Hendrik van der Bijl

Hendrik van der Bijl
Pretoria, South Africa
Death date
Associated organizations
Royal School of Technology, Dresden, Western Electric
Fields of study
Electron theory


Hendrik Johannes van der Bijl was born in Pretoria, South Africa, on November 23, 1887 to a prosperous farmer. He was the fifth child in a family which eventually grew to eight. Their South African origins dated back to 1668 when Gerrit van der Bijl arrived at the Cape from Holland to serve the Dutch East India Company. During van der Bijl’s childhood, Pretoria was the capital of President Kruger’s South African Republic, an area also known as the Transvaal.

The Anglo–Boer War started when van der Bijl was 12 years old. His family remained in Pretoria until the city was occupied by the British in mid 1900, when his moved to the Cape, where van der Bijl was able to complete his schooling while removed from the war. After graduating from Franschhoek High School he spent three years at Victoria College (now the University of Stellenbosch). Here he received the B.A. degree in physics, the third person to do so from the university. Van der Bijl also won a college prize for physics and the van der Horst Prize for the most deserving student of mathematics and physical science in the college.

Studying in Germany

Van der Bijl spent a semester at Halle University studying philosophy and inorganic chemistry. His he moved to Leipzig to work under Professors Wiener, des Coudres, and Jaffe, who had impressed him by their work. By March 1912 he had successfully completed a Doctorate on the behavior of ions produced by a strong radium source in selected liquid dielectrics. Wiener recommended van der Bijl for a Physics Assistant post at the Royal School of Technology, Dresden, generally reserved for German students and required the incumbent to remain in the position for at least two years. However, he managed to persuade the authorities to take him on for only one year (or longer if he so desired).

The Head of the Department of Physics at Dresden was Prof. Hallwachs, who had done much of the early research on the photoelectric effect. In 1900 the German physicist Planck had proposed the Quantum Theory to explain the mechanism of absorption and emission of electromagnetic waves by resonators of atomic or subatomic dimensions. In 1905 Einstein applied the Quantum Theory to the photoelectric effect and proposed a linear relationship between the wavelength of the light and the maximum velocity of electrons emitted from the irradiated metal. Quantum mechanics had not yet been widely accepted by the scientific community, and this relationship was seen as a means to test its validity. Several attempts to do this had already been made but all they had achieved was to convince the doubters that the Quantum Theory should be abandoned. Hallwachs brought this problem to van der Bijl’s attention and suggested that he look into it.

Work On The Photoelectric Effect

At that time the apparatus usually chosen to determine the maximum velocity of emission consisted of an irradiated photocathode and an anode with a metallic grid interposed between them. Both the anode and the grid had a central hole to allow the light to reach the photocathode. Electrons emitted by were drawn to the anode through the grid . The negative potential on the grid was then raised to the point where the anode current was cut off, and this was taken to be the maximum velocity (measured in volts) of electrons emitted by the photocathode. It was generally accepted that the plane containing the grid would provide a uniform equipotential surface which could be varied by changing the voltage.

To satisfy Einstein’s equation, the maximum electron velocity should be in the region of a few volts, but most workers had found grid voltages more than ten times greater. Van der Bijl suspected that the field due to the relatively high anode potential penetrated the grid and produced a “stray field” between the grid and the cathode. He designed a special version of the photoelectric tube which allowed the distance between the grid and the anode to be preset to convenient values. The distance between the cathode and the grid could be changed while the tube was under vacuum to facilitate measurement of the contact potential between the grid and the cathode. With this apparatus he was able to find the combinations of grid and anode voltage which would just reduce the anode current to zero for various distances between the anode and the grid.

The relationship is clearly linear, and by extrapolating it to the vertical axis the inferred grid voltage corresponding to zero anode potential was the same for both spacings (about 4 V). Under these inferred conditions the influence of the anode-grid field on the grid-cathode field being removed, the true retarding potential depended only on the cathode-grid potential. In this way he eventually reached voltages which came close to the value satisfying Einstein’s photoelectric equation. He concluded that the field between the anode and the grid penetrated the grid and that its effect on the cathode-grid field was proportional to the anode voltage.

Professor Millikan

One of the leading specialists in electron theory was Robert Millikan, a Professor of Physics at Chicago University. Millikan had also been trying to satisfy the Einstein photoelectric equation using an apparatus similar to that used by van der Bijl. His unsatisfactory results had turned him into “an avowed opponent of light quanta and was trying to prove Einstein wrong”. Soon after van der Bijl had completed his experimental work, Millikan came to Germany to read a paper relating to his discovery of very high-emission velocities. Subsequently he paid a visit to Dresden and van der Bijl (possibly because he spoke English) was given the job of showing him around. During the course of the visit, they compared notes and found that his extraordinarily high velocities were due to the same cause, viz.: the stray field.

Millikan thereafter changed from being an opponent of Einstein’s photoelectric theory to become the man who eventually proved Einstein’s equation to be correct. In 1916 Millikan published the results of his subsequent experimental work which fully justified Einstein’s photoelectric theory. This paper gives a more rigorous confirmation of Einstein’s theory than the work done by van der Bijl, and as the apparatus used did not require a grid he did not make use of van der Bijl’s stray field relationship. Millikan does not acknowledge van der Bijl’s paper and van der Bijl nowhere refers to Millikan’s subsequent work, but it seems clear that, at the very least, van der Bijl’s work must have moved Millikan to return to the problem and finally find the solution.

Millikan was at that time Technical Adviser to the American Telephone and Telegraph Company and was aware that their subsidiary, the Western Electric Company, was negotiating for the rights to use de Forest’s Audion as a telephone amplifier. He could see that van der Bijl’s investigation was not only relevant to the Quantum Theory but also to the thermionic vacuum tube.

On March 20, 1913 he wrote to Millikan asking for help in finding a suitable research position at one of the American universities. Millikan showed van der Bijl’s letter to Colpitts, a senior research engineer at Western Electric (best known for his oscillator circuit) with the suggestion that they should offer van der Bijl a position in their laboratories. Colpitts wrote to Dresden on May 28 suggesting that van der Bijl should visit them in New York to see whether he might like to join their industrial research team. By the time the letter reached Germany, van der Bijl had already left for Chicago. In July, Frank B. Jewett, Assistant Chief Engineer of Western Electric, met van der Bijl in Chicago and offered him employment in their Research Department at a starting salary of $36 a week. Van der Bijl presumably spent some time vacationing before joining the Western Electric Laboratories in September 1913.

Western Electric

When Van der Bijl joined the company he recognized that the thermionic triode was very similar to the photoelectric tube he had used in Dresden. He developed the stray field relationship which he had discovered in Germany and the factor, became the amplification factor. Together with the anode resistance and transconductance, these remained the basic amplifier parameters until the transistor took over after World War II. With his team he investigated the effects of electrode spacing and grid proportions on tube performance making it possible to design tubes for particular purposes. His 1919 classic paper, "Theory And Operating Characteristics Of The Thermionic Amplifier" sets out his analysis of vacuum tube behavior in detail.

His first tube was the type M, or 101A designed for use as a telephone line amplifier and the first Western Electric tube to be provided with a base mating with a mounting socket to facilitate replacement. Late in 1909, during talks with the management of the Panama-Pacific Exposition due to open in San Francisco, CA, in 1914, Vail and Carty, two senior executives of the company, had virtually promised that they would have a telephone working between New York and San Francisco in time for the opening of the exhibition. Three lines were constructed so that comparative tests could be made between the three types of amplifiers then available. One of these was fitted with amplifiers using van der Bijl’s type 101A tube. The vacuum tube emerged as a clear winner and van der Bijl always treasured the certificate confirming his membership in the Society of Planners and Builders of the First Transcontinental Telephone Line which was issued to each of the main participants.

By then, management was convinced that the vacuum tube held great promise, and van der Bijl was encouraged to develop and expand his knowledge of the triode. An immediate benefit came from a study of filament performance which revealed that the life could be improved considerably by increasing the electron-emitting area. The 101A tube had an inverted Vee filament drawing 1.45 A at 4 V. He replaced this with a double inverted Vee form which required 1.3 A at 5 V and increased the life from 400 h to 4500 h.

In September 1914, just after the start of World War I, van der Bijl designed a robust tube with coaxial cylindrical electrodes suitable for radio work which could be produced economically for military purposes. Fig. 11 includes the drawing of this tube which was prepared for U.S. Patent Application 1 738 269 (Dec. 1918) and which also appears in [7, p. 244]. Presumably, Western Electric ignored this design because it did not measure up to the needs of the telephone industry and failed to see the potential of the emerging military market. In three separate statements spread over almost 30 years, van der Bijl claims that this design forms the basis of the historical French Telegraphe Militaire (TM) tube. Several millions of these were made in France and the U.K. (where it was known as the valve).

In 1915, after successfully linking the country coast-to-coast by telephone, Western Electric turned its attention to transoceanic communication by experimenting with radio telephony. Speech had already been transmitted by radio but no method suitable for commercial use had thus far emerged. A team of engineers was assembled at Western Electric to explore the use of the vacuum tube for this purpose. Van der Bijl’s main contribution was the grid modulation system which was applied at a low level and amplified by up to 500 power tubes connected in parallel (the special power tubes for the transmitter were not designed by van der Bijl). The equipment was installed at the Navy Signaling station at Arlington, VA, so that it could take advantage of their large and efficient long-wave antennas. It succeeded in reaching Honolulu (7800 km) and Paris (6000 km) in 1915.

World War I

Toward the end of the war, van der Bijl was asked to develop a tube drawing the least possible filament power for use in battery-operated trench sets. The filament of the resulting VT-3 tube drew 0.2 A from a 2 V cell (0.4 W), which was about a tenth of the power required by previous tubes. The war ended before it could be put to military use, but van der Bijl continued with the development and produced the remarkably small tube known as the “peanut tube” using a simplified construction for which he was granted U.S. Patent 1 566 293. Western Electric made very few of these tubes but the design was licensed to several other manufacturers including Westinghouse and three in the United Kingdom where it was known as the Wecovalve.

The reduced filament power was greatly appreciated by the domestic radio market at a time when filaments were usually supplied by accumulators or dry cells.

Other Contributions

Van der Bijl worked on several other projects while he was in New York, including a speech inversion system which was eventually used to maintain secrecy on radio telephone circuits in the early 1930’s and a frequency division telegraph multiplexing system (U.S. Patent 1 502 889). He did some early investigations into facsimile transmission and introduced the use of photoelectric cells to register light-intensity variations in preference to the intended use of selenium cells.

There was a pressing need for a convenient cathode ray oscillograph to view high-speed electrical phenomena. The Braun tube had served this purpose quite well but it was heavy and cumbersome due to its high voltage power supply. Johnson of Western Electric had reduced the accelerating voltage considerably by replacing the cold cathode with an oxide-coated heated filament, but he ran into difficulties with focusing the electron beam. Van der Bijl suggested introducing a small amount of gas which became ionized by the electron beam and provided a surrounding field which reduced the scatter (U.S. Patent 1 565 873). Gas-focused cathode ray tubes were widely used in the 1920’s before the problem was solved using electron optics.

Van der Bijl gave expert witness in numerous patent disputes involving Western Electric. Notable among these was the Arnold versus Langmuir Interference 40 380, where testimony was also given by Richardson and Millikan. U.S. Patent Interference 45 928 against Chubb and his rectifier patent 1 657 223 asserted that van der Bijl had investigated smoothed half-wave and voltage doubler rectifier circuits as well as a DC to DC convertor using vacuum tubes as early as May 1914. In 1920, McGraw-Hill published his book The Thermionic Vacuum Tube and Its Applications. This summarized his work between 1913–1919 and became the standard textbook on the subject until well into the 1930’s with a total sale of about 10 000 copies. In 1924 McGraw-Hill suggested that the text should be brought up to date, but by that time van der Bijl had entered a new phase in his career and could not consider doing it himself. King, then Editor of the Bell System Technical Journal, was asked whether he would be willing to undertake the revision; he seems to have made a number of suggestions on how this should be done. Unfortunately, van der Bijl was not happy with the approach and the suggestions were never implemented. It is remarkable that a book on this rapidly developing subject written in 1920 should still have been selling as late as 1940.

Gen. Smuts, who served on the British War Cabinet from 1915–1918, was impressed by the scientific advice available to British ministers. He became Prime Minister of the Union of South Africa in 1919 and decided that his cabinet needed a Scientific Advisor. Having heard of van der Bijl’s achievements in America he decided that Hendrik was the man for the job. Van der Bijl was placed in a difficult position: on the one hand he was deeply entrenched at Western Electric doing work that he loved; on the other hand he had a deep roots in the country of his birth, which had enormous unrealized industrial potential and where he believed he could make an important contribution. In August 1920 van der Bijl’s colleagues at Western Electric bade him farewell with a whale of a party at which he was serenaded with a seven verse song to the tune of “The Gondoliers.” The words were set out, together with the signatures of 68 of his colleagues, on a large sheet of paper which van der Bijl had framed and which is now in the archives of the South African Institute of Electrical Engineers.

Return To South Africa

In 1920 van der Bijl returned to South Africa to take up the position of Scientific and Industrial Adviser to the department of Mines and Industries. He reported directly to Smuts, which gave him quite exceptional powers. Not surprisingly, the established civil servants did not take kindly to his position, and although he concluded several projects he was not at all happy with the situation and seriously considered returning to America.

A proposal to link the countries of the British Empire with a series of long-wave wireless telegraphy transmitters had been shelved at the beginning of World War I. Subsequently, a chain of radio stations, spaced 2000 miles apart, was being implemented when the Marconi Company lobbied for the system to be dropped in favor of their proposed direct links using short waves. By 1922 Australia had decided to back the new solution, but South Africa remained undecided. Van der Bijl was given the job of assessing the merits of the alternatives and favored the short-wave solution, which was eventually adapted by all the participating countries.

Clearly van der Bijl was still thinking about vacuum tubes and, stimulated perhaps by the forthcoming highpower short-wave radio links, he considered ways and means of making high-power tubes for radio transmitters. He believed that the solution lay in making the anode also serve as the tube enclosure, thus placing it in direct contact with the cooling medium. The problem lay with sealing the junction of the metal container and the glass structure supporting the remainder of the tube. Van der Bijl provided a platinum collar welded to the metal envelope at one end and fused to the glass at the other. It is possible to fuse glass to platinum without fear of fracture at higher temperatures because platinum has practically the same coefficient of expansion as glass. Unknown to van der Bijl, Houskeeper had been working along similar lines at Western Electric. Houskeeper’s seal relied on thinning the metal container where it was to be fused to the glass so that the internal stresses due to expansion were insufficient to cause cracking. Van der Bijl was granted a South African patent for his solution and applied for U.K. and U.S. patents. He had already negotiated royalties with the Marconi company to manufacture such tubes when they read, in the first issue of the Bell System Technical Journal, that Western Electric were already producing such tubes.

Smuts persuaded van der Bijl to form a national electricity supply undertaking and van der Bijl was made Chairman of the newly established Electricity Supply Commission in March 1923. This was a nonprofit public utility company which strengthened under his leadership and is today the main source of electrical power in South Africa. This seems to have settled his thinking because from then on, although the difficulties surrounding his enterprises did not diminish, his dedication to his vision of an industrialized South Africa became quite unshakeable.

Van der Bijl saw that the two pillars on which industry would be built were adequate and economical supplies of electric power and steel. A small steel-making business was already functioning but it was undercapitalized. At the time South African business was focused on the gold mining industry and there were few entrepreneurs with sufficient confidence in the future to invest in a steel business which was quite content to import its requirements. Van der Bijl persuaded the State to create a second public utility company to embark on this business on an adequate scale. Opposition was loud and persistent, but in 1925 he headed a new company known as the Iron and Steel Corporation (Iscor) which again prospered under his leadership and continues successfully to this day.

Van der Bijl saw the need to encourage smaller private enterprises, and in 1940 he persuaded the state to create the Industrial Development Corporation (IDC) to provide capital for promising enterprises. He was Chairman during its first three years of operation, and the IDC is still functioning today.

World War II

Once World War II started, South Africans began to realize just how dependent they were on imported goods, and with communications severely limited something had to be done urgently. Van der Bijl was made Director General of War Supplies and mobilized the country’s limited industrial resources in a remarkably short time. He arranged production facilities for guns, bombs, armored cars, precision instruments, military explosives and ammunition. Other existing industries such as weaving, clothing, leatherware, and canned foods were given a boost and developed rapidly so that the country could become independent of imported supplies.

As a Senior Civil Servant van der Bijl was remunerated quite adequately but could never accumulate the wealth a businessman of his stature would expect in private enterprise. He was more concerned about the quality of the products of a venture than with its potential profits and was convinced that the best vehicle for running a major undertaking was as a nonprofit making business with the state as sole shareholder. The Director General of War Supplies was expected to join the Cabinet but when Smuts invited van der Bijl to do so he declined.

After the war he directed expansion of the steel industry into a new industrial area known as Vanderbijl Park (near Vereeniging). A new ideal town was planned to house the workers complete with all facilities such as hospitals, schools, parks, etc., and in typical van der Bijl fashion this was achieved as perfectly as humanly possible. Here he floated the Vanderbijl Engineering Corporation (Vecor) to provide for the country’s heavy engineering needs. In association with U.S. interests he started the South African Marine Corporation to provide for shipping between South Africa and the United States. In 1943 he was elected Foreign Associate of the National Academy of Sciences of the United States and Fellow of the Royal Society in 1944. In 1945 he was Vice-President of the Institute of Radio Engineers. Van der Bijl died of cancer at the age of 60 in 1948.

Further Reading

The Remarkable Dr. Hendrik van der Bijl, by Dirk J. Vermeulen, originally published in Proceedings of the IEEE, Dec. 1998