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JOSEPH SLEPIAN
February ~ I, ~ 89 I -December ~ 9, ~ 969
BY T. KENNETH FOWLER
OSEPH SLEPIAN, INVENTOR of the ignitron and other main
stays of the electric power industry, after a lifetime ca-
eer at the Research Laboratories of the Westinghouse Electric
Corporation, cliecl on December 19, 1969. Electecl to the
National Academy of Sciences in 1941, STepian was a mem-
ber of Section 3l, now callecl Engineering Sciences. IncleecI,
his career exemplifiecl the union of these clisciplines.
Hoicler of 204 patents at Westinghouse, STepian began
his career as a pure mathematician. He was born in Boston
on February Il. IS9l, son of Russian immigrants. Advance cl
student status in high school allowed! him to enroll at Harvarc!
University at age 16, he macle Phi Beta Kappa en cl received
his bachelor's degree in 1911, his master's degree in 1912,
en c! a Ph.D. in mathematics in 1913. All cluring this time he
maintained odd jobs to help support himself, including a
stint as a licensecl motorman on the Boston Electric Rail-
way.
After Harvard Slepian was able to continue a year of
postcloctoral studies as a Shelclon fellow, first at the Univer-
sity of Gottingen in Germany en c! then at the Sorbonne in
Paris. He returned to the Unitecl States in 1915 en cl ac-
ceptecl a position as instructor of mathematics at Cornell
241
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242
B I O G RA P H I C A L
EMOIRS
University. After only a year at Cornell he resigner! his posi-
tion to join the Westinghouse company at its East Pitts-
burgh Works as a student apprentice in the railway motor
department. By 1917 the company had moved STepian to
the research department, shortly before the establishment
of its pioneering inclepenclent research facility at Forest Hills
in 1918. He advanced quickly, as head of the General Re-
search Section in 1922, research consulting engineer in 1926,
en cl associate director for research from 1938 until his re-
tirement in 1956.
Slepian's move to Westinghouse proved a happy transi-
tion for all concerned, his prolific output of patentable
inventions for the company being exceeded only by those
of George Westinghouse himself. According to colleagues
Slepian macle maximum use of his mathematical talents in
his new career, his inventions invariably being the conse-
quence of careful science en cl theoretical analysis. In fact
his talent for invention hacl aIreacly emerged at Cornell,
where in 1915 he filet! a patent for a crevice to measure the
speecl of a boat by means of magnetohyciroclynamics. By
1919 he hacl proclucecl his first patent at Westinghouse, for
circuit interrupters. He was still pursuing inventions when I
first met him, late in his career, when he was cleveloping a
new plasma method of isotopic separation, his ionic centri-
fuge that he pursued before en c! after retirement, with 20
publications on this topic alone, most of them in the Pro-
ceeclings of the National Academy of Sciences.
STepian's first major success at Westinghouse lee! to the
autovalve lightning arrester, at a time when the cost en cl
maintenance of conventional electrolytic arresters no longer
server! the neecis of a growing industry. His pioneering re-
search on lightning arresters began in 1920, three years
after his transition to a career of engineering research. Char-
acteristically, when presenter! with the problem, STepian first
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fOSEPH SLEPIAN
243
concluctec! a thorough analysis of the operation of electro-
lytic lightning arresters during a discharge research that
clisclosecl the neecl for surge protection that he wouIcl solve
with a countervoTtage proclucec! by a glow discharge in air.
This in turn lecl to his many experimental en cl theoretical
contributions to the fielcl of electrical concluction through
gases en c! a familiarity with plasma physics that inspirer!
even his later work on the ionic centrifuge. Slepian's care-
ful stucly of ionized gases also prepared the way for other
notable inventions, inclucling the cleion circuit breaker en c!
the workhorse ignitron mercury rectifier familiar to me from
my earliest contact with laboratory experiments on plas-
mas.
Slepian's contributions to the ignitron followocl a pat-
tern establishecl in his work on arresters. Though aIreacly
commercial, mercury rectifiers hac! reacher! an impasse:
unacceptable "arc-backs" that required creep analysis to un-
ravel. Slepian proviclecl this analysis, leacling him to pro-
pose separating the multiple rectifier anodes into individual
chambers, which was the first step toward the ignitron cle-
sign. There followocl an intensive period of research to pro-
vicle a means of extinguishing en c! then initiating anew the
mercury arc on each operation cycle, clepenciably, when
required, without appreciable time lag. More than 4 mil-
lion kVA in ignitrons hac! been installer! by the late 1940s.
The clelon circuit breaker was also the result of cletailecl
scientific research, in this instance on the nature en cl ori-
gin of arcs. As in his other research his work always in-
volvecl observation en cl experiment as well as theory. Though
first a mathematician Slepian hacl also become a productive
and careful experimentaTist in the laboratory. It was he who
discovered plasma arc regimes not requiring thermionic
emission of electrons from the cathode, at gas densities
well below those thought possible before his work on cold-
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244
B I O G RA P H I C A L
EMOIRS
cathode heavy-current arcs. The practical result was the cleion
circuit breaker, employing the coIcI-cathocle technique to-
gether with ingenious annular electrocles en cl voltage clistri-
bution that avoiclec! thermionic hotspot emission that wouic!
otherwise spoil the almost instantaneous builclup character-
istic of the coIcI-cathocle operating regime.
A highlight in STepian's career was his receipt of the
Edison Mecial in 1947, in part for his inventions of the
autovalve lightning arrester, clelon circuit breaker, en cl ig-
nitron cites! above. Marveling that a one-time pure math-
ematician wouIcl receive an award honoring a man like
Edison, Slepian in his acceptance speech reflected wisely
on the productive interplay of mathematics, science, en c!
engineering. It is appropriate to quote here excerpts from
his remarks, publishecl in full in Electrical Engineering
(67~1949] :258-61~.
That a man with my particular kind of talents, abilities and personality
should win a high engineering honor may seem very remarkable.... The
dominant interest of my youth, and the kind of formal education it led me
to acquire, certainly did not presage distinction in such fields.
I have pondered on what rightly may be called the really distinctive fea-
tures of the mathematician, scientist and engineer. There seem to be two
ways of logically distinguishing among them. One . . . is by the kinds of
skills they display . . . their crafts. The other, and which I think strikes
deeper, is by their motivations or compelling interests.
Let me proceed then to ask these questions. When the mathematician is
doing that which is uniquely mathematics, and cannot possibly be said to
be physics, or chemistry or other science; when the physicist, as a typical
scientist, is doing that which is uniquely physics and cannot be said to be
mathematics or engineering; when the engineer is doing that which is
certainly engineering; what are their respective distinctive motivations and
compelling interests?
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fOSEPH SLEPIAN
My answers lead to the following definitions.
245
The "mathematician" is one whose interests and activities lie in determin-
ing and studying how things may fit together, that is, what are possible
systems of order, and what are the details of such possible systems of order.
The "scientist" is one whose interests and activities lie in determining what
is the actual order of things in the physical world and studying the details
of that order.
The "engineer" . . . is one whose interests and activities lie in devising,
designing, constructing or controlling the operation of physical devices,
machines, technical processes, or services which have practical utility . . .
[making] use of the accumulated knowledge, skills and techniques of the
"mathematician" and the "scientist."
We know now that while "mathematicians" and "scientists" carry on their
activities for "their own sake," that is for aesthetic reasons or other intellec-
tual satisfactions, nevertheless, their work will lead to radical and revolu-
tionary advances in technology in the future. The invention of the number
system in which all algebraic equations, including x2 + 1 = 0, have solu-
tions, had to be done by the "mathematician." The "engineer" could not
anticipate its utility for solving practical A-C problems. Only a "physicist"
would be engrossed with the faint glows given off by certain rare minerals.
How would the "engineer" know that these faint glows were the indications
of tremendous technically utilizable forces within the atom?
With these examples before us, we see that while there are also other
important reasons, we must support "mathematics" and "science" in the
United States because of the inevitable future advances in technology which
they will induce. To make "mathematics" and "science" flourish, we must
create for "mathematicians" and "scientists" a favorable atmosphere.
High above all other requirements in the favorable atmosphere is that of
freedom; freedom to choose their work or object of interest, freedom to
write and publish, freedom to communicate with their fellows.
Slepian fount! his own favorable atmosphere at the
Westinghouse Research Laboratories, a moclel for other cor-
porations at the time the Forest Hills laboratory was cre-
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246
B I O G RA P H I C A L
EMOIRS
atecI. "Sometimes," he wrote for his twenty-fifth class re-
union at Harvard, "I look with envy at the apparently more
leisurely en cl less harassed lives of acquaintances in univer-
sity circles, en c! at one time I nearly changer! over to this
fielcI, but on the whole I think I am in the work en cl place
best suited to me . . ."
Besicles his own research en c! inventions STepian was a
valuccl consultant, much sought for his acivice by others in
the company. During WorIcl War II he both participated in
the Manhattan Project en c! server! as consultant to the Of-
fice of Scientific Research en cl Development, en cl as a clol-
lar-a-year man with the War Procluction Board.
Despite leaving academia as a profession STepian never
lost interest in teaching, fulfi~lecl at Westinghouse by his
own initiative in organizing informal courses on a variety of
topics, inclucling vector analysis, the theory of electricity
en cl magnetism, the kinetic theory of gases, en cl the con-
duction of electricity through gases. In addition, besides
practical inventions, in 1922 he filet! for a patent, issued in
1927, for the iclea of accelerating electrons by magnetic
incluction, later employocl in the betatron accelerator cle-
velopec! by DonaTc! Kerst at the University of Illinois en c!
usecl wiclely in nuclear physics research.
Slepian published 121 technical papers, articles, and es-
says, some of which are listen! below. In 1933 Westinghouse
Electric Company published his book, Conduction ofElec-
tricityin Gases, a compilation of his lectures for Westinghouse
colleagues. This book became a classic, user! by physicists
and educators throughout the world.
In aciclition to receiving the Edison Mecial in 1947, Slepian
was the recipient of the John Scott Mecial at the Franklin
Institute in 1932 en cl the American Institute of Electrical
Engineers' Benjamin Garver Lamme Mecial in 1942. He was
elected! a fellow of AIEE in 1927 en c! the Institute of Radio
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fOSEPH SLEPIAN
247
Engineers in 1945 Predecessors of the Institute of Electri-
cal en cl Electronic Engineers). He received the Westinghouse
Order of Merit in 1935. In 1939 his scientific contributions
were recognizes! by the French with the title Officer cle
Acaclemie. In 1949 he was awarclecl an honorary cloctor of
engineering degree by Case Institute of Technology (now
Case Western Reserve) en c! in 1955 an honorary cloctor of
science by the University of Leecis.
At the Lamme mecial ceremony L. W. Chubb, then
Westinghouse director of research
I, painted a charming pic-
ture of the young mathematician turned engineer.
When he first arrived at the engineering laboratories, I happened to be in
charge and in a position to recognize his unusual qualities.
On one occasion the rest of us were so busy on some development that I
could not assign Doctor Slepian to a new job at the moment. Instead of
marking time until we finished, Slepian asked my permission to study a
complicated setup of large motors, electrolytic condensers, reactors, instru-
ments, transformers and disorderly wiring and cables in a nearby room.
Permission granted, he traced the circuits and made a complete schematic
diagram of the system on a large piece of paper. He did not recognize the
electrolytic condensers, and I explained them to him.
Without further assistance, he deduced that the setup was designed to
explore operation of polyphase induction motors from a single-phase power
line. He not only learned about this specific problem but went on from
there, in a short period analyzing the general problem of phase conver-
sion, and making several inventions for both static and rotating phase split-
ters. His initiative and independence have not lessened during the years
since then.
Slepian suffered a stroke in 1951, but though handi-
capped by health problems, he continued at the Westinghouse
laboratory until his retirement on February 2S, 1956. In
private life he lovecl music, art, en cl literature. He was a
season ticket holder for the Pittsburgh Symphony Orches-
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248
B I O G RA P H I C A L
EMOIRS
tra for over 40 years. He likes! to joke, en c! his friencis en-
joyocl his incisive sense of humor.
He married Rose Myerson in 1918. They hacl two sons'
Robert en c! David, both of whom follower! with distinction
in their father's footsteps, Robert at Westinghouse en cl David
at Bell Laboratories. David was electecl to the National AcacI-
emy of Sciences in 1977.
I WISH TO THANK Joseph Slepian s son David for his help and com-
ments. I also gratefully acknowledge the help of John Coltman, who
was well acquainted with Joseph Slepian at Westinghouse, and F. A.
Furfari for his help in resolving several questions. I have drawn
liberally from Furfari's biographical article about Slepian in IEEE
Industry Applications Magazine (November/December 2000) and from
published comments by M. W. Smith at Slepian's Edison Medal
ceremony and L. W. Chubb at his Lamme medal ceremony.
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fOSEPH SLEPIAN
SELECTED BIBLIOGRAPHY
1919
The flow of power in electric machines. Electr. I. 16:303-11.
1920
Reactive power and magnetic energy. Trans. AIEE 39:1115-32.
1921
Why high frequency for radiation? Electr. I. 18:129-31.
1923
Surges on power systems. Electr. I. 20:176-81.
1926
249
Theory of current transference at the cathode of an arc. Phys. Rev.
27:407-12.
Thermionic work function and space charge. Phys. Rev. 27:112(A).
1929
With R. Tanberg and C. E. Krause. New valve-type lightning ar-
rester, Electr. World 94:1166-67.
Theory of the deign circuit breaker. Trans. AIEE 48:523-27.
1930
Theory of a new valve type lightning arrester. Trans. AIEE 49:257-
62.
1931
With R. C. Mason. High velocity vapor jets at cathodes of vacuum
arcs. Phys. Rev. 37:779-80.
1932
With L. R. Ludwig. Backfire in mercury arc rectifiers. Trans. AIEE
51 :92-104.
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250
B I O G RA P H I C A L
1933
EMOIRS
With L. R. Ludwig. A new method for initiating the cathode of an
arc. Trans. AIDE 52:693-98.
1936
The ignitron: A new mercury arc power converting device. Trans.
Am. Electrochem. Soc. 69: 399-414.
The ignitron. Electr. I. 33:267-72.
1937
With R. C. Mason. The experimental validity of Paschen's law and
of a similar relation for the reignition potential of an alternating
current arc. 7. Appl. Phys. 8:619-21.
1938
With A. H. Toopfer. Cathode spot fixation and mercury pool tem-
peratures in an ignitron. 7. Appl. Phys. 9:483-84.
1939
With W. M. Brubaker. Experiments on the condensation rate of
mercury vapor. Phys. Rev. 55:1147 (A) .
1940
With W. E. Berkey. Spark gaps with short time lag. J. Appl. Phys.
11:765-68.
1941
With W. E. Pakala. Arcbacks in ignitrons in series. Trans. AIDE 60:292-
94.
1942
Energy and energy flow in the electromagnetic field. J. Appl. Phys.
13:512-18.
1950
Electromagnetic ponderomotive forces within material bodies. Proc.
Natl. A cad. Sci. U. S. A. 36:485-97.
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fOSEPH SLEPIAN
251
1951
Lines of force in electric and magnetic fields. Am. f. Phys. 19:87-90.
1955
Failure of the ionic centrifuge. 7. Appl. Phys. 26:1283.
Isotope separation by ionic expansion in a magnetic field. Proc.
Natl. A cad. Sci. U. S. A. 41:4541-57.
1957
The magneto-ionic expander isotope separator. 7. Franklin Inst. 263:129-
39.
1958
Hydromagnetic equations for two isotopes in a completely ionized
gas. Phys. Rev. 1 12: 1441-44.
Representative terms from entire chapter:
circuit breaker
