Collaboration: The Photoelectric Photometer

The photoelectric photometer was a great invention that improved the the field of astronomy by leaps and bounds. It started when Joel Stebbins’s wife (May) decided she wanted him home earlier, so she suggested Stebbins make use of electricity. As Stebbins searched for a better method recording star magnitudes, he met and became friends with F.C Brown. Brown was a physicist, who, at a demonstration, used a lamp to illuminate a selenium cell. When the lamp was on, a bell would ring. Turn it off, and the bell would stop.  Brown and Stebbins continued to work together to make an improved selenium cell.

After Brown left to pursue a fellowship at Princeton, Stebbins met Jakob Kunz, a colleague also working at Illinois. Kunz was developing his own photoelectric cell, and the collaboration of the two would result in Kunz’s photoelectric cells being put inside Stebbins’s photometer. From 1913 until his death, Kunz would provide Stebbins with ever new and improved photoelectric cells. According to Stebbins, these cells were far better than any other procurable at the time. Kunz’s cells provided greater sensitivity and faster operation to the selenium ones Stebbins was using.

This collaboration resulted in the measurement of many previously unrecorded stars, as well as several increases in photoelectric technology. 

Joel Stebbins with his invention: the Photoelectric Photometer, circa 1925

Department portrait of Jakob Kunz, signed by him, University of Illinois,  date unknown. 

Click Below to find out more about who was involved:

Joel Stebbins

Jakob Kunz

F.C. Brown

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Joel Stebbins

Stebbins was born in Nebraska in 1878 and graduated from the University of Nebraska in 1899. After completing his graduate work at the Washburn Observatory in Madison Wisconsin, he moved on to the Lick Observatory. There, in 1903, he became the third man to earn his doctorate in astronomy from the University of California and Lick Observatory where he is still considered one of the greatest researchers produced by Lick.Though originally at Mount Hamilton and Berkeley, Dr. Joel Stebbins decided that the University of Illinois provided with more opportunity, so in 1903 he accepted directorship of the Observatory.

Joel Stebbins with his invention: the Photoelectric Photometer, circa 1925

His early administration was marked with many changes: the Observatory was integrated in the Mathematics Department as the Division of Astronomy and had no operating budget. After spending eight dollars out of his own pocket, Stebbins convinced the Board of Trustees to create the first budget for the Observatory: $750. In addition, the curriculum was expanded from three classes to nine classes, including Astronomy for Engineers, Observational Astronomy, Seminar and Thesis. Most of the classes, taught by Stebbins and an instructor, required weekly use of the Observatory's facilitates.

Early on, Stebbins used the popular Pickering visual program to survey stars in search of undetected eclipsing binary stars. Later in 1904, he began the estimates of the relative magnitudes of 107 double stars, duplicating the work of astronomer E.C. Pickering in 1878.It was during Stebbins' photometric project when he first realized the need for a new method of photometry. In the summer of 1905, Stebbins was married and he soon found a source of inspiration for a new photometer. He provided the following account at a dinner of the American Astronomical Society in 1957:

“The photometric program went along well enough for a couple of years until we got a bride in our household, and then things began to happen. Not enjoying home alone, she (May Stebbins) found that if she came to the observatory and acted as recorder, she could get me home earlier. She wrote down the numbers as the observer called them, but after some nights of recording a hundred readings to get just one magnitude, she said it was pretty slow business. I responded that someday we would do this by electricity. That was a fatal remark. Thereafter she would often prod me with the question: "When are you going to change to electricity?" It happened that within a two or three months the department of physics gave an open house, and one of the exhibits was in charge of a young instructor F.C. Brown. He showed how when he turned on a lamp to illuminate a selenium cell, a bell would ring; when the lamp was off, the bell would stop. Here was the idea; why not turn a star on to a cell on a telescope and measure the current?” (Stebbins, Early Photometry, 507)

This friendship with F.C Brown soon led to the development of  a selenium cell photometer, which ultimately led to the discovery of  five new eclipsing binary stars, constructed a light curve for the Moon, determined the mid-eclipse time of the 24 July, 1907 lunar eclipse and determined the magnitude of Comet Halley in May, 1910. However, Stebbins was not happy with the photometer. The cells were not very sensitive, only stars brighter than the third magnitude could be studied. They also had a narrow spectral response, were not readily available, were difficult to work with and the characteristics varied from one cell to another. The solution to Stebbins' problems was found in physicist Jakob Kunz.

Kunz, in partnership with Stebbins, developed and installed a photoemissive photocell instead of a selenium based one. This worked fabulously. Kunz and Stebbins remained friends and continued to develop better cells for the photometer. Using the photometer, they even succeeded in measuring the brightness of the solar corona from the eclipse on 9 June, 1918.

Professor Stebbins left Illinois in September 1922 when he was offered the directorship of Washburn Observatory. Stebbins continued to improve and apply the photometer there where he enlisted the help of A. Whitford who developed a thermonic amplifier, C. M. Huffer, an Illinois math graduate who had taken a class with Stebbins at Illinois, and G. Kron at Mt. Hamilton who worked with photomultiplier tubes. Stebbins remained at the forefront of astronomical photometry until his death in 1966.

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Works Cited:

Joel Stebbins Papers, courtesy of the University of Illinois Archives Series No. 15/3/21, Box 1.

Stebbins, Joel. (1910)The Measurement of the Light of Stars with a Selenium Photometer. With An Application to the Variations of ALGOL. The Astrophysical Journal, Vol. 32 (3)

The Color Sensibility of Selenium Cells. The Astrophysical Journal. University of Chicago Press. 27(3). April 1908. 

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Jakob Kunz

Jakob Kunz was born in Brittnau, Switzerland, on November 3rd, 1874. He was educated in the public schools there until he attended Zurich Polytechnikum, where he gained both his B.S. and Ph.D.

Department portrait of Jakob Kunz, signed by him, University of Illinois,  date unknown.

After serving in various universities and laboratories abroad, Kunz came to United States in 1908. He worked at the University of Michigan for one year before being offered the role of assistant professor of mathematical physics at the University of Illinois, where he remained for the rest of his life, working up through associate professor to professor.

For years Kunz was practically solely responsible for the whole of graduate courses in mathematical physics. However, he never taught undergraduate courses, with friends noting that he probably did not like the “immature and almost passive attitude” of American undergraduate students.

Kunz was renown for his clear and thorough lectures on classical theoretical physics, but he never reconciled to more “modern” notions as could be found in relativity and quantum mechanics. Indeed, a colleague noted “as he was himself thoroughly familiar with the mathematical structure of these theories, his objections and criticisms were occasionally very penetrating; and indeed troublesome to any who had a tendency to accept them on faith or authority”.
However, Kunz is most famous for his work with photoelectric cells. Photoelectric cells are devices whose electrical characteristics (voltage, etc) vary when subjected to light. Being among the first to work with them in the country, he developed a specially sensitized alkali photoelectric cell. This cell, free from dark current, was far superior for certain astronomical purposes than anything else available at the time. An example of such astronomical purposes was studying the intensity of the sun’s corona during an eclipse.
Kunz was enthusiastic about many subjects, and often attended seminars conducted in the fields of chemistry, mathematics, and engineering. Though often in poor health during the last part of his life, he maintained an active presence in both teaching and research up until a few weeks before his death on July 18th, 1938.
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Works Cited:

Loomis, F.W. (1938). “Jakob Kunz”. Obituary Draft. Found in University Archives Series No. 11/10/ 25, Box 2.

“Portrait of Jakob Kunz” (Unknown). Found in University Archives Series No. 11/10/ 25, Box 2.