Albert Abraham Michelson
Albert Abraham Michelson (1852-1931)
1931 Obituary[1]
"THE LATE PROF. A. A. MICHELSON, F.R.S.
By the death of Professor Michelson, at Pasadena, last Saturday, the world has lost a prince of experimentalists. Born at Strelno, Prussia, in 1852, Michelson was, whilst still an infant, taken by his parents to San Francisco, His early education was received in the public schools, from which he passed to the U.S. Naval Academy, graduating in 1873. His record was such that in 1875 he was appointed instructor there in physics and chemistry, and it was when holding this position that he carried through the earlier of those experiments on light which secured for him an international reputation. These were directed to a measurement of its velocity in vacuo.
The figure found by him in 1879, using a modification of the Foucault method, was 2-999 x 10w cm. per second. In further experiments, made in 1882, this figure was reduced to 2-9985 X 1OIU.. The problem never lost interest for him, and by Successive small improvements in his methods and apparatus, the true figure has been determined with such precision that the distance between primary triangulation stations can, it has been claimed, be measured more accurately by noting the time taken for light to traverse it than by orthodox surveying methods. Resigning his position at the Naval Academy in 1879, Michelson was for some time employed in the Nautical Almanac Office at Washington, and he later studied at Berlin, Heidelberg and at Paris.
In 1883, he was appointed Professor of Physics at the Case School of Applied Science, Cleveland, and here it was that the epoch-marking Michelson-Morley experiment was carried out. The phenomenon of aberration discovered by Bradley, in 1727, had led to the belief that the ether streamed through solid bodies “like the wind through a grove of trees,” and the experiment in question was designed to measure the relative velocity of the earth to the ether.
A null result was obtained and this ultimately led to Einstein’s theory of relativity, based primarily on the postulate that if such a relative velocity exists, it can never be detected experimentally. It may be true, as Sir A. Eddington contends, that the discovery of the nuclear structure of the atom is of a still more revolutionary character, but whilst everybody had fairly definite ideas as to the nature of time and space, few knew anything about atoms, so that the ultimate outcome of the Michelson-Morley experiment has appeared correspondingly more striking to the popular imagination. By his invention of his interferometer, Michelson established a new standard of precision in measurements of length. Working in conjunction with Benoit, in 1894, he found that the wavelength of a certain red line in the cadmium spectrum was 6438-4700 X 10*10 m.
A subsequent redetermination by Benoit, Fabry and Perot, in 1907, gave the value 6438-4702. Michelson was also the first to prove experimentally the truth of Rayleigh’s suggestion that .the width of spectral lines was due to a Doppler effect, since the radiations are received from molecules or atoms moving at widely different velocities. He experimented also on tidal effects on the solid earth, using underground pipes of such a length that by his delicate methods of measurement, differences, due to the lunar attraction, could be observed in the water level at opposite ends of the pipe. His results are considered the most accurate determinations of this kind yet made. Another striking achievement to Michelson’s credit is the direct measurement of the diameter of certain of the fixed stars. This was effected at Mount Wilson by a modification of his interferometer. In even the largest telescopes or, indeed, most markedly in the largest, the image of a fixed star appears to be a mere point of light. By the interferometer, however, interference effects were obtained of rays proceeding from opposite sides of the star. The results showed, as had been previously estimated by indirect methods, that the diameter of Betelgluse was large enough to include within the star, the whole of the earth’s orbit; the diameter found being 260,000 miles. In 1889, Michelson became Professor of Physics at the Clark University and three years later was appointed to the corresponding chair at Chicago.
He was awarded the Nobel prize for Physics in 1907, and the Copley Medal of the Royal Society in the same year. He was also a gold medallist of the Royal Astronomical Society."