Thus a technical staff of some size was formed,
comprising people trained in mechanics and in
chemistry, but-it was not long before also the
*) lit this review the names of people connected with the
Philips Concern are spaced out, while those of others are
printed in italics.
iteed of physicists began to be felt when, in 1913,
a new development was announced in Lite lamp-
making world, in the form of the gas-filled lamp.
In Lite General Electric Company's laboratory at
Schenectady (U.S.A.), where Edisoii's work was
carried on and physicists were available, in 1909
Coolidge had found an entirely new method for
drawing strong, thin wires of tungsten. There
soon followed, in 1913, in the same laboratory,
1. Langinuir's invention whereby a coiled filament
Could be brought to incandescence in an inert-gas
atmosphere, thereby counteracting vaporization
of the tungsten and thus making it possible to
heat Lite filament to a higher temperature, so that
the luminous output of the lamps could be greatly
increased. Within a very short space of time a num-
ber of other inventions followed from the same
laboratory, such as X-ray tubes with heated cathode
and gas-filled rectifying tubes.
In November 1913 also Philips brought gas-
filled tungsten lamps on the market, under the name
of "half-watt lamps". In Lite manufacture of these
lamps and also, for instance, in their photometry so
many problems arose which lay- more in the domain
of physics than in that of chemistry or mechanics
that I r. Philips decided to engage a physicist. Thus
on 2nd January 1914 G. I b i s t joined the firm in
that capacity, and this was the beginning of the
Prof. Dr. G. IIolst, after a painting by S. Schroder.
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foundation of a physical laboratory. Some months
later E. Oosterhuis joined the staff of this
laboratory as second physicist.
It will be shown how the work of the laboratory
established in 1914, starting withthe problems of the
manufacture of incandescent lamps, has expanded
into such a multifarious programme, from which
such a wide variety of other products have been
born. In this growth three main periods are to be
distinguished:
1) 1914-1923, the period which saw the first world
war and during which the laboratory was
located in a part of the lamp factory;
2) 1923-1940, beginning with the opening of
a new laboratory specially equipped for the
purpose (in 1929 it was considerably enlarged)
and ending with the occupation of the Nether-
lands by enemy forces in the second world war;
3) 1940 up to the present day, covering the years
of occupation and the revival of activity after
the country's liberation.
After studying at the Technical University at
Zurich- where he took his doctor's degree in 1914 -
Dr. Holst worked for a number of years in the
laboratory of If. Kamerlingh Onnes at Leyden,
where, inter ilia, he took an active part in the
discovery of superconductivity. Thus, in addition
to his bent for purely scientific work, Dr. hoist
was also technically interested in taking up his
new appointment with the Philips' laboratory.
Although it was considered as his main task to
study the physical questions arising in the manu-
facture of' the tungsten lamp, it was felt at the same
time that it should not be left at that, but that it
was necessary to penetrate to the very roots of the
phenomena to be studied. From the tackling of
subjects on such a wider basis physical science
was primarily benefited, but then this in turn bore
fruit for technical science, often in a surprising
manner, in the form of improvements of existing
products and the opening up of new fields of activity.
The study of the tungsten lamp was therefore
the starting point: first the behaviour of tungsten
wire in the processing, and further its behaviour
upon being heated by an electric current to a high
temperature in a glass bulb either in vacuo
or in the atmosphere of an inert gas; the
current had to be passed into the bulb via vacuum-
tight and. fused-in wires.
Owing to the extensive programme of work the
staff soon had to be enlarged. Dr. Hoist received
successively the assistance of P. G. Cath, S. Weber,
C. Bol, II. C. Burger, C Hertz, Balth. van
der Pol, A. Bou.wers, A. E. van Arkel, W. Gciss,
J. H. de Boer, P. Clausing, B. Vermeulen,
W. de Groot, C. Zwikkcr and others, whilst
contributions towards this research were likewise
furnished by L. Hamburger, D.
J. A. M. van Liemp t, who belonged
chemical staff of the works.
Lely and
to the
As regards the physical problems directly
related to the incandescent lamp, first of all there
was the photometry to be studied, particularly
of the gas-filled lamps, since their luminous flux
is distributed in space in a less surveyable manner
than that of vacuum lamps with a linear filament.
In a series of "Communications of the Philips'
Laboratory" (1918-1919), which in
be regarded as the forerunners of
a sense may
this journal,
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conception- ill Ihl' find of ill it tit illation wira
explaitu'd 1(11(1 tu' ba-it'I('ntint- (If utility light
fitLing-. projector-- gar lit Ili ll- uill igi(t lautp-.
('te. wee(' d('alt \41111.
Of it room hi rid it rnerttal nature 441(- 1114' in4 c - t i-
git lioit of rit (liit tittrl. -11 ('11 a- lit, spl-cl rat
encrgv di-trihotinn of int?aud('-rant litmlt At that
title 11(1nclr".S formula 4t a- -till regardctl with
Soule -erptici-4'n and IIll-r(? 44 a- no I houl111( bit451cii Boll r'- tlworv and the lrhenomena
of ('lcctrit rnndit ctit it ce iu g1(-e-, fur 4%Itich. in 19?6.
tiler 44cr- both awarded 1114' \obt'1 prize. hertz' -
ins I'-1 tiun- t4' ill Ito, disci--ed iit ill' next section.
'Ha' nth-t intlturtit rtt re - IIIIuf* the itt4.c-ligation
of gas di-charge- ill Ibe period I O 11- I )2.) w1(- till'
dlepur insight I11err'bv gained into the plicnonlena
of cIteIll 'a! hrait kii iwn. in particular at
loot pre-sure. ill Jul r e g 1(- r- between plane,
parallel. cold metallic electrode and the deeper
kno4tlydge gained of tine Irann-itiun from tit, non-
-elf--u-taiue(l to the -elf--u,tained di-charge
(Ilol-I. ()u-lirhui-), ()Ic if' the fact.- tlu'reb4-
r-tit bli-hell 44it- that, t11e production of electrons
in the al0w i- due to tu' action of tlic positive
roll- upon Lhe cathode and 110E a' TOIrnsen(1
itnaginetl it to he. a- it result of direct. ionization
of till' g1(- 11 111v pusibyl' run-.
Tlit fir-t practical ultruute of the in4r-t.igation
into gin- di-r11arge- \N ii- the appearance in this
period of the Ill lilt glo4% Iantp (IOI") and the
tong - lr?n a rc 11(1111) 44iIIt noun - billing ( 1920).
'I'll(- Int l- Ligation of rare -a-c- was facilitated
114 tin' fact that -ince I01(t the Philip-- works
load 1wrii ntakilg (under Lhe gltidartee of II. Ii Ii ppo)
I lair o5t It 111111 d U).4 gi it and nitrogen. l'roin which
the rare g1(-e- could be di-tilled.
litr during t(1( 441(4' Ill' importation of' X-ray
I-(the- Kit- -lopped medical pract.itioner., ill tit(,
Nederland-cot their tube- to the Philip works
Fur repair. I'bn- intern-t al-o canto to be taken
in the tuhr-. not ullIv ill 4'r-pact to the gas-filled
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tubes that were then being used but also in the new
Coolidge vacuum X-ray tube with a heated
tungsten filament as electron source.
The study of the manner in which the metal
leads could be passed through the glass of the
lamp bulb led to the production of ferrochrom-
ium alloys which have about the same coeffi-
cient of thermal expansion as that of glass and
which can be fused onto glass. Prior to this, the
leads were of platinum wire, later of iron wire
coated with copper; for other glass-metal joints
pure copper was used, which differs in expansion
from glass but owing to its softness changes shape
while cooling. With the new alloys (B o 1, B o u w e r s,
B. Jonas) there was no need to make _ allowance
for any deformation during cooling, so that the
leads and connections could be made much stronger
and fusing-in was no longer confined to thin-walled
tubes. This led to the construction of metal trans-
mitting tubes and metal X-ray tubes. In connection
therewith it was of importance that in 1916 Philips
had started a glass works of their own (P. J.
Schoonenberg).
In 1883 Edison had discovered that an electric
current flowed through the vacuum between the
poles of the filament in his incandescent lamps,
a fact which we now know to be caused by electron
emission. Following upon Richardson's investigation
of electron emission, in 1904 Fleming had invented
the diode and in 1907 Lee de Forest had made the
first triodes by adding a grid. Simple receiving
triodes were produced by Philips in 1917, these
being followed by transmitting triodes and
diodes for rectifying alternating currents. Soon a
systematic study of the phenomena in the radio
valve was started. In 1922 Balth. van der Pol
(a former pupil of H. A. Lorentz) was charged with
radio research*).
The new laboratory, situated in a part of Eind-
hoven which in 1923 was still on the outskirts of the
town, was taken into occupation in November that
year by a staff of 15 graduated physicists, chemists
and engineers with about 20 assistants, instrument-
makers, glass-blowers, etc. By 1939 there were 106
scientists and 360 assistants. The number of publi-
cations issued by the laboratory in the period 1914-
Since 1949 Prof. Dr. Balth. van der Pol has been
Director of the Comite Consultatif International des Radio-
communications at Geneva.
In connection with the manufacture of radio
valves, whereby use was made of the electron-
emitting properties of tungsten, further investi-
gations were carried out with a view to finding
materials which could replace tungsten and give a
greater emission for a smaller filament power.
In 1921, as a result of new ideas about the theory
of atoms, Coster and.Hevesy discovered the element
hafnium, related to zirconium. Great expectations
were held about the thermionic emission of this ele-
ment, and the preparation and study of this new
material was energetically taken in hand in the
Philips' laboratory. Though this did not culminate
in the important results that were expected of it,
the chemical and metallurgical experience thereby
gained was useful in many respects.
The ever-increasing amount of research work to
be carried out demanded more space, so that in
1922 it was decided to build a new laboratory,
which was completed and taken into use in 1923.
Memorial tablet in the hall of the Research Laboratory pre-
sented to Jr. G. L. F. Philips on the occasion of his 50th
anniversary as Engineer in 1933.
On 1st April 1922 Dr. In G. Philips, who during
the first world war had had the honorary degree of
doctor in the technical sciences conferred upon
him at Delft, resigned his co-directorship at the age
of 63. He died at The Hague on 26th January 1942.
1923 was about 150 and in the period 1923 - 1940
about 1500. A review of research done in this latter
period must therefore be limited to the main lines
and some outstanding points.
The work begun in the old laboratory was contin-
ued in the new under more favourable circumstan-
ces. With the larger space available and the increase
of staff there was more opportunity for deeper
and more far-reaching investigations. It should be
mentioned that Dr. H o l s t always left his scientific
staff a high degree of freedom.
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 It is impossible, in this short survey, to give a
proper account of the various ways in which
Dr. IlolsL stimulated his many co-workers. The
few places where Ilolst is explicitly named here,
certainly give an imperfect impression in this
respect. The same applies to I)r. Oosterhuis,
who (until 19=16) held the position of Vice-Director
and supervised a team of workers engaged in prac-
tical radio research.
Of course research work was still bound to a cer-
tain extent to the factories and their production.
The laboratory was expected not only to evolve new
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ideas leading to new products or to the improve-
nicnt of existing ones - ideas which were suitable
for patenting - but these ideas had also to be
brought to fruition for manufacture. Further, a
certain amount of service was called for, such as the
calibrating of measuring instruments, examination
and testing of materials, etc. Thus, side by side
with the purely scientific work, more and more work
of it different nature had to be done. This is the
reason why the number of publications issued year
by year did not grow in proportion to the growth
of the staff.
For a better comprehension of [lie vastness of the
laboratory work this has been divided into five main
groups. viz:
1. Light and the production of light, including
gas discharges.
11. I lrctroteehnics and radio, including acoustics.
Ili. Chemistry, including metallurgy.
IV. X-ray investigations.
V. 'klatbetnaties and mathematical physics.
These amain divisions have to be taken broadly,
and furthertrtore there are important connections
between them. The X-ray examination of crystals,
for instance, forms it link between the groups III
and IN', the examination of magnetic materials links
up groups II and III, whilst the problems coming
under the heading V mostly_ arise from other groups,
especially from group II.
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JULY-AUGUST 1951 1891-1951.
I. Light and gas discharges
Investigations in connection with incandescent
lamps, as far as the new laboratory is concerned,
were more or less terminated about 1925 by
Zwikker's thesis on the physical properties of
tungsten as functions of temperature, which work
can be placed side by side with similar work in the
U.S.A. In the lamp factory, where a physicochem-
ical laboratory continued to be maintained, for
many years much important work was done by
Van Liempt, Geiss and others in the field of the
chemistry of tungsten compounds and the metal-
lurgy of tungsten.
appeared that an are discharge can take place in a
rare gas when there is a potential diflerencc between
anode and cathode lower than the lowest excitation
potential. Other investigations concerned the n e g a-
tive glow discharge, especially the heating of
the anode when electrons enter it, and the thermal
effects arising at the electrodes of the tungsten are
lamp. Important work was by done by F. M.
Penning in regard to electrical oscillations
in a D.C. discharge in mercury vapour of low pres-
sure; in deviation from Langmuir's findings (1925)
it was proved that abnormal velocities of electrons
in such a discharge are due to the said oscillations.
Department for testing materials used in the Philips' Works.
The investigation of gas discharges, which had
been begun by IIolst, Oostcrhuis and Hertz
in the old laboratory, was continued in the new one
on a wider scale. Hertz had worked out methods
for accurately measuring excitation and ioniza-
tion potentials, mainly of rare gases, and estab-
lished a relationship between these quantities and
the spectrum (term diagram.). The resonance lines
of all rare gases were photographed with the
vacuum spectograph and their wavelengths
accurately determined. Furthermore, following up
the investigations of hoist and O o s t e r h u i s, the
low-tension are was investigated, when. it
For Hertz's experiments an equipotential cath-
ode was used which had been coated with barium
oxide, obtained by oxidation of barium. applied to
the cathode in the form of an azide and then
thermally decomposed. The experience gained with
these oxide-coated cathodes was of direct use for
the manufacture of radio valves. Tungsten as elec-
tron-emitting substance was very soon replaced by
materials (dull-emitters) which already give ade-
quate thermionic emission at a lower temperatue.
Oxide-coated cathodes soon came to be used also
for rectifying tubes filled with argon and. mercury and
for gas-discharge lamps (mercury lamps, neon tubes).
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to l'tur,iPs rl;cn ulc_~t, It1.~~tt:1K
The study of Lite spectra of rare gases had revealed
that the atoms of these gases, namely of argon and
neon, maN- be in an excited slate Winch cannot he
transformed into the ground state by radiation, such
a state being called it metastable state. After the
departure of hertz in 192.5, 11. B. I)urgelu, who
in collaboration with purger and Ornstein had been
studying in Utrecht the intensity rules for
multildets in spectra, which study was continued in
Eindhoven, took up the study of nu?tastable atom,.
nun-file tastable state and then to Lite. ground state.
It was also found possible by this means to raise the
voltage drop of a positive column in a mixture
of neon and argon by irradiation with neon light,
and even to quench the discharge if the voltage
applied is low enough.
The effect of Litt, ionization through metastable
atoll's is also apparent when investigating the
breakdown voltage V between plane parallel plates
as a function of the product purl (pu - pressure
Tungsten-ribbon lamp.; ucade in the laboratory to serve as light source, for various optical
methods of uaeasuring. The second lamp from the left has been ro shaped that, the light
reflected by the bulb does not pass through the (plane-parallel ground) windows and thus
does not interfere with the measurement. The third hunp from the left has two flat
wvindows placed someww=hat obliquely, this being useful for optical pyronietry.
These ato.ttu are capable of absorbing and re-emit-
ting certain spectral lines which the normal gas
allows to pass through unhindered. A ?itlt the aid
of this absorption the lifetime of metastable
atoms was investigated with respect to the in-
fluence of temperature and gas pressure.
Owing to their energy of excitation, in it gas l'tix-
ture metastable atoms of one atomic kind (say
neon) may ionize other atoms (say of argon), such
being possible under the condition that the ioni-
zation potential of Lite second gas is lower than the
potential corresponding to the metastable levels of
Lite first gas. In such gas mixtures various factors,
such as the breakdown voltage. are greatly in-
fluenced bw- small amounts of the readily ionizable
^omponent.
This was further investigated by Penning. The
fact that- Lite lowering of the 1lreakiioww?n
voltage is clue to the action of metastable atoms
was proved by denlonstrating that the breakdown
voltage of neon, lowered by the addition of argon,
rose again when Lite neon was irradiated ww-itlt
light which is absorbed by the inrstastahle atones,
as a consequence of which these atoms, while emit-
Ling resonance radiation, show a transition to a
reduced to 0 C. (I - - distance between electrodes),
thus determining Lite Paschen curve. Instead of
just one ruin 1111111)1 (optimum ratio of ionization and
excitation) this curve then shows two minima,
owing to an increase of luetastable atoms and thus
the formation of "secondary" ions accompanying
increased excitation.
'mothe'r anomaly of Lite Paschen curve occurs
at values of port - (PotOnain? Normally V increases
monotonically with decreasing pool, or, what amounts
to the same thing. p,,d decreases monotonically
with increasing In the case of hclium it is
remarkable that. puff as a function of I; shows a
nlnlinlnln and it maximum, so that in a certain
range of purl values three critical values of Lite
potential are fouled. J't. I., and V, Breakdown
only takes place if the applied voltage Va
answers to [ i - V n V. or E' --_ V.t. The sank
anomaly is found when in the case of stronger
currents the voltage is investigated as it function
of the current.
The study of the relation between the current I
and the voltage Vin discharges, as described above,
led also to interesting data being collected in regard
to Litt- stability of gas discharges, it subject which
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JULY-AUGUST 1951 1.891-1951
was further investigated later in the Laboratory for
Technical Physics at Delft University by Prof.
H. B. Dorgelo, Chr. van Geel and. C. Verhagen.
Finally there were interesting investigations into
the influence of magnetic fields upon discharges.
Apart from the fact that the discharge as such forms
a "current conductor" which in the magnetic field
is subject to a force perpendicular to the current and
to the magnetic lines of force, there is the influence
of the magnetic field upon the paths of the individual
electrons. The latter is particularly manifested at
low pressures, where the electrons have a long free
path. Following upon Penning's investigations
into this field a vacuum meter was constructed
in which the current in a gas placed in a magnetic
field serves as a measure for the pressure. With this
meter direct readings can be taken of pressures be-
tween 10-5 and 10-3 mm Hg and, for example, the
improvement of the vacuum in pumping installa-
tions (such as in the case of the electron micro-
scope and the cyclotron) can be followed from one
minute to the next.
We must now consider the development of
gas-discharge lamps. In 1923, following Claude's
example (1910), the manufacture of neon tubes for
advertising purposes was begun. These tubes had
(cold) iron electrodes. Instead of neon, which gives
a typical red light, other rare gases, such as helium,
were used and also mixtures of a rare gas and mer-
cury vapour. The colours could be given more
variation by using coloured glass for the tubes. Later
on, also fluorescent glass was used and fluorescent
powders were applied to the inside of the tubes so
as to produce new colour effects. With the intro-
duction of the oxide-coated cathode, already ap-
plied for rectifying valves, it was possible to make
neon tubes for stronger currents and a lower
voltage, which came to be used as beacon lights for
airfields and as light sources for special purposes
(irradiation of plants).
Scientific research kept pace with this develop-
ment. As is known, in the case of a discharge in an
elongated tube Faraday had already distinguished
a cathodic part (glow discharge) and an anodic part
(positive column), the two being separated by
,,Faraday's dark space". It is the positive column
that produces the light in neon tubes, the glow
discharge at the cathode being of no importance
in this respect. The positive column was
thoroughly investigated, theoretically as well as
empirically, by M. J. Druyvesteyn, after Schottky
had yielded an important contribution to the theory
of this discharge. An important concept is that of
the electron temperature, which characterizes the
velocity distribution of the electrons in the column
and can be measured with the well-known probe
method of Langmuir. Druyvesteyn was able to
deduce that in the absence of cumulative processes
the electron temperature is, to a first approximation,
proportional to the ionization potential of the gas.
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,prong the discharge Iambs with a filling of rare
gas and metallic vapour the .odium lamps Occupy
it special place. It is well worth -while ondining [lit,
developnnent of Lite odium l a tut p in Lite Philips`
laboratory. Discharges in sodiunn vapour had already
been investigated and used. In 1919, for instance.
such it discharge Was described bN R. .I. Strait
(l,ord Raylei-gh's son). In 1923 _1. 11. Compton and
1'(ua Voorhis (Westinghouse) investigated a large
number of gases and vapours for their ability
of producing light and thereby found also the high
light-yielding capacity of sodium vapour. They
even patented it sperial kind of glass resistant to
sodium, but. this did not lead to any useful lamp
loving developed.
In 1925 C. Hertz dcnuutstrati-d in Lite laboratory
it low-tension arc in sodiunn vapour in a bulb o1'
about 7 stn diameter. The bulb was fitted with an
oxide-coated cathode and an anode. and tails sodium
was introduced into the bulb b% electrolysis through
the glass wall, with the cathode acting as negative
pole and it bath of molten Na\(l.t as positive pole
(Warburg's method, 1890). This lamp was placed
in it furnace with a temperature of about 250 C
in order to maintain it sufficiently high vapour
pressure of the sodiutu.
Attetttiunt was again drawn to sodium as it source
of light when C. Lecher set out Lo improve. in
Lite Philips' laboratory. the yield and the colour
of the light of neon tubes by introducing a small
amount of lithium into the tube. `I'bis was an ob-
vious n>_ean-, since front the works of Kirchhoff and
Buttsen it had become known that. lithium gives a
flame a bright red colour. however, something
sluice unexpected happened: the lithium attacked
the wall of tine tube and thereby released sodium. so
that it sodium lamp was formed unintentionally.
This lamp and a number of similar tubes, in which
sodium was purposely added to it rare gas. have been
used as polariucter lanilts in tin- laboratory for
a number of years.
Meanwhile investigations conducted by I'irani
in the ()srant works had shown that under
favourable conditions more than 95?, of the energy
absorbed by the column could be converted into
sodium. light,, and talus Osrani works also brought it
polariuncter lamp on the market.
At that time the investigations carried out in.
Philips' laboratory had turned in another direction.
The use of the mercury lamp as a source of light for
medical ray treatment had led to a closer study
being made of the connection between vitamin D
and rachit is. It appeared that viteunin D could be
produced by irradiating ergoster.ine with light of a
wavelerngtlt between 2800 and 2900 A, which could
he produced by a mercury lamp or a magnesium
spark. This cotntplexity of phenomena Was investi-
gated by I'.. If. lie(-rink and A. van Wijk. The
demand arose for it special source of light for the
production of vitamin D and for anti-rachitic ray
treatment. Magnesium proved to be the most
suitahb' element for this. This led to the construc-
tion Of' it low-tension are lamp with a mixture of
rare gas and magnesium vapour; the magnesium
1n fit([ sodium latup (for direct current) and a lamp for con-
nertion (via a choke) to 220 V' alternating current. each with
its varnunt envelope. 'flit- D.C. lamps, in group; of 30 to to
ranuerted in series and fed from it rectifier, were used for the
first installations for road lighting with sodimn lamps (1932).
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was contained in the anode and evaporated into
the discharge.
This opened the way to the construction of other
metallic-vapour lamps by the same means. In con-
nection therewith, for instance, sodium was investi-
gated anew and this led to the production of a low-
tension are lamp fed with direct current and filled
with a mixture of neon and sodium vapour, which has
a favourable luminous efficiency (50-60 lumens per
watt) (De Groot and E. G. Dorgelo). In order to
give the sodium sufficient vapour pressure the bulb
was thermally insulated by placing it inside another,
evacuated, bulb. Experimental lighting systems
installed in a corridor in the laboratory and later
on in one of the roadways on the factory site soon
demonstrated the excellent qualities of sodium light
for road-lighting purposes. After the construction
of the lamp had been improved and it had been
given the form of a single bulb contained in a
Dewar flask, these experiments were continued on a
more extensive scale, inter alia in cooperation with
Prof. Dr. H. C. J. H. Gelissen, on stretches of road
forming part of the Dutch network of highways
(1932). Meanwhile Druyvesteyn and W. Uyter-
h o e v e n had been further investigating the posi-
tive column in mixtures of sodium and rare gas,
whereby it was found that this discharge, in a tube
placed in a Dewar flask, is less susceptible to changes
in the ambient temperature than the low-tension arc
lamp. It is to the merit of Bol, who had also given
the low-tension are lamp a shape suitable for manu-
facture, that the A.C. column lamp with vacuum
envelope was developed into a practical unit which
for the greater part can be manufactured mechani-
cally, also as far as the glass envelope is concerned.
The discharge tube proper has the shape of an elon-
gated U. By 1940 more than 100,000 of these lamps
had been installed. Abroad too, where similar lamps
had likewise been developed, numerous lighting
projects were carried out with sodium lamps, some
of which by Philips.
Lighting with mercury lamps has also to be
discussed. Compared with sodium lighting, at first
Philips took little interest in mercury lighting. Since
the investigations of Kiich and Retschinsky (1907),
which resulted in the appearance of the quartz-
mercury lamp with mercury-pool electrodes (arti-
ficial sun), it had been found that with mercury
vapour under high pressure (1-3 atm) a source of
light of high efficiency could be obtained. The spec-
tral composition of this light shows a striking lack
of red and as a consequence colour rendering is
inadequate. But with sodium there is still less
colour rendering and when this drawback came to be
generally accepted for the sake of the other, favour-
able, qualities of sodium light (efficiency, visual
acuity, contrast) there was every inducement to try
out also the mercury lamps. Great Britain set the
example by installing experimental lighting with
high-pressure mercury lamps, with oxide-coated
cathodes, on some highways. Eindhoven, too,
very soon started producing these lamps. But
meanwhile further developments were taking place.
The experimental and theoretical investigations
carried out by W. E l c n b a a s very soon made it
possible to survey the whole field of mercury dis-
charges as functions of the various parameters
(dimensions of the tube, mercury pressure, current
and voltage). For instance, a principle of similarity
could be worked out, whereby the number of essen-
tial parameters could be reduced and it could easily
be predicted what the behaviour would be of a
lamp with certain dimensions and containing a
certain amount of mercury.
It was again Bo1 who succeeded in drawing prac-
tical conclusions from this study and arrived at a
very compact construction of mercury
lamps, which, however, only became possible
after H. J. L e m m e n s had worked out a method
of fusing tungsten leads to quartz, using only
one intermediate glass. These lamps, only a few
centimetres in length and with an internal diameter
of 2 mm, were so designed that part of the mercury
remained in the liquid state. Owing to the con-
siderable heating of the wall of the tube these
lamps were cooled with water. The internal pressure
amounted to 100 atm and more. These lamps are
being used for cinema projectors, in television
studios and in searchlights, in general wherever
there is no serious objection against the installation
of a water-cooling system.
Another type, with a determined quantity of
mercury which entirely evaporated during the
operation of the lamp, had no need of any forced
cooling. The equilibrium pressure was 5 to 10 atm.
This type of lamp found extensive use for road light-
ing. In order to limit the preheating time the lamp
proper, which has an internal diameter of 10 mm
and a length of 35 mm, was placed in a normal
incandescent lamp bulb filled with an inert gas to
prevent oxidation of the leads. Notwithstanding
the fact that at this high pressure the mercury
spectrum shows, in addition to the much widened
mercury lines, a continuous background extending
into the red, colour rendering is inadequate, just
as is the case with the lamp with a pressure of
1 atm. This drawback can be remedied by admixing
incandescent light, but then the efficiency of the
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whole is reduced. Later it was found possible to
improve Lite colour rendering by coating the inside
of Lite outer bulb with substances which fluoresce
under the influence of the ultra-violet rays of the
mercury light.
Even when corrected with incandescent light or
by means of it (red) fluorescing substance, however,
for various reasons these lamps are not suitable for
indoor lighting. In this direction gas-discharge lamps
appeared in a different form. Starting from the low-
-pressure mercury discharge, whereby the emission
of the visible mercury lines is only small and
mainly the ultra-violet resonance lines of 2537 A
and 1849 n are produced. these ultra-violet rays
were converted into visible light by means of
fluorescence. Philips contributed much towards
tile. development of these `-TL ' to lies. By coating
the inner wall of the discharge tube with it
suitable mixture of fluorescent substances (MgWO_t,
interest in the more or less forgotten work of
A. Korrig (1891) on the subject of seeing at low
brightnesses and lie strougly advocated Lite ideas of
Schrodinger (1920) in regard to Lite use of the colour
spare for colorimetric problems. his division of the
visible spectrum into eight sections as a means
of judging colour rendering has conic to be of
almost universal use, at least in Europe. For
the practical application of Lite eight-section
analysis a special photometer was constructed by
P. W. van Alphcn.
II. Elcctrotechnics, radio and acoustics
From the manufacture of incandescent lamps
a number of important. clectrotecliiiical products
have emerged which are related to Lite property
of the filament to emit electrons, an effect which,
as already remarked, was discovered in principle
by Edison and subsequently investigated quanti-
(Zii,Mn)ZSiO,i, Cd_B2OS-1In. (Zn,Be,'.47n).oSiO.i. and tatively by Richardson,
later also other substances,
such as halophosphates) it was
possible to produce a white light
with it spectral energy distri-
bution sufficiently approxi-
mating that of daylight or of
incandescent light.
Such lamps as these. with a
gross output of 40 to 50 bu W.
are being used more and more
for all forms of utility lighting,
such as in the home, work-
shops, offices, shops. etc.. and
for road lighting.
J. Voogd and others have
been occupying themselves
with Lite photomctrv of gas-
discharge lamps.
The development of gas-
discharge lamps with their
spectral energy distribution
differing so greatly from in-
candescent light, their extensive
applications for road lighting
and the problems of colour
rendering all called for a pro-
found study of Lite properties
of the human eve and Lite
faculty of geeing under different
levels of brightness. In the
Philips' laboratory these prob-
lems were energetically tackled
by P. J. B o u m a and A. %.
KruitIt of. Bounia revived
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 CPYRGHT
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As a result of this investigation there appeared,
as we have seen, first rectifying valves and radio
valves with tungsten filament in vacuo, whilst
Philips followed the G.E.C. in producing gas-filled
rectifying valves with coiled tungsten filament.
An important improvement was the replacement
of the helicoidal tungsten filament in these valves
by an oxide-coated cathode (J. Bruynes).
With the introduction of the oxide-coated cathode
many more uses were found for rectifying valves,
because on the one hand larger emission currents
were obtained, thereby extending the field of appli-
cation to heavy currents, whilst on the other hand
the lifetime of these tubes was so extended as to
be dependent only upon the chance of accidental
damage (breakage or breakdowns) and not upon
exhaustion of the thermionic properties of the
filament (J. G. W. Mulder).
The field of rectifiers is an interesting example of
a case, often seen, where a phenomenon first found
as a small effect, so small that its existence might
be doubted, ultimately finds application on a
scale precluding any doubt as to its reality. The
currents studied by Richardson could at first only
be measured with a sensitive galvanometer. Now
a rectifying valve with an emission current of 100 A
is nothing rare.
Rectifying valves are now being made for high
as well as low voltages. Valves for low voltages
(some tens of volts) are used, for instance, for charg-
ing batteries and feeding cinema are lamps (D. M.
Duinker). In X-ray practice, on the other hand,
rectifying valves are employed which can withstand
voltages exceeding 100 kV, thanks to their being
given a suitable shape. Another important product
was the welding rectifier, characterized by a very
heavy current (H. A. W. Klinkhamer).
Within the scope of rectifier research mention
is to be made also of the work done in developing
blocking-layer rectifiers, and in connection there-
with the investigations with selenium (W. Ch.
van Geel, N. W. H. Addink).
With the advent of the triode as receiving and
transmitting valve round about 1914, radio entered
upon a new era, a development to which Philips
laboratory contributed in no small degree.
It is remarkable how often in the field of radio
practice has been far in advance of the theory.
The triode proved to answer its purpose well and
was already being applied on a large scale ever
before the relative problems, such as the calcula-
tion of the field between the electrodes and the
behaviour of the electrons in that field, had been
really mastered; the propagation of the radio waves
over long distances had been found practicable
long before scientists had got to the bottom of the
actual reason for it and before the electromagnetic
equations governing the propagation along the
earth's surface had been satisfactorily solved. In
the long run, however, it is essential to gain the
fullest possible insight into the theory of the
phenomena, and for that reason Philips have
always devoted much attention to their theoretical
investigation. Many other problems remained to be
A corner of the glass-blowing shop of the Physical Research
Laboratory.
solved in connection with the practical application
of radio valves, and so in the new laboratory radio
investigations were divided among a number of
groups of research workers. B. van der Pol was
charged mainly with the conducting of theoretical
radio investigations, whilst the more practical
investigations were carried out by E. Oosterhuis,
P. R. Dijksterhuis, Y. B. F. J. Groeneveld,
H. Rinia, B. D. H. Tellegen and many others.
Van der Pot had begun in 1922 with the study
of the triode. It had been found that the flow of
electrons to the grid and the anode, respectively
ig and ia, is a function of the voltages Va and Vg
respectively at the anode and at the grid with res-
pect to the cathode. A three-dimensional plaster
model was constructed with which this relation-
ship could be visualized. Then attention was paid
to the paths followed by the electrons under the
influence of the field and to the secondary emission
caused by the electrons impinging on the anode,
the effect of which can be demonstrated with the
plaster model. Further problems were the distri-
bution of the electron stream between grid and
anode and the effect that space charge has upon
the field; for the study of these problems a found-
ation had been laid by the theoretical investigations
of Langmuir and Epstein.
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16 PHILIPS TECTINICAI. REVII:XV
The problem of the motion of the electrons, which
has always demanded attention in connection with
the construction of radio valves, was subsequently
investigated by 1'. U. J. A. KIeynen and
J. L. 11. .1 011k e r with the aid of it model employing
small steel balls made to roll over it sheet
of rubber. This device has proved to be of great
value in eases where the mathematical approach
to the problem is too complex. Another means of
circumventing mathematical difficulties was the
tneasurintr of fields of complex electrode systems
with Lite aid of the electrolytic tank.
In connection with the phenomena arising in
the radio valve mention is also to be made of the
extensive investigation of fluctuation phenu-tt-
ena (noise) carried out In- C. J. Bakker and
M. Ziegler, which later ou was extended to higher
frequencies by It. .1. 0. Strutt, A. van der Ziel
and others.
Further, there was the investigation made I)-
Ii. 13ruining into the secondary electron
emission of solids, not only in connection with
the occurrence of this emission in ordinary radio
valves but also with it view to the construction of
special valves iiiwhiclt secondary emission is brought
about I-urposely in order to produce special ('fleets.
Following upon the study of the radio valve as
such, its behaviour was investigated when employed
as an amplifier or as are oscillator in it network com-
prising capacitances, resistances. self-inductances
and mutual inductances.
An electric network is it .system which as a rule
is governed by it number of liucar differential e(lua-
Lions. \TVltll the introduction of radio valves in the
network not only are negative resistances intro-
duced, which make it possible for oscillations to
be generated, but also non-linear terms titer enter
into the equations and make the problem more
contplica red.
Van der Pol succeeded in working out it non-
linear diffcrertt.ial equation in a simple form (the
an tier Pol equation) which incorporates all
essential data involved in the case of oscillations
and the liutiting of oscillations in networks. 'l'ltis
equation,
t?-F(t--t'") F e-.-: 0,
contains a- parameter the factor r. which to a
considerable degree determines the behaviour of rite
solution. It. appeared that within a certain range
of values (r 1) the oscillation bears a character
differing greatly from the known behaviour. Van
der Pol named these relaxation oscillations.
As opposed to 'ordinary" oscillations as may occur
when the system comprises mainly C's and L's,
and which have a sharply defined cycle, while the
amplitude depends upon various secondary con-
ditions. relaxation oscillations may arise in systems
which are governed mainly by C's and R's. In the
latter case the amplitude of the oscillations is deter-
-uined by the sy,-stent, while their frequency is highly
sensitive to external disturbances. Thus a system
showing relaxation oscillations, such as it glow lamp
shu-rtcd by it capacitor charged by it voltage source
via a resistor, can easily be synchronized with a
periodical signal, it principle widely used nowadays
in television.
Small steel balk made to roll over a shcet of rubber give
it picture of the paths followed by electrons in, for instance,
electronic valves.
NX itlt the aid of' relaxation oscillations it is also
easy to demultildy frequencies (frequency dividing)
and to produce the sub-harmonics, in contrast to
the formation of higher harmonics, which can be
obtained by connecting non-linear impedances to
it normal oscillators- circuit.
A, Van der Pol pointed out, the concept of
relaxation oscillation is also of biological importance,
where the role of' "resistance" is performed by some
diffusion phenomenon governing the biological
process. Examples are the reaction of plant foliage
to the alternation of day and night and the func-
tioning of the human heart.
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JULY-AUGUST 1951
Van der Pol and J. van der Mark succeeded
in constructing an electrical model of the heart,
built up from a number of glow discharge lamps,
capacitors and resistors, with which not only the
functioning of the normal heart but also certain
pathological aberrations could be imitated. To
our minds the medical world was too sceptical
about the value of that model at the time. Fortun-
ately, however, medical scientists of the present day
are showing more and more interest in the results
of clectro-physical and elcctrotcchnical work, as
for instance in neurophysiology. There are many
indications that in the near future closer cooperation
between the medical practitioner, the physicist
and the electrical engineer, with mutual appreciation
for the experiences and views of each, will prove
to be of great advantage to all concerned, including
the patients.
An important part of radio research is that con-
cerning the propagation of electric waves and the
interaction between these waves and matter.
First of all mention is to be made of the investiga-
tions relating to skin effect and to the penetra-
tion of electromagnetic alternating fields in conduc-
tors. The practical side of this subject was made
manifest in the manufacture of radio valves, where-
by the valve was placed in a high-frequency mag-
netic field for degassing various parts mounted in it.
It was of importance to be able to predict the degree
of heating of the parts (plate, cylinder, grid) as
a function of the field strength and of the orienta-
tion in the field; this problem was thoroughly in-
vestigated in the laboratory by M. J. O. Strutt
and others. Of particular interest are the phenomena
taking place in bodies of a magnetic material,
for there it may happen that above the Curie point
(,u ,uo) the product y (,u = ,ue,ur = permeability,
6 = depth of penetration) is small with respect
to the dimensions and below the Curie point
(,u ' ,uo) large. As demonstrated experimentally
by J. L. Snock, this has remarkable consequences
when small objects of magnetic material are sub-
jected to high-frequency heating. Upon the field
strength being reduced the temperature remains
high, owing to sufficient power being absorbed
even when the field is weak. When, however, the
temperature drops below the Curie point the ab-
sorption of power rapidly decreases and the field
has to be made much stronger to heat the body to
a high temperature again.
The radiation from aerials was investigated
both empirically and theoretically. As far as the
experimental work is concerned, extensive measure-
ments were taken, fnr inatnnnn, ~F Fh. Feld ctro gthe
in areas covered by various broadcasting stations
all over the Netherlands (R. Veldhuyzen).
Theoretically the problem of wave propagation
for a free radiating dipole had already been solved
by H. Hertz. When the dipole is placed over an in-
finite, perfectly conducting, "flat earth" the field
of the dipole and that of its reflected image can
simply be added together. Considering, however,
that the conductivity of the earth is finite and that
it has a finite relative dielectric constant, the
problem is much more complicated. For this case
Sommerfeld arrived at an exact formula as far back
as 1909, but this formula is not suitable for calcula-
tions. Therefore at the same time an approximative
formula was given for calculating the field strength
at the earth's surface. In 1919 the same problem
was tackled once more, but in a different way, by
Weyl, and in 1926 Sommerfeld showed that Weyl's
result agreed with his own. But he then put his
approximative formula in a somewhat different
form. Much has been written on the question which
of the two formulae, that of 1909 or that of 1926,
was the "correct" one and what was to be decided
by experiment. Important contributions on this
subject were given by Van der Pol and his co-
worker K. F. N i e s s e n (one of Sommerfeld's
pupils), who arrived at a strict solution in a new
form, and further by the Americans Norton and
Burrows; the exact experimental determinations
carried out by the latter proved to be in agreement
with the formulae given by Weyl and by Van d e r
Pol and Niessen.
Another question of practical importance is
what part of the energy radiated by a dipole is dissi-
pated in the earth, since from that the efficiency
of a transmitter can be calculated. This mathematic-
ally complicated problem was solved by Niessen
(1940) by employing Sommerfeld's exact formula.
The problem of the propagation of the
waves over a spherical surface has been the
subject of an intensive investigation by Van der
P o l and II. B r c m m e r following upon Watson's
work. Since in the formulae the dimensions of the
spherical surface and the wavelength are not bound
to certain values, these apply also in other realms
of physics, such as for the interaction between light
waves and droplets of water (the rainbow). A
remarkable theoretical result, for instance, is that
the radiation of the rainbow shows polarisation.
This can now easily be verified with the aid of
"Polaroid" spectacles; it seems that meteorologists
had never noticed it.
In the investigations referred to, the atmosphere
ogeneous medium. Later,
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 CPYRGHT
Onnrnvpd For Pplpacp 1999/(19174 ? C:IA P lPR3-M473RM7Ml13M13-1
I'IIILLI's 't'I?:CIINICAL, Itt:Z IEw VOL. 13, No. 1-2
Tire miller contributed important information on
propagation in an inhonlogencous atmosphere
(tit(- ionosphere, '`ducts"). In Great Britain tit(
investigation of the ionosphere had been taken
up experimentally oil a wide basis by Appleton,
who gave it lecture on this at Eindhoven in 1.930.
The root of the problem. for which no solution had
then been found, lay in the relation between the
virtual height (velocity of light in vacua X half the
reflection time) as it function of the frequency and
the concentration of free electrons as it function
of the height above the earth. From the discussions
held at, Eindhoven it appeared that, when ignoring
the magnetic field, this relationship is given by an
integral equation of Abel, so that. time result. can be
written explicitly.
At certain frequencies the reflection ti.nte is in-
finite. Van der Pot saw in this it connection with
the mysterious "delayed ecluts" which at, that time
were puzzling man radio amateurs. It is to he
noted, however, that Stiirnter had quite it different
explanation for this phenomenon and attributed
it to charged particles coating front the sun
at a great. distance from the earth (10? km and
more).
A remarkable effect of the ionosphere, discovered
at Eindhoven, is the interaction of radio
waves of different frequencies. In tile ellipty
space, owing to the linearit.v of the 11a-tuell
equations, the principle of superposition applies
exactly, so that two wave svsLeuls may penetrate
each other without airy mutual interference. In
the ionosphere, however, the interaction is partly
of a non-linear nature, witlc the result that waves
propagated through the ionosphere over it powerful
transmitter become modulated with the frequencies
of that. transmitter. "1'ellegen observed this at
Eindhoven in the case of signals from the Bero-
Iniinster station, which were subject to interference
from the powerful Luxemburg station,
the capacitance between the control grid and the
anode, which was found desirable on account of the
ever higher frequencies at which transmitting
station., were w-orking.
-With the tetrode thus formed much trouble was
experienced from the secondary emission of the
anode. Tellegen therefore introduced between
screen grid and anode a third grid (suppressor grid)
to hold back the secondary electrons. Thus arose
the five-electrode valve or pentode, which at first
was used as output valve and subsequently came
to be applied also in other circuits. On first sight
this may not seem to be it very drastic change,
but it, has proved to he an exceptionally important
improvement, since now, with a very few exceptions,
all radio valves are pentodes.
Much work has been done in investigating the
behaviour of these and other types of valves in
various funct.ions, such as for high-frequency and
audio-frequency amplification (A. J. Heins van
der Ven, J.
and others).
van Slo.otcn, 11. van Suchteten,
Considerable attention has also been paid to the
construction of transmitting valves, partly in
connection with Lite eniplo}-meat of short waves
(1.i-50 nl) for long-distance radiotelephony. An
experimental transmitter was built (J. J.
N u In a ns), provisionally equipped with a "dummy
aerial'', in which the energy normally radiated
could be dissipated. A milestone was reached in
the history of the laboratory in March 1927, when
this transmitter was connected to an aerial and
commimicatimn was established with what at that
time was the -Netherlands East Indies. This soon
gained world fame, especially when, on 1st June
19'2.7, if. M. Queers 11"ilhelntina used the transmitter
(station PCJJ) to broadcast an address to the
overseas territories.
In connection with Lite ever higher frequencies
that were being used, there was also the development
of the magnetron as transmitting tube. Philips
Research Laboratory contributed much towards a
proper understanding of Lite working of this tube.
The treatises by K. Post ]t a nt u s on the functioning
of Lite magnetron with split anode still form the
basis for all theoretical expositions in this field.
Experiment-, in range finding by means of radio
waves of 1 in and smaller generated by a magnetron
transmitter were carried out in the laboratory
before 1940 ; in the period 1940-'45 this principle
was applied on it large scale elsewhere in the form
of "radar".
The designing and manufacture of radio valves
calls for great care and special methods. As higher
In addition to this, for the greater part, purely-
scientific research it considerable amount of work
was directed towards the practical side of radio,
in connection with bout radio valves and further
radio equipment. Above all, as was only natural,
radio valves underwent repeated changes. There
was a universal rational dimensioning of the various
electrodes. In itlany cases the filament was replaced
by an indirectly heated cathode. A second grid
was introduced, first as .pace-charge grid and later
as screen grid (hull). so as to render the io-19
characteristic less sensitive to anode voltage fluctu-
ations and, furthermore, with tike object of reducing
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II.M. Queen Wilhelmina, accompanied by IT. R. II. Princess
Juliana, addressed Her subjects in overseas territories via
the Philips' transmitting station PCJJ on 1st June 1927.
frequencies came to be used the connections had
to be shorter and so different methods had to be
found for constructing the electrode lead-ins.
The solution was found by applying pressed glass
or sintered glass (Lemmens) and special metals
for the leads. This development came for a large
part from the factory laboratories.
At first radio valves and some radio parts, such
as high-tension units, audio-frequency transformers
and resistance-capacitance couplings, used by
amateurs and set makers, were the only radio
products manufactured in the works. However,
with the increasing popularity of radio broad-
casting there was such a big demand for radio
receivers that it became worth while to start manu-
facturing complete receiving sets. Looking back
now, it is hardly imaginable that 25 years ago this
was regarded as being something out of the ordi-
nary.
Almost at once the need was felt for an apparatus
that could be worked without batteries by feeding
it entirely from the mains. This was made
possible by employing the indirectly heated
cathode which had meanwhile been developed at
Eindhoven.
In the construction of radio sets, as already re-
marked, a great many problems were involved
which had to be solved in the laboratory, in the
beginning even in all sorts of constructional details
(Bol, C. J. van Loon, J. M. Unk). On the one hand
there was a need of certain circuits which had to
be as efficient as possible while at the same time
being easy to make and to repair, and on the other
hand accurate methods of measuring were needed
for testing the functioning of experimental circuits.
Much attention was devoted to the coils. By
making these as loss-free as possible (according to a
principle evolved in this laboratory by H. R i n i a)
greater selectivity was obtained and a "straight set"
could be built with four tuned circuits, which for
a long time answered the purpose very well. As
the "ether" became more and more crowded with
the increasing number of stations working within
the allotted frequency bands, so that short
waves came to be used for broadcasting, receivers
had to be built on the superheterodyne principle.
Of great importance was the invention, by
Metal leads and supporting rods can be fused into bases of sintered glass in an almost un-
limited number and in any order.
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PIIIL,IPS "I~ 1:CII ~[C.1I, RE II?1~i VOL. 13, 'No. 1-2
Posthumus, of negative feedback, for which
patents were obtained already in 1928. This prin-
ciple, which reduced distortion due to curvature
of Lite valve characteristic,, was very soon intro-
duced in Lite Philip, receivers. It proved, however.
to have a much wider scope than this, so that at
the present day it is being employed in practically
all amplifiers and in all kinds of regulating devices,
etc.
For those cases where it highly constantvoltage
(low internal resistance) is required for feeding
radio apparatus a self-regulating high-tension supply
unit was developed (Ilinia, 11. J. Lin denhovi us).
In connection with snkootiling systems for the
feeding of radio apparatus retention is to he made
of Lite considerable amount of work clone in the
field of electrolytic capacitors (Van Cccl,
A. Claassen).
A difficulty encountered in Lite manufacture
of radio sets lay in the lack of uniformity of electric-
al networks, especially since there are bout direct
and alternating current mains. J. W. Alexander
constructed vibrator-converters capable of
converting direct voltages of 100 to 200 V into an
alternating voltage. Such vibrators are note conn-
monly used with car radio sets for converting Lite
battery voltage of tt or 12 \ into an alternating
voltage of 220 V.
Another problem lies in the feeding of receivers
in places where no stains are available. In the place
of accumulators and dry-cell batteries the tliernio-
electric generation of current was thought of,
but this is too uneconomical. This suhscqucnth-
led to the development of the air engine, which
,
o
rect an
y
p
before long will be able to take Lite place of the means of gramophone records or a Mill
t
er
ape.
petrol engine now. used for this purpose. Important. work has also been done in the field
of the physiology of hearing. Particular mention
In the development of radiotelephony there is is to be made of J. F. Scltouten's investigations
also the problem of conversion of the radio signal into the validity of the so-called Ohm's acoustic
into audible vibrations of the air, thus into speech law, from which it. appeared that in a mixture of
or music. As it consequence acoustics, and especially frequencies which are it multiple of a certain funda-
elcctro-acoustics, have become inseparably connec- mental frequency the latter can sometimes be heard
Led with radio. In 1925, when under the guidance even if it is not itself present in Lite mixture (the
of H. ernneulen Philips started making loud- ..residue" t.heory).
speakers, these were built on Litt- electromagnetic Further, L. Blok designed various signal gener-
principle, whereby the movement of an armature ators, which have been applied, inter alia, for
is transmitted to a diaphragm. Then there appeared audionnetric investigations.
the moving-coil loudspeaker, in which the cone- Other developments in the technique of sound
shaped diaphragm is connected to it small cylin- reproduction will be dealt wit-11 in the last section
drical coil through which the varying signal current. of this review.
flows and which is placed in a radial magnetic
field. This magnetic field was at first produced by The development of television began already
means of a soft-iron circuit excited with direct in the thirties. In its earliest stages a Nipkow
current. Philips very soon replaced this circuit disc with =18 lines was used both at the transmitting
by it permanent magnet. This development
involved intensive research in connection with
magnet steel, it subject which will be referred to
again elsewhere. The new magnetic materials also
made it necessary to give the magnets a different
shape, so that attention had to be paid to the de-
signing of magnetic circuits (A. Ti!. van Urk).
In addition to Lite work involved in the develop-
ment of loudspeakers, much work has also been
put into the development of power amplifiers,
which in turn led to great activity in the field of
line telephony (W. Six, If. G. Beljers, J. to
Winkel).
In connection therewith attention may be drawn
to Lit(, various measuring instruments develop-
ed in the laboratory, such as a measuring bridge for
measuring losses in coils and capacitors, with which
phase angles can be measured with an accuracy
of 10 `' in it frequency range of 103 - 105 c/s (J. W.
K61iler, C. C. Koops).
Further research work led to the development of
various types of microphones, gramophone pick-ups
and gramophone motors, and finally sound reproduc-
tion for the sound film and for broadcasting studios.
An important part has been played in this by the
Philips-~1liller process, whereby it width-nnodu-
lated track is cut. in it celluloid tape coated with a
lacquer, after which it is scanned by the known
optical means. An advantage of this system was
that the recording could he played back at once and
thus corrected where necessary.
In this connection mention is to be made of a
system, developed by K. do Boer, for stereo-
phonic sound re
roduction
b
th di
dl
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JULY-AUGUST 1951 1891-1951
and at the receiving end. Subsequently a cathode-
ray tube was used in the receiver, whilst the Nipkow
disc, still employed for the transmission, was per-
fected for televising films (Rinia). Later on the
Zworykin iconoscope, meanwhile developed in the
U.S.A., came to be used for TV transmission, first
for the 180-line system and later for larger numbers
of lines (Van der Mark, G. Hepp, A. Venis).
Experience was gathered in the construction of
amplifiers (J. Haantjes and others) and the build-
ing of transmitters (W. Albricht). Experiments
In 1937 already a transportable installation for television
transmission and reception was completed and taken on tour
for demonstrations over a large part of Europe. It could be
worked on the system of 405 lines or on that of 567 lines.
were also carried out
by means of lenses,
tube with
with projection television
employing a cathode-ray
screen (M. Wolf). Complete
mobile television apparatus
in two motor-vans, with
was built and installed
which demonstrations
in Western Europe
Copenhagen, Stock-
Europe (Budapest,
Warsaw). Owing to
were given in various places
(Utrecht, Brussels, Antwerp,
holm) and also in Eastern
Bucarest, Zagreb, Belgrade,
the outbreak of the war these
abrupt end in 1939.
to an
III. Chemistry
It would be saying too much to maintain that all
the chemical problems tackled in the Philips labora-
tory in the course of time likewise emanated from
the incandescent lamp, but for a very large part
such is indeed the case, either directly or indirectly.
Disregarding the metallurgy of the tungsten and
the making of the glass, in the manufacture of the
incandescent lamp chemical problems arise from
the action of the gases released from the wall of
the bulb and the metal leads upon the glowing
tungsten filament, whereby traces of water vapour
have a particularly disastrous effect. In the
dissociation of the water vapour by the filament
oxygen is combined with the tungsten and forms a
volatile tungsten oxide which is precipitated on
the glass wall of the bulb. The remaining hy-
drogen in turn reduces this oxide to metallic
tungsten. Thus, owing to this "Langmuir's cycle",
tungsten is continuously being transported to the
wall of the bulb, so that gradually this is blackened.
It is therefore essential to remove water vapour
and other gases, and this is done by introducing
into the bulb a substance, such as phosphorus,
which combines with the residual gases into a
non-volatile and harmless product. Such a sub-
stance is called a "getter". In radio valves, where
phosphorus cannot be used on account of its high
vapour pressure and residual gases are moreover
obnoxious because in the ionized state they affect
the oxide-coated cathode and give rise to grid
currents, and in X-ray tubes, where residual
gases increase the risk of breakdown, metals like
barium and zirconium are used as getters.
Even though the bulb of an incandescent lamp
may not contain any gases attacking the filament,
still evaporation of the tungsten takes place. In
course of time this evaporation likewise turns the
bulb black and thus the yield of light is reduced.
Furthermore, the filament itself is reduced in thick-
ness and as a result eventually collapses. The same
applies in the case of the gas-filled lamp. The pre-
vention of the evaporation by the gas-filling as
such is offset by the filament being heated to a
temperature so much higher that the lamp has
about the same lifetime, so that the only advantage
gained is the higher efficiency.
The manner in which this evaporation of the
tungsten takes place differs according to whether the
lamp is filled with gas or evacuated. In a gas-filled
lamp the tungsten atoms come into collision with
the gas molecules time after time, so that they
have an opportunity to combine into aggregates
which move about in the gas in the form of sub-
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 CPYRGHT
microscopical flocculations and eventually settle
upon the wall of the bulb. Owing to convection
this shows a preference for that part of the latup
which in the burning position is uppermost. thus
not Lite part through wlticlt most of Lite light passes.
With the vacuum lamp the situation is different:
the tungsten atoms travel in a straight line from
the filament to the inner wall of Lite bulb. It can
be imagined that upon striking tile glass wt all Lite
tungsten atorn is repelled like it minute metal ball.
but we know that ultintatef.v it adheres to Lite glass,
so every time Lite atom strikes against [lit- wall
it must lose some of its kinetic energy.Lartgnucir's
conception was that upon collision with Like wall
Lite atom tetuporarily adheres to it and is then.
as it were, again evaporated, thus implying a certain
"adhesion time". By accurate experimentation
this has been confirmed by f:lausirtg. It is true
that in the case of cadmium atoms oniv an upper
limit (10 " see) could be found for this adhesion
time, but in the case of argon atotus on glass at
temperatures of 80 to 90 K adhesion times of
10 to 10 sec were found.
This matter of the evaporation of tungsten has
been dealt with at. sotne'lengt.h because Lite investi-
gations carried out in connection therewith formed
an introduction to further investigations into the
adsorption of tungsten atoms and tile resultant
absorption of light. So long as the tungsten atoms
remain isolated on the wall of Lhe bulb there is
no appreciable absorption of light. but the position
is different when they form a continuous laver of
metal. In order to minimize Lite absorption of
light, therefore, before the mount is fused into Like
bulb the filament is sprayed not only with the
getter but also with a little salt, say CaF.0. As
soon as the filament is heated to a high tempera-
ture this salt evaporates and is precipitated on
Lite wall of the bulb as an invisible thin layer. The
tungsten atoms conking from the filament shoot
into this laver of' salt, Like particles of which keep
the atoms separated. so that very much less light
is absorbed.
About 1920 little was known with certainty-
about the effect of such layers of salt. Investigations
into their action carried out in Philips laboratory.
mainly by J. 11. de Bocr. extended over a period
of more than 15 vears. It. has thereby been found
that the laver of salt is not to be regarded as a
homogeneous mass but as an agglotuerat:ion of
minute crystal lamellae about 10 " cut thick lying
criss-cross one on top of the other and thus forming
a very large active surface, tens of times greater
than the surface of Lite glass covered by them. The
tungsten atoms are adsorbed on the surface
of Lite crystals. 'I'll(- intensive study of Lite adsorp-
tion of atoms and molecules (e.g. caesium and iodine)
in such layers of salt (Dc Boer, C. J. Dippel,
C. F. V'c e n e ni a n s) has yielded very important
results.
Metals like caesium may be adsorbed also on
tit(- surfaces of metals. in which case they have the
property of reducing the work function of the
metal and thus increasing the electron emission,
bout the thermionic cnntission and that brought
about by irradiation with light - photo-electric
effect. By oxidizing the adsorbed laver and again
precipitating caesium onto Lire laver of oxide
it is possible to produce complex layers with an
exceptionally strong photo-electric effect (M. C.
Tc v e s). The study of this emission was of import-
ance for the construction of photocells, for which
there was a need in connection with the sound
film. '1'lo' deeper insight gained into the nature of
these lavers opened up new possibilities, such as
the entplovinent of the *'light transformer" for
converting infra-red rays into visible light (Hoist,
De Hoer. Tcyes), Lite construction of tike electron-
multiplying valve and, later. the television pick-up
tubes.
't'ile investigations into Lite vaporization of CaF2
also led to other compounds, such as ILiB03,
K..B1' , being tried out for tile. same purpose, as
a result of wlueh the volatility of various compounds
was studied.. Wlkv, it may be asked, is NaCl for
instance a substance having a high melting point
and it negligible vapour pressure at room tempera-
ture. whereas WC1G is a substance that readily
melts and is easily evaporated? From the point of
view of the theory of heteropular chemical com-
pounds Like answer is simple. The molecule of
NaCl is built up from it positive sodium ion and
a negative chlorine ion, which together form an
ch?ctric dipole, so that: two i aCl molecules exercise
a very strong attractive force upon each other.
In the case of \VCls. on Lite other hand, the central
metallic ion is surrounded by six chlorine ions
screening off' Lite charge of the central ion, so that
there is no great attraction between neighbouring
molecules. The theory of the lie terop o far chemic-
al b u nd was formulated by Kossel in 1920,following
upon Bohr's work. It is mainly due to the work
of \'an Arkel in this direction that a more or less
coherent explanaLion was established for the most
important facts in anorganic chemistry, an explana-
tion that, is of great value as a basis for chemical
thought and for education in chemistry-. It is fortu-
nate that this was more or less completed before
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 CPYRGHT
*ppiaved Fa. Release i999te9t24. el*-Rl3P89-ee429Ree2E1ee1 See! 9-1.
JULY-AUGUST 1951 1891-1951
the conception of the homeopolar bond came into
more prominence as a result of the development of
quantum mechanics. Thus the one-sided-hetero-
polar aspect could gradually be introduced into
the new system without losing its value.
In connection with these investigations the
energy of formation of a number of molecules and
crystal lattices was calculated and the relative
stability of various molecule models investigated.
known that WC16 and hydrogen on the surface of
a heated tungsten filament may react one upon
the other and form tungsten, which is deposited
on the wire. When a mono-crystalline wire is taken
(Pintsch wire) also the growing metal becomes a
mono-crystal. In the Philips laboratory it was
found that dissociation of WC16 at elevated tempera-
ture takes place also without hydrogen; attempts
were made to produce other metals in the pure
Measuring the spectral transmission of various materials in the ultra-violet range. On the
right the source of ultra-violet radiation and the m.onochromator. In the centre, in a
screening cage, the measuring apparatus with photoelectric cell.
The above conceptions were also applied to the
relation between physical properties of homo-
logous organic compounds, as for instance
the relation between the boiling points of CH4
and of the compounds obtained when replacing in
CH. one or more hydrogen atoms by atoms of
F, Cl, Br or I. Subsequently, after Van Arkel's
appointment as professor at Leyden, this investi-
gation was extended by him and his students to
a large number of other compounds. Also worthy
of mention is the study of the dielectric behaviour
of organic dipole molecules in solution, which led,
inter alia, to the "Van Arkcl and Snook formula",
which was later investigated theoretically by
Onsager and by Bdttcher.
The study of the volatility of metal compounds
had also important technical consequences. It was
state in this way. Perhaps the most striking result
was the preparation of titanium, zirconium,
hafnium and thorium from their iodides by
precipitating the latter on a thin tungsten wire as
core (De Boer and J. D. Fast). In this way
titanium and zirconium, known as being greyish
brittle substances of a doubtful metallic character,
were obtained in the form of fine lustrous metallic
products. The rods, consisting of a few large crystals,
proved to be highly ductile, so that they could be
drawn into wire and rolled into foil. This is particu-
larly of importance in the case of titanium, consider-
ing the interest taken in this metal in recent years.
Ductile zirconium has found important applications
in vacuum technics. Applied to the anode of a
transmitting valve it proves to be an excellent
getter, on account of the almost unlimited capacity
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 t^.PYRC;HT
21 PHILIPS TECHNICAL REVIEW,'
of this metal to adsorb oxygen and oilier gases.
The oxygen taken up in the metal has a negative
charge, as appears from the fact that. in an oxygen- further investigated by Van !lrkel, Snock and
charged rod of zirconium through which a direct
current is ]sassed the oxygen migrates towards
Lite positive pole.
The knowledge of metals and their interaction
with gases proved to be of great value to the labora-
tory staff when it was decided to nta nufacture
welding rods (J. Sack, P. C. van der V illigen),
in addition to the welding rectifiers and rectifying
valves already being produced.
The study of tungsten wire and the behaviour of
tungsten in processing led to extensive research
in Lite domain of reervsLallizat.ion. A substance
particularly suitable for this is aluminium, which
is easily deformed and recrystallized at. co-nparaLive-
Iv low temperatures ( 600 C), while the process
of this recrvstallization can be followed by etching
in aqua regia after removal of the superficial oxide
with caustic soda or hydroll uoric acid. This simple
technique. supplemented by crystallographic study
(W. G. Burgers, J. F. It. Custers). led to a deeper
insight into the essence of the formation of crystal
nuclei. This study is still being continued at the
present. day by Prof. If'. G..Burgers in the inorganic-
chemical laboratory of Lit(, Technical University
at Delft.
Finally, in connection with applications in Lite
field of clectroteclutics and acoustics (transformers,
loudspeakers), extensive research has been carried
out in regard to Lit(- magnetic properties of
metals, particularly of iron and iron alloys (G. J.
Sizoo, W. F. Bra-tdsina, Elc-abaas, .Jonas,
Snock, Six, G. W. llathenau. J. J. Went,
11. J. Meerkamp van Hoiden).
Special products, Lite fruit of years of'study in Lhis
domain, were the rolled nickel-iron ("Fernicube")
with strong anisotropic properties, for loading
coils, and magnet steels with exceptionally high
coercivity and high value of the (111311;,
product, which are widely used not only in loud-
speaker magnets but also in pocket and bicycle
dynamos.
Of importance for the investigations both of
magnetic and non-magnetic metals was the work
done by Snock in studying Lite magnetic after-
effects of iron, whereby it. was found that these
effects are related to the presence of traces of carbon
and nitrogen, which influence not only the magnetic
but also Lite elastic after-effects. Both these
are governed by a sort of diffusion of C and _N
atoms present in interstitial places to neighbouring
interstitial places.
Other materials studied at Lite time in the labora-
tory are Lite ferrites, which since 1934 have been
1:..1. W. Verwev.
Preparation of magnet I eel. IE;mpLy?ing the furnace in which the
alloy Inn. been melted by induced high-frcquenev currents.
This led, inter alia, to the view (De Boer and
Verwey) that it substance like Fe3O4 derives its
conductivity from Lite fact that. ions of one and
the same element but of different valency are
present in crv stallographically identical places and
thus make it possible for an electron to pass over
from one ion to another.
In tine course of the resultant investigations our
research workers became familiar with various
problems of the solid substance, in particular with
oxidic systems, of which the spinets form an inter-
esting sub-group. `1'111' latter were further studied
both in respect to their electrical properties (Ver-
wev and others) and with regard to their magnetic
properties (Snock). The study of the electrical
properties led to the development of semi-conducting
materials. while that of the magnetic properties
yielded the important magnetic material "Ferrox-
cube", which will be dealt with later.
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The previously mentioned work by De Boer
and others on the adsorption of atoms on crystals
was extended to cases where atoms are built into
a crystal lattice, a subject to which much attention
was devoted in Germany by Pohl and his pupils.
What is particularly due to De Boer is the disclo-
sure of the fact that the place of a lacking negative
ion in an ion lattice may be occupied by an elec-
tron and that, at the cost of only a little energy,
this electron may be brought into a state in which
it acts as a conduction electron.
It was at that time that the programme of
work on solids was given shape, which later on
was to occupy the minds of such a large part of
the scientific staff of the laboratory and comprised,
among others, the investigation of luminescent
substances.
The luminescent substances (lumin.ophores or
phosphors) used for converting the ultra-violet
light of gas-discharge lamps into visible light are
prepared according to methods evolved by Lenard
round about 1890. These investigations in the field
of luminescence are to be regarded as classical and
have not yet lost any of their value. They revealed
in particular the fact that the luminescence of sub-
stances like zinc sulphide is due to the presence of
extremely small admixtures of certain metals,
such as copper and silver (activators).
When it became evident that large quantities
of luminescent materials would be needed for light-
Phosphors are exposed to an electron beam in a vacuum tube and tested
for their fluorescing properties.
ing purposes Philips began to take up
the manufacture of these substances
and, at the same time, the study of
the phenomena of luminescence. This
study covered both the physical aspects
- such as the spectral composition
and the intensity of the luminescent
light as a function of that of the
incident rays, the decay of luminescence
as a function of time in the case of
discontinuous irradiation, the relation
between luminescence and temperature,
luminescence under the influence of
cathode rays and X-rays - as well as the
chemical aspects, such as the influence
of the composition and of the conditions
during preparation upon the lumines-
cence, and the influence of admixtures
(quenchers, sensitizers) upon the inten-
sity of fluorescence. Often the chemical
and the physical problems are so closely
interwoven as to be inseparable, so that
close cooperation between physicists
and chemists or the combination of
physicist and chemist in one person
is essential for these investigations.
Important physical results lay in the
deeper insight thereby obtained into the
mechanism of fluorescence and phos-
phorescence, the transfer of excitation
energy in phosphors and the relationship
between persistence and quenching as
a function of temperature (F. A.
Kroger, H. A. Klasens).
Chemical results lay in the deeper in-
sight gained into the properties of zinc
sulphide and related compounds and of
substances such as Zn2SiO4-Mn2SiO4 and
other manganese phosphors (Kroger).
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 CPYRGHT
In Lite foregoing some cases have already been
mentioned where organic compounds were studied.
Mostly these concerned simple organic molecules
which are very closely allied to the inorganic
compounds.
But work has also been done in the field of or-
ganic chemistry proper, na-nely in that of compounds
with large molecules. such as gelatin. cellulose,
proteins and synthetic resins. Gelatin was thor-
oughly studied because this substance serves as
base for Lite Philips-Miller tape (Diit pc1, A'erin eu-
len) used for sound reproduction; this tape con-
sists of a celluloid carrier with it transparent coating
of modified gelatin. covered by it non-transparent
layer of IIgS-sol in which the cutter of Lite recording
apparatus traces a "sound track".
Artificial resins were originally studied with
a view to Lite possibility of using these materials
for making Lite bases of radio valves and loudspeaker
baffles, and later for snaking various parts and the
cabinets of radio sets from these materials. The.
phenols hardened with formaldehyde, which had
been named bakelite after Lite Belgian chemist
Baekeland, were. placed on [lie market by Philips
in a large number of varieties under the trade name
"Philite".
A third group of organic compounds, the diazn
compounds, was intcosively investigated ill the
Philips laboratory when it was contemplated to
produce dye-line paper, in addition to the mercury
lamps destined for the dye-line process. With
the aid of these compound, in various carriers,
such as cellophane, paper. cellulose esters, etc.,
materials for photographic reproduction were pro-
duced which, via conversion of the products of
dissociation through light into a developable latent.
metallic image, ultimately vield silver images with
a resolving power of 1200 lines per min. which
appear to present interesting possibilities of appli-
cation (Dippel, R. J. II. Alink, K. J. Keuning).
Attention was also given to tile study of colloid-
chemical problems. One result of these invcatiga-
tions, which was of importance for the manufacture
of radio valves, was a new method of coating
cathodes with a layer of oxide, covering then by
means of electrophoresis with finely distributed
carbonates of barium and strontium, which are
afterwards turned into oxides. Also the insulating
layer around the filament of utdirectly-heated
cathodes is applied in this way (De Boer, L erwev,
II. C. IIautaker).
This concludes Lite review of chemical research in
Lite Philips laboratory prior to 19.10. A number of
investigations carried out with metals and with
non-magnetic and magnetic ceramic materials,
glass and semi-conductors will be dealt with in Lite
last section.
IV. X-rays
From the radio valve it is but one step to Lite
X-ray tube. Any diode is in principle a source of
X-rays, and it does in fact become so when Lite
electrons strike Lite anode with sufficient energy.
With Lite X-ray tube problems arise which are simi-
lar to those encountered with the radio valve, such
as Lite shaping of Lite electrodes with respect to
the nature of Lite electric field, Lite paths followed
by primary and secondary electrons, and Lite focus-
ing. To these are added the typical problems connec-
ted with high tensions, as for instance Lite efficient
distribution of potential differences. Since only a
small fraction of the electron energy is converted
into X-rays and the rest is absorbed in the anti-
cathode in the form of heat, it is a great problem
how to carry off that heat: by providing for suffi-
cient dissipation of this heat and giving Lite anti-
cathode it suitable construction it has to be ensured
that in the focus Lite material struck by Lite clec-
tro-ts does not melt.
Of physical importance is the measuring of Lite
intensity of the X-ravs and Lite strength of the dose.
Much attention has therefore been devoted to
this problem by A. B o u iv e r s, who took up X-ray
research in the Philips laboratory in 1920.
I,t the construction of X-ray tubes one is. con-
fronted with such problems as Lite safeguarding of
the users of X-ray apparatus against scattered
ravs and high tension, the raising of the specific
load. the requirement of easy handling, and Lite
applications in connection with a proper formula-
tion of the optical requirements which Lite apparatus
has to answer; these applications may be of a
medical (diagnostics and therapy), a physical
(examination of crystals with X-rays) or a tech-
nical nature (examination of materials).
An important, discovery was Lite possibility of
fusing glass to metal, for which the chrome-iron
already -nentioned was used. This made it possible
for U0uwers to build rugged X-ray tubes, which,
since the part where the rays are generated is en-
tirely enveloped in metal, afforded the maximum
of safety against undesired radiation and, moreover,
allowed of it simple safeguarding of the user against
high tension by earthing the metal shield.
Tubes came to be developed for still higher
voltages and for larger powers, both for diagnostic
purposes and particularly for therapy.
A special form of X-ray tubes which should be
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mentioned is the rotating anode
tube, which was first developed by
Bouwers in cooperation with J. H.
van der Tuuk. The problem of the
dissipation of heat in these and other
anodes was thoroughly investigated
by W. J. Oosterkamp.
Further, special tubes were designed
for crystallographic re,arch with the
aid of X-rays,ip.-;;`nich the anticathode
was mark= of special materials, such as
molybdenum, copper, iron, etc., because
these are required to yield approxi-
mately monochromatic rays of a known
wavelength.
In the beginning all X-ray tubes
were made in the laboratory, but later
a separate factory was opened. The
main features in the manufacture of
X-ray tubes are well studied and well
applied technology (getters!) and the
exercising of extreme cleanliness in
handling the materials.
Apart from the development of the
X-ray tubes themselves, that of the
apparatus for supplying the high tensions
required for the working of the tubes,
as also that of the control desks,
forms a considerable part of Philips'
activity in the field of X-rays. Often
alternating voltage has to be trans-
formed into direct voltage, for which
special rectifying valves are needed,
One of the first practical executions (1937) of a cascade generator, for 1.7 MV
direct voltage.
which formerly had a tungsten cathode but now
have either an oxide-coated cathode or one of
thoriated tungsten.
Side by side with the aim towards higher tensions
and greater powers, provision was also made for
cases where a relatively low voltage and a small
67064
One of the first experimental X-ray units of very small dimen-
sions (1933), a forerunner of the "Centralix" and "Oralix"
apparatus.
power suffice. Small X-ray apparatus was therefore
developed in which the tube and the transformer
are incorporated in one single unit. Such units
serve as portable apparatus for diagnostic work
and, for example, as X-ray apparatus in dentistry.
It has even been possible to produce a complete
X-ray apparatus so small that it can be carried
in the pocket, and yet it yields a satisfactory beam
of X-rays.
From investigating current sources for high vol-
tages B o u w e r s arrived at the principle of voltage
multiplying by means of a cascade circuit.
Subsequently it appeared that this principle had
already been recorded by Greinacher and that it
had also been applied by Cockcroft and Walton
for nuclear-physical research in the Cavendish
laboratory. As a special feature of Philips' develop-
ment in this field is to be mentioned the elegant
solution of the heating of the filaments in the valves
by high-frequency current (A. Kuntke). A number
of high tension generators of this type, for tensions
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 r pyRnuT
Small rectifier in cascade ronncction. ronsi.ting of selenium
valves and capacitors. Connected to 2211 r altcruaItug voltage
it yields 12011 V direct \nlIagr, with which, for itt taurr, a
radiation counter tube ran be fed.
up to 2 MV, have becu Intilt at Eindhoven for insti-
tutions in several countries.
Once it became. possible to generate high tensions
it was only a logical setlueuce to take up also re-
search in nuclear physics. Il o u we rs and F. A. 11 e y ii
designed an ion-accelerating tube with which the
constructed by Penning, whereby deuterium ions
the working of this apparatus, scientific nuclear
research work was carried out with it. In the course
of that work lie vu discovered the. (it, 21t) reaction
with Lite elements Cu and `Ln, by which reaction
the nucleus is struck by one neutron and yields
two neutrons, this being accompanied by the for-
ination of it radioactive isotope of the same atomic
number but lighter than the basic isotope. In 1939
A. IL W. Aten, Bakker- nd IIevn studied the
transmutation of uranium and [li ium by neutrons.
In this connection mention is also to`i;cMade of
a neutron tube without a separate ion source
are accelerated in a gas discharge and Lite target
is placed in the discharge tube itself. In order that
sufficiently high voltages can be applied and the
free path of the ions made large enough, the tube
is filled with deuterium under it very low pressure
and the discharge space is placed in a magnetic
field so as to constrain the electrons to follow long
paths. just as in till' case of the manometer described
earlier. thus making it. possible for the discharge
to he maintained under the low pressure.
Installation for X-ray therapy, working iaitli it voltage of l-00 kV, supplied
in 1911 to the Academic [lospital at Groningen.
ions of' deuLeritim, formed in a separate ion source.
could be accelerated to an cttergl of 1.2 11e\ and
focused upon a target of bervlliuni or lithium. Thus
a powerful neutron source is formed by means
of which materials placed in its vicinity can be
made radioactive. In order to gain experience in
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PHILIPS TF.CII.,\fcm. REVIEW VOL. 13. No. 1-2
V. Mathematics and theoretical physics
With the growth of the laboratory more and
inure interest was taken in theoretical-physical
and mathematical research. whereas on the one
hand. besides development work for practical
applications, experimental physical research is
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necessary to obtain a deeper insight into the prob-
lems, so on the other hand fruitful experimentation
is only possible when at the same time the necessary
attention is devoted to theoretical physics. This
implies that the necessary mathematical apparatus
has to be mastered and where possible further
developed. This applies more or less to each of
the groups already dealt with. Both the study of
gas discharges and radio research, as well as the
physico-chemical studies and the work on X-rays,
had each in turn their own mathematical problems.
In regard to gas discharges there was the mathe-
matical treatment by G. Hertz of the diffusion
of electrons in an electric field. The method followed
by Hertz has served as an example for many theo-
retical calculations in this field (D r u y v e s t e y n,
Penning, De Groot). This brought us a step nearer
to the ideal: to explain the various forms of dischar-
ges with the aid of a small number of data concern-
ing elementary processes (the probability of exci-
tation and ionization in the case of collision of
electrons and atoms, etc.), in much the same way
as the kinetic gas theory relates the measurable
quantities, such as pressure and temperature, to
the elastic collisions between gas molecules.
Further it has already been seen, for instance,
that with the aid of considerations of similarity
the phenomena in discharges in mercury vapour
of high pressure can be reduced to one single aspect.
Once he had become familiar with this method of
calculation, and following upon a publication by
Nusselt (1916), Elenbaas was able to apply similar
considerations to the phenomenon of thermal
emissivity through natural convection. The need
for this arose from the manufacture of blocking-
layer rectifiers in connection with the dimensioning
of cooling fins, but also other problems of convec-
tion can be considered in this light, such as the
heat dissipation of horizontal cylinders, which
brings us back to the gas-filled incandescent lamp
designed by Langmuir.
The part of the work programme that lent most
stimulation to the practising of mathematics was
radio. Mention has already been made of important
mathematical problems which arose in connection
with the propagation of waves. Van der Pol
took up the study of the wave equation and the
potential equation, not only in three dimensions
but also in the cases of fewer or more than three
dimensions.
As is known, the propagation of waves can be
treated in two ways, either as a whole, by the solu-
tion of a "wave equation", or by an approximativc
solution of the behaviour of a narrow beam or "ray".
The latter method is well known from the theory
of light; the image produced by a lens is not usually
studied by starting from the representation of a
wave but by investigating how the rays of light
are refracted by the lens. In the case of radio waves
Bremmer has investigated in how far results
can be reached with this geometrical-optical
approximation.
In addition to radio, particularly the theory of
atoms has formed grounds for excursions into the
field of mathematics. It is remarkable how closely
the mathematics of these problems are associated
with the mathematics encountered in the field of
radio and acoustics. In 1925 Schrodinger showed,
for instance, that the motion of an electron under
the influence of an electromagnetic field has to
be described by a wave equation which shows a
certain resemblance to the equation representing
the propagation of light or sound in an inhomoge-
neous medium, and that the classical consideration
of an electron as a "particle" describing a "path"
is to be compared to that conception as geometrical
optics compare to wave optics. The quantity used
by Schrodinger to play the part of "field strength"
or "deformation" of the medium, and which he
denotes by 11, has the property that 1I 21 is a
measure for the probability of finding a particle at a
certain place. Owing to the similarity between these
problems and those of the propagation of waves
encountered in radio and acoustics, theorists in
the respective fields soon understand each other
and find interest in the results of each other's work.
In dealing with the problems connected with
oscillations in networks or the propagation of radio
waves one mostly has to do with more or less com-
plicated differential equations. Heaviside showed
that in many cases the differential symbol, d/dt,
can be regarded as an algebraical quantity (usually
represented by D), with which ordinary arith-
metical operations can be carried out. In this way
he was able to derive deep-lying results by simple
means.
This operational or symbolic calculus was
at first received with much scepticism, but later
Carson (1926), for instance, found it to be justified.
What Carson's formula amounts to is the furnishing
of a function f(p) corresponding to a function h(x)
by the Laplaec transformation:
00
f(p) = p f cPx h(x)dx.
0
The shape of f(p) depends, of course, upon h(x).
This function f(p) is said to the be "image" or the
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"translation" of the function la(x) and it is denoted
by the symbol:
f (p) . It (x).
The functions x", C', sin x and cos x, for instance,
have as their images
is I P P P`
and
P P 1' j,_ 1 p-'; l
from which it is to be noted that often the image is
a simpler function than the original. 'T'hus relations
between different originals can be deduced via
simpler relations between their respective images.
an der Po1 and Niessen have worked out it
great many images and front them derived new
relationships hetweenfunctions. 1lention Itas alreadti
In the course of development (if carrier telephony it was
necessary to investigate how the bcluniour of electric filters
is affected by losses. This behaviour is governed by the
Laplace differential equation. -l graphical solution of this equa-
tion, with given boundary conditions. is obtained by stretch-
ing a film of soap between three-dinn?n.ional curve, corres-
ponding to tlue boundary conditions. The case illustrated here
relates to a bandpass filter (frequency limits cut and 0)_);
k is a measure for the losses, a a measure for the damping.
been made of the problem of the aerial over the
flat earth, and for that, Lou, the symbolic calculus
was employed, with the further help of the methods
followed in the theory of the functions of a complex
variable.
These results were obtained with the aid of the
one - s i d e d Laplace integral, with the integration
extended from 0 to oo. Later, Van der P o l and
B r e m n e r went deeply into it symbolic calculus
based upon the two-sided Laplace integral
(integration from -^* to -; ). -
The space available does not permit it.-;
into details regarding other mathematical work
in connection with radio and acoustics. We can
only refer to the numerous publications by Struts
on acoustic and antenna problems, Niessen's
calculations on aerials and cavity resonators, C. J.
13 o u tv k a nt p's work on radiation properties of
antennae and acoustic and electromagnetic diffrac-
tion problems, that of F. 11. L. M. Stunipers
Philip>-Millrr tape (upper picture) in which a sound track
(10 times enlarge(l) has been eut. %% lien li_111 passes through
the tape a diffraction sprctunl is obtained (lower picture) from
which the Fourier analysis of the recorded sound can be read.
lit thi? cast- (sinu-oidal signal) the speeLrunt consists only of
components of the zero and first orders.
and Th. .1. t\ cv-crs oil frecluenc~- modulation,
'I'e II e gens studies of network synthesis. from which
the .gyrator" subsequently appeared as a new
netiyork element. and finally Kieynen's investiga-
tions of electric fields in radio valves, etc.
As regards m athetnatical and theoretical-physical
contributions outside the realm of radio, reference
is to be made to the investigations of J. Ilaringx
into problems of applied mechanics, the publications
by Bouma and C. Ilcllcr on the geometry of
colour space, and those by Niesscn on ditnagne-
tism and by Verwcy and J. Th. G. Overbeck
on the theory of lyophobic colloids.
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In the foregoing section an attempt has been
made to give a review of the scientific research work
undertaken in the period 1923-1940, and incidentally
mention has been made of the technical products
that emanated from that work.
The development of this research suffered a
check when on May 10th 1940 enemy forces in-
A
1930
air-raid warnings, etc., all tended to create an atmo-
sphere adversely affecting work. It would be wrong
to suppose, however, that scientific research was
thereby brought more or less to a standstill. On the
contrary, manyinvestigations not directly concerned
with practical applications were widened in scope
and in some fields important results were reached,
M
0 10 20 30 40 50m
Ground plan of the Physical Research Laboratory as it has been since 1942. A high-
tension room., B material-testing department, C television studio, D horticultural glass-
house, E small greenhouses with artificial climate, F one of the chemical departments,
G one of the battery rooms, II library, I installation for carrier telephony, J engine room,
K glass-blowing shop, L central workshop, M room for testing transmitting valves. The
wing K-L-M adjoins the main diagram at a-a on the right. Most of the buildings have
either one or two upper storeys.
vaded the Netherlands and shortly afterwards
Eindhoven and the Philips' works came under
military occupation.
It is not the place here to enlarge upon the course
of affairs during the period of occupation, which,
as far as Eindhoven was concerned, lasted until
September 1944. As everyone will realize, the state
of tension arising from war conditions and the
frequent acts of injustice, coupled with more direct
causes such as scarcity of foodstuffs, clothing and
means of transportation (bicycle tyres), and further
a number of air attacks on the works, repeated
though care was taken to keep them secret from
the occupying forces. The long working hours
imposed by the enemy administrators were further
turned to use for the exchange of experiences in
all sorts of domains by organizing lectures, courses
of instruction, etc.
After the liberation of Eindhoven in 1944 it
took some time before a return to normal conditions
could be established. In the first half of 1945 the
northern half of the country was still in enemy occu-
pation and even after its liberation there was no
regular contact with the rest of the country owing
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to the lack of railway communications. In order
to help university students. ti%Itlt permission of the
government in February 1913 a temporary- academy
was set up at E,indhoven where it large number of
Philips' scientists assumed slue role of professor,
and this continued up to November 191.5.
In this connection it may? be well to point out that
relations between the Philips laboratory- and the
higher educational authorities have never been
confined to that special occasion. Long before that
there had developed in the course of time it more
tricted. The publication of Philips Technical
Review, begun in 1936, had to be stopped in 1942,
and publications in the Dutch journal "Physica"
could only be made in the native language.
It was not until 1946 that journals and books
began to come into the country again from abroad.
On 1st January 19.16 Philips Technical Review
appeared again. Meanwhile, in October 1945, the
first number had been issued of it new publication
under the name of Philips Research Reports,
containing scientific articles which bear a decidedly
Department for analytical chemistry in the new part of the Physical Research Laboratory (1950).
pYR -fie intimate relationship between the labora- Philips character or which owing to their volume
is e elsewhere. Furthermore
part of the material suitable for publication which
University at Delft, partly on account of the fact
that quite a number of scientists have in had been collected during the years 1940 to 1945
course of time left our laboratory to take up a was published in book form.
professorship. Meanwhile the aced of more space was being felt
During the occupation one began to feel more and in the laboratory, which in 1929 had already under-
more the lack of literature from the outside world, gone a considerable expansion increasing ten-fold
so that as far as scientific work was concerned the amount of floor space originally
had the feeling of living as it were in a vacuum.
The possibility of publishing was also greatly res-
in 1923. A new wing had already been built in 1942,
for the administrative staff and the library, but
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until 1945 the latter had been housed elsewhere
owing to the risk of fire due to air attacks. In 1950
a second floor was built onto the oldest single-storey
part of the laboratory first erected in 1922, and that
new floor was destined mainly for chemical work.
In 1946 a change was made in the management
of the laboratory, Prof. Hoist, whose 25th year of
directorship had been celebrated in the laboratory
in 1939, retired from that function. As adviser to
the concern, he has still at the present day a word
to say, be it indirectly, in the course of affairs,
whilst at the same time he is devoting himself to
the interests of the Technical University at Delft,
where he holds of the Presidency of the Board
of Governors. The direct management of the Philips
laboratory was placed in the hands of a triumvirate
formed by the physicist Prof. Dr. H. B. G. Casimir,
the electrotechnician Jr. II. Rinia and the chemist
Dr. E. J. W. Verwey.
For reasons which will be understood, in this
section it will not be possible to do full justice to
all the research work which has been undertaken
in the Philips laboratory in the course of the last
decennium and which, in part, is still in progress.
Neither will it be possible to mention the names
of all those engaged in the various investigations
in the laboratory.
More so than in the preceding sections, here atten-
tion will be paid to materials and products and their
applications.
It has been seen that in the period 1923-1940
scientific interest was directed for a large part
towards gases, particularly as carriers of electric
discharges. In addition, in various ways more and
more interest came to be taken in solids. Mention
has already been made of the investigation of thin
crystal layers adsorbing foreign atoms. Activity
in the field of radio demanded a closer study of the
dielectric properties of glass and other insulators.
For illumination engineering, too, glass had become
an important material, as a result of the demand,
for instance, for ultraviolet-transmitting glass and
for intermediate glasses for combining glass with
quartz glass. For the fusing of glass to metal suitable
kinds of glass and alloys were required. In the tech-
nique of lighting fluorescent substances came to
be applied more and more, so that the phenomenon
of luminescence had likewise to be studied in the
laboratory. Further, attention has also been drawn
to magnetic materials, such as magnet steels and
ferrites.
Generally speaking it may be said that round
about 1940 interest was centred upon solids and
the problems relating to the solid state, both from
the point of view of purely scientific investigations
and in respect of practical applications. In the follow-
ing a number of materials will be briefly dealt with,
but since it will be mainly the results that will be
brought forward it is well to point out once more
that in many cases these results are due for a large
part to purely scientific research. As an example
may be mentioned the investigations into "induced
valency", which led to improved methods of
preparing semi-conductors and luminescent materi-
als, and the insight gained into the structure
of "sp i n e l s", which resulted in a greater variety
of "Fcrroxcube" products.
Luminescent substances
The investigation of luminescent substances
begun about 1935 led not only to the results already
mentioned but also to a wider knowledge of lumines-
cent tungstates and molybdates and of some acti-
vators such as Mn, Ti and U in different states of
ionization.
Of particular practical importance were the
silicates activated with Ti and magnesium arsenate
activated with tetravelent manganese. With the
latter substance, which shows a strong red fluores-
c.-ncc, it is possible, for instance, to improve con-
siderably the colour of the light from the small
high-pressure quartz mercury lamps.
The investigation of sulphides gave a better
insight into the part played by "fluxes", such as
NaC1, used in the preparation of luminescent sub-
stances. It appeared that it is the Cl--ions that
make it possible, for instance, for monovalent
Cu"F-ions to be "built into" the lattice. The same
can be reached by introducing into the lattice,
which consists normally of bivalent ions Zn++
and S--, trivalent cations such as Als+.
Results were also achieved in respect to lumines-
cence brought about by bombardment with cathode
rays; a deeper insight was gained into the phenome-
non of saturation with increasing current.
For some purposes, such as radar, it is not the
fluorescence but rather the phosphorescence (per-
sistent after-glow) that is of importance. It was
found possible to obtain a fluorescent screen
with long persistence by making it in two
layers, the first of which gives a blue fluorescence
under the influence of the cathode rays, this blue
fluorescence then being suitable for producing
a green phosphorescence in the second layer.
For other purposes, such as the televising of films,
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substances with it short persistence are
desired: a "field" produced on the fluorescent screen
by an unm.odulated electron beans is itnageel onto
the, film, whilst behind the film is a photocell. This
converts the light passed through, which. is modu.
lated by the variations in density of the film, into it
signal which is passed to the transmitter.
ceramic materials (ferrite s). because these have
proved to he of great importance for high-frequency
technique (radio and telecommunications).
Of theoretical importance was the interpretation
of the losses which the magnetic ferrites show at
very high frequencies (105 to 107 cjs): these losses
were ascribed to the gyromagnetic effect
A simple hydrogen liquefar1or has Lrcn con,trueted for the examination of
solids at low temperature (21) 'K). The hydrogen gas is fed in under high
pressure and prrrooled to the temperature of liquid nitrogen, after which,
through expansion, by employing heat exchangers according to the Linde
method, it becomes partly liquid (Joule-Kclcin effect). This installation has
an output of about 2 litres liquid hydrogen per hour.
Many other important applications of lutnine.s-
cent substances which have been investigated in
the laboratory have to be passed over here.
Ceramic materials and glass
Ceramic materials are obtained by sintering
together small particles which in themselves have
a crystalline structure. We do not refer Mere to
the more common materials like porcelain. steatite.
etc., about which little research work has been clone.
but to special materials, as for instance those with
a high dielectric constant, such as rutile (TiO.,), and
titanates such as 13aTiO.{. With which important
work has been done in recent. years.
Particular mention is to be made of the magnetic
prophesied by Landau, and this conception was
confirmed experimentally.
Of practical importance was the resultant know-
ledge gained of the fact that the less the initial
permeability of the substance in the low-frequency
range, and thus the greater its crystal anisotropy,
the higher is the frequency at which the gyromag-
netic losses become perceptible.
The terrific materials. which combine great
hardness and relatively light weight with a very
small electric conductivity and favourable magnetic
properties. such as low losses in a wide frequency
range, are now being manufactured by Philips
under the name of "Ferroxcube" in various compo-
sitions.
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 C.PyRnwl
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In addition to the ferrites, of equal importance colour or which, on the other hand, very readily
are the ceramic semi-conductors, which will be change colour, and glasses which are transparent
dealt with below in a separate section devoted to to ultra-violet radiation.
semi-conductors.
Improved quality and saving of space are important advan-
tages of the magnetic material "Ferroxcube" as compared wiLh
metallic magnetic materials. Left: can containing a bandpass-
filter coil for carrier telephony, the core of which consists of
nickel-iron wires and the jacket of dust-core material. The can
is necessary on account of the small effective permeability of
the dust-core material. Quality factor Q = 220 at 60 kc/s,
volume 210 cm3. Right: coil with core and jacket of "Ferrox-
cube", Q = 600 at 60 kc/s, volume 41, cros.
Glass is a material of fundamental importance
for the manufacture of incandescent lamps and
radio valves. Apart from the obvious physical prop-
erties, such as the softening point, coefficient of
expansion and specific gravity, there are many
other properties to be considered, such as the di-
electric constant, dielectric losses in high-frequency
electric fields, electric conductivity, spectral trans-
mission, etc. Considering the large number of in-
gredients from which glass is mostly made, and
consequently the numerous possible variations in
composition, it would seem to be an almost impossi-
ble task to gain a clear insight into the effect of
the composition of a glass upon its physical proper-
ties. Yet in recent times considerable success has
been attained in this direction, particularly due
to the better theoretical knowledge acquired as
a result, i.a., of the work done by Zachariasen.
It is now possible to form an idea of the internal
structure of glasses and from that to predict their
properties. Even though the reality proves to be
more complicated than the theoretical model,
the latter anyhow points the way to approximating
the correct relations of the phenomena and for
investigating those relations which are most prom-
ising for gaining the insight desired.
In cooperation with the glass works the following
practical results have been obtained: soft glasses
with small dielectric losses, glasses which have small
dielectric losses independent of frequency, glasses
which under the influence of X-rays do not dis-
Metals
Metals form an important and extensive group
of materials. The investigation of tungsten and
molybdenum and of metals like titanium, zirconium,
hafnium and thorium has already been mentioned,
as also that of alloys such as chrome-iron.
The investigation of in a g n e t s I. c c l s has likewise
already been referred to. The very important
"Ticonal" (an alloy of iron, titanium, cobalt, nickel
and aluminium) with a high value of the product
(BII)max and great coercive strength, was further
improved by making it anisotropic by cooling in
a magnetic field or by some other means.
The nickel-iron with anisotropic structure ob-
tained by rolling, for use in loading coils, has also
been mentioned elsewhere. Extensive investigations
have been carried out as to the manner in which
the texture of this material could be influenced by
a suitable thermal and mechanical treatment.
Another group of products is formed by the weld-
ing rods, the coating of which has been the subject
of particular study. Special mention is to be made
of the new method of contact welding, for which
purpose the rods are given a special coating with
a high iron content.
It is partly in connection with this that extensive
investigations have been carried out into the dif-
fusion of gases in metals. This subject had be-
come of real importance as soon as the manufacture
of water-cooled metal transmitting valves and
metal X-ray tubes was begun, and it proved to be
of particular interest in connection with welding
problems, especially as regards the penetration
of hydrogen into the metal of the welding bead,
causing porosity, cracks and fractures. In this
connection mention is also to be made of more
fundamental research, as for instance that concern-
ing ageing phenomena such as occur, inter alia,
in welding.
The absorption of gases by metals has parti-
cularly also been studied in the case of metals
like zirconium and titanium, which are used as
getters in X-ray tubes and transmitting valves.
Incidentally reference is to be made here to the
coating of anodes of transmitting valves with
zirconium to give them a black surface with good
heat-radiating properties and also to reduce secon-
dary-electron emission. Investigations of a more
technical nature in the field of metals led to new
methods of shaping and improved methods for
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determining the properties of samples of metal.
an example of the former being the so called 6-lost
wax" casting of metallic parts of instruments and
apparatus which would be too costly if Lite ordinary
methods of processing were followed, whilst ail
example of the latter is to be found in the m i c r o-
hardness meter.
This section on metals will be concluded by a
short reference. to investigations concerning oxi-
dation and corrosion. Interesting aspects are
presented by the method of hardening alloys by
internal oxidation. A study of corrosion at high
temperatures revealed that. small quantities of
molybdenum oxide may have a harmful effect.
Investigations into the non-oxidizing property
at high temperatures and the solderability of non-
oxidizing metals were particularly of importance
in connection with the development of Llie hot-air
engine.
A peculiar feature of these materials is that often
their specific resistivity is not a property inherent
in the material, as is Lite case, for instance, with a
metal, but that it depends to a large extent upon
the antecedents, such as Lite temperature and
till- gas atmosphere applied in Lite preparation, Lite
presence or not of impurities and many other
factors.
In the field of oxidic semi-conductors some
extensive crystal-chcu.ical investigations have led
to Lite production of semi-conducting materials
answering high requirements of reproducibility
and stability. Such a material is being marketed in
various fortes as N.T.C. "resistors" (negative tem-
perature coefficient. resistors).
Much attention was paid also Lo selenium. The
resisttutce of selenium can be varied by the addition
of foreign substances. This investigation has led
to the production of rectifiers suitable for low vol-
tages, e.g. 18 V, and, by connecting them in parallel,
for high currents. On Lite other hand very small
rectifiers are being made for currents of a few
milliamperes, as used in the a.nplifving technique,
for example. for modulator cells, Which play an
important part in carrier-telephony, and in series-
connected sInall cells for rectifying high voltages.
By a certain treatment of the surface of Lite
,eletriuin and choice of Lite electrode material it is
possible, to a certain extent, to determine Lite
voltages which are to be applied per rectifying
unit.
I)iiring the years 1910-1915 there has been re-
newed interest in the crvstal rectifier, a coIn-
ponent used in the early days of radio. It appears
that in the range of ultra-short waves, which has
become of such importance, this clement in a more
perfected form offers advantages over rectifying
valves. Extensive investigations are proceeding in
the laboratory also in this field and have already led
to it rapidly increasing manufacture of various types
of crystal rectifiers.
There are indications that the possibilities of
applications in time field of semi-conductors are
not by any means exhausted, and that, by the
very reason of their abnormal properties, we are
only at. Lite beginning of a development of great
impoM,mce for electrotechnical engineering.
Between the insulators of an inorganic and an
organic nature, such as glass, porcelain, amber.
polystyrene, on the one hand and the metals as
good conductors for electric current on the other
hand, there is an important group of substances
which as compared with metals show little conduc-
tivity, e.g. iron oxides, copper oxide, selenium, ger-
manium, etc. These are of interest because the%-
possess typical properties lacking
two groups.
'T'heir principal property is a large, negative.
tentperaturc coefficient of their resistance, a proper-
ty found in practically all representatives of this
group. Sonic of theme also show photo-conductivity.
in that when exposed to light their resistance is
reduced. Others, when provided in a certain tisay
with electrodes, appear to have rectifying proper-
ties, which means to say that when Lite current
flows in one direction the resistance is many tiers,
say 1000 or more Limes less than in tl.c other direc-
tion. There are also certain materials whose resis-
tance appears to he dependent upon the electric
potential gradient.
Although these properties have been known for
it long time it is only during the last 10 to 15 years
that it has been found possible to utilize tltent.
Obviously a high. temperature coefficient of the
resistance ofliers many possibilities. Mention may
be made, for instance, of the measuring of tempera-
ture and of radiation, furthcrntore, owing to the
negative sign of time coefficient, there is Lite possibili-
ty of suppression of current peaks and application
in delay devices, regulating apparatus, etc.
This review will be concluded by referring to
some products which, have particularly come into
existence in Lill' last ten to fifteen years as a result
of laboratory work. The reader is not to expect
a catalogue with detailed descriptions. Many of the
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1.891-1951 37
products which will be mentioned have already been
described more or less fully in recent volumes of
this journal, whilst a description, of some others
will shortly be appearing in our columns. Suffice it,
therefore, to mention in a few words only the most
important products.
Sources of light
In the field of lighting we have already referred
to the "TL" lamps, which as such have already
Further, there is the low-pressure mercury lamp
without any fluorescent material but made with
a glass which is transparent to ultra-violet radiation
(2537 A), viz. the so-called germicidal lamp. Other
special sources of light are the flashlamp for the
illumination of Wilson chambers and for other
photographic instantaneous exposures, and a point
source of light in the form of a gas-discharge lamp
the light of which can be modulated up to high
frequencies.
long passed the laboratory stage of development.
Further investigations in connection with these
lamps are being carried out in regard to their colour
rendering, for instance with new phosphors used
in their manufacture. Particular mention is to
be made of the application of "TL" lamps for irra-
diating plants. Since 1949 the Philips laboratory
has had a large horticultural glasshouse at its dis-
posal, in which various plants are being cultivated,
and also a dozen smaller glasshouses illuminated
exclusively with artificial light. With the large
variety of phosphors available it is possible to
investigate how the growth and flowering of plants
are affected by the spectral energy distribution
and the intensity and duration of radiation.
Radio, television, etc.
In the field of radio conditions had already reached
such a stable state before 1940 that the normal
development of valves and apparatus no longer
belonged to the work of the laboratory, so that
attention could be directed towards new develop-
ments. In the first place mention is to be made of
the new valves for ultra-short waves (decimetric
and centimetric waves). Development of these
valves had already reached an advanced stage
abroad during the war years, so that in 1945 Philips
had a great deal to catch up with. Extensive investi-
gations had already been carried out with radio
valves in the metric wave range. Special tubes were
developed based upon the velocity modulation of
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 CPYRGHT
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Cucumbers cultivated entirely under artificial light. The light is supplied by "Ti" ,lamps.
The temperature inside is prevented from rising too high by causing tap water to flow down
the pane of glass in front of the lamps. Half-way down between the "T1' lamps is a TIN
lamp, the ultra-violet radiation from which prevents the growth of algae on the glass.
,lcctrons (the velocity-modulation valve, the
dysiron, the multireflection tube), employing a
umber of Philips' own inventions.
An important improvement of heated. cathodes
s Lite L -cathode, which contains a reservoir
illed with barium oxide and enclosed by a porous
Tall of tungsten acting as the source of electron
mission. With the aid of this cathode a disc-seal
n o d e can be built for wavelengths down to 8 cm
frith a clearance of only 40 !. between cathode and
grid. This new type of cathode offers important
possibilities for many other applications as well.
An intensive study is being made of Lite special
circuits for generating ultra-short waves, by em-
ploying cavity resonators, and of modern means
for conducting high-frequency energy with Lite aid
of wave guides.
After 1945 the development of television had to
be taken in hand again in the laboratory on account
of the greater interest being shown in it everywhere.
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 1 . YID'' , r I I
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JULY-AUGUST 1951 1891-1951
Tubes for centimeLric waves. 1~'ront left to right: a multi reflection tube with a contin-
uous output of 20 W on a wavelength of 12 cm; a receiving tube. of the "lighthouse"
shape for amplification of wide frequency bands (gain 10 at a bandwidth of 50 Mc/s,
noise figure 10 dh at a wavelength of 10 cm); a magnetron yielding pulses of 1000 kW
at a wavelength of 3 cm; a velocity-modulation valve with a continuous output of
100 W at a wavelength of 3 cm.
At first a system of 567 lines was used, with 25 frames it could quickly be changed over to different num-
per second. In the audio channel frequency hers of lines. This proved to be of great value for
modulation was applied. As a result of many judging the relative merits of various systems.
discussions on the question of the number of lines When, later on, the Netherlands Television Commit-
the transmitting apparatus was designed so that tee advised the adoption of a system with 625 lines
67074
Some 1, cathodes (with a cigarette for comparison of size). The L cathode has a porous,
metal, emitting surface and can withstand heavy loads, say 1.00 A per em2.
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 Approved For Release 1999/09/24: CIA-RDP83-00423R002000130013-1
.'It't-utt fin takiti_ inra -ur.?tnrnt - of it , (.It,( it% - mmItil it tiit t c al%r (oil thr IxIre it (- right)
at a ?a,~ lrti_tII ut 3 rni. Ilrrr ?a%r ,Inuit'. are ti-rd fur runtlurting tilt' energy.
and ?.i franc- Itrr -round Hit- irt-tallatinn %%a- ^ladr
-uitahlr fur that
Furthrr. at.trutiurt N% a, dt?cutrd hut It Iu thr
ltruhlrnr- rurunntrrrd at tltr rrcri\ i11 , 11111 and to
t.hu-t ari-in_ in the trap-nti--ion. 1- far a- rrcrlttiuu
i; runt?t?rnt?tl. ha-rd 111tun flit- rt?~ult. of rsltrrintrnt-
alrt?atl,, nu?ntiuurtl a -v-trim (d projection ti-N-N 1-1(111
v, a-',, urkrtl out \cillt the aid of' a `+rIt tit it!t ultliral
-v-tt?rn. a-irtg vrrc -tnall ltrujt-rtion tubes with
tilt -rrrrn coated No, ith ltho-lthur- suitable For tin
}turbo-r. tiltt-t?ial ltrrrautions hall to be taken
main-l di-coloratiuu (if' tht? gla,, of thrrr tuhri
unti l the influrucr of cathode ratis ant! S-ravs.
In the ulttit?al -v-lrrn Itruln?r. n-r vVa- tttatlr? of a
correction I' I a t r made of gelatin. fur ocitich a
-eltarate method of ruanufacture had Lo hr tlrvelojtrd.
I.rft: t?, I-i.,k-nli IIII1r- lur t,-leti.inn (an irrinu-nlir anti an iIII tgt'
Ii i_It t: it Ii i r t it rr t it Itr tnr ttrujr?rtion tclr, i-inc
Apprnvnrl I r%r Rnlnncn I QQQIf1Q/9A ? (1 A_Rr1DR4_fflA94RfG9=013013.4
^"t
 CPYRGHT
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Of course attention had also to be paid to direct-
view reception. One of the most important results
of the work done in this connection was a consider-
able improvement in regard to flicker of the image
by employing phosphors having a long persistence.
As regards TV transmission the most important
advance made was in the construction of new
pick-up tubes based on the principle of the image
iconoseope. Further improvements lay in the
television cameras and in the studio lighting.
Except for some short interruptions there have
been regular experimental television transmissions
from Eindhoven ever since 1946, for which purpose
a studio, a control room and dressing rooms for
artists were fitted out in the laboratory building.
These experimental transmissions have helped
much towards arousing the interest now being
shown in this youngest branch of technical develop-
ment both in the Netherlands and in adjoining
countries.
Next in order to radio and television is the work
done in the field of telecommunications.
Ever since 1935 there has existed a department
in the laboratory (organically not belonging to it
but as part of the A.F. telephony department of
the works) where apparatus for carrier telephony,
i.a. a 17-channel system, and for A.F. telegraphy
have been developed. About 1940, in cooperation
with the laboratory, a modern carrier-telephony
system for 48 channels was developed,
in which the new core material for coils,
"Ferroxcube", plays an important part.
This system is already being used on
an extensive scale in the Netherlands
and in Switzerland, whilst it is to be
installed also in Denmark in the near
future. In this connection a word of
grateful recognition is due to the
Netherlands P.T.T. officials for their
close cooperation. In 1945 the carrier-
wave department was transferred from
Eindhoven to the Philips' Telecommuni-
cation Industry at Hilversum, whilst a
research group for telecommunications
was established in the laboratory.
Development work in Ililversuni is
proceeding further in the direction of the
improvement and reduction in size of
electrical and mechanical parts, with the
aid of results reached in the laboratory.
Special carrier systems have been
developed which are suitable also for
short distances. Further, by developing
through-filter and other filters, the laboratory
has already contributed much towards a system
now in course of development at Hilversum
for incorporating some hundreds of channels in a
coaxial cable.
In this laboratory work is continuing on new
methods of modulation; for instance, a simplified
form of pulse-code modulation has been studied,
the quantum modulation, which makes it possible
for conversations to be carried satisfactorily over
long distances in spite of a high noise level. In
addition, the possibilities of applying new materials
and components for telecommunication apparatus
are being studied.
In this connection mention is to be made of the
new switching tubes with ribbon-shaped electron
beam, which promise interesting applications in the
field of telecommunications and electric computers.
Special mention is to be made of the system of
facsimile transmission worked outinthe labora-
tory, by means or which documents can be transmit-
ted and photographically recorded at the rate of
5000 cm2/minute.
Of importance for meteorology is a newly devel-
oped radio sonde, in which extremely small radio
valves with low current consumption are employed
and with which experiments are now being carried
out in conjunction with the Royal Netherlands
Meteorological Institute at Dc Bilt.
such things as repeaters, a super-group Dr. A.F. Philips in front of the camera of the Eindhoven television transmitter.
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A product w- IIicI I certainh ha- -onto crrnnr'ctiun the lri-tun of une cdinder i- caused to act as Hie
with ra(lio. ennridcrinr the jived of it ul)ltly -ourcc tran-iu r 1u-tort for another. i- of intltortancc in
in place- w hcrc no rdcciricitv i- av ailahlt.. but which cortnectiort with 1nture lro--ihilitie- tin' curt-etluencs~s
represent- the outconu? of a dctcinluncnt of it- uf' which ran utt Net. he falh predicted.
own. i- tlic air eit t;irtc already rcfcrrcrl to in thi -
rcview. From it clo-c -1nth of the kcal e chan~?,.
hetssecn flowing ga-e- anti metallic wall- and of
utatcrial- - uitalde I herefor. arid further of, the
therrno-d, nantic- of tlo-v-\ r1r. it ha- ltccontc lto--ihlc
to build a li ht hint--peed rnttur with frond tIli- anal
efficienct. 1 to ws principlc_ ufapplicatioufor-~-tcnt-
with more titan one c,,lindr?r_ according; to Ntiltich
III the lield of acuu-tics there are rloite a numLer of
ncvti product - in he no - ntionerl. F it-t of all late itn-
lrrolcti -ountl rclrrvolut?tinrt by tuean- of' -tereu-
I'lrons. \tihich ha- led aLu to the curt-trrtctiort of
,mill nrierolrhone-. The ideal nicrophune.witlt -mall
dintco-ions compared vcilh the vrtv-clcniZth. al.o for
iti`h audio-frcrlut?ncie appeared to he nut-t clo-eh
apprurimatcd by the coudcit -cr uticJ. ophune
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Taking measurements in the testing of an experimental air engine. Energy input by
electric heating, energy output via a loaded dynamo. Connected to the desk on the left
are therrno couples measuring the temperature at various points (inside and outside).
A Farrthoro pressure indicator records the pressure in the cylinder as a function of time;
the phase of this diagram is checked with the aid of a capacitive pressure indicator (con-
nected to an oscillograph) and a stroboscope.
Hall for acoustical investigations (i.a. stereophony) and large-screen television (almost
3 m X 4 m).
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which can Hutt be rood' Ili it size of' about 20 ruin.
and for special purpust- ex-en as small it- T min.
In Lhe Philip- laboratory the nett'--art attestion
has also iccn paid to the dctrloprtrcut. -tartttl in
Denmark. of the nta g rt e t o p h o nt for recording
and reproducing -ound. Thi- tttltloprn?ut ohligtd
the manufacturer- of gr:nophonc record, at last
to relintlui-h tlo? tb?nrand that it -built{ be po-sihle
to play their record- both elctLricahIv and mtchanit-
audibility. Icd further to tic designing of a vector
cardiograph. some specimens of which have hecn
gittu to nu?dical experts for testing.
1no01g the i-rav tilts titre is it net, one for
contact tit(-rapt and. further. note high-powered
Iuhc- for \ - rat (Ii fir action with accessorv
apparatus.
ally. as it rt=ult of tshu It to j. intprot ernenI.-
hetame po"iilc in the fit-ill oftltttrital gramophone
reproduction It,. urtau- of ntirrourroot t rctord