American physicist (1852–1931)

Michelson, who was born at Strelno (now Strzelno in Poland), came to America with his parents when he was two years old. He graduated from the US Naval Academy in 1873 and remained there to teach physics and chemistry. Some five years later he began his work on measuring the speed of light and to this end he traveled to Europe to study optics at the Collège de France, Heidelberg, and Berlin. When he returned to America he left the navy to become professor of physics at the Case School, Cleveland. In 1882 he estimated the speed of light as 186,320 miles per second. This was the most accurate value then available and remained so for another ten years, when Michelson made an even more accurate measurement.

In the course of this work Michelson developed an interferometer, an instrument that can divide a beam of light in two, send the beams in different directions, and then unite them again. If the two beams traveled the same distance at different speeds (or different distances at the same speed) then, on being brought together again, the waves would be out of step and produce interference fringes on a screen. Michelson used the interferometer to test whether light travelng in the same direction as the Earth moves more slowly than light traveling at right angles to the Earth's surface. This was effectively testing the presence of the ‘ether’ – a substance that was supposed to exist in all space beyond the Earth's atmosphere. Because the ether was thought to be motionless and the Earth moved through it, it followed that light traveling in the same direction as the Earth would be more impeded than light going at right angles to it.

Michelson first conducted this experiment in 1881 in Berlin and got a negative result, that is there were no interference fringes and thus no evidence that the two beams were traveling at different speeds. He repeated the procedure several times under increasingly elaborate conditions until, in 1887, with Edward Morley (1838–1923), the experiment was made under near perfect conditions at the Case School. Again the ether could not be detected and physicists had seriously to consider that the ether did not exist. This result questioned much orthodox physical theory, and it remained for Einstein to develop the special theory of relativity to explain the constancy of the speed of light. Michelson was awarded the 1907 Nobel Prize in physics for this work.

Others, however, continued to report that they had found a measurable difference. Thus Dayton Miller (1866–1941), professor of physics at the Case School of Applied Science, Cleveland, Ohio took his equipment in 1925 to the 6000-ft summit of Mount Wilson in California. He claimed to have detected a difference of 6 miles per second for light travelling at right angles to the Earth's orbit. It was later established, however, that Miller's results were caused by different temperature conditions.

Michelson also applied interference techniques to astronomical measurements and was able to measure the diameters of various heavenly bodies by contrasting the light emitted from both sides. He also continued to make increasingly more accurate estimates of the speed of light and he suggested that the wavelength of light waves should be used as the length standard rather than the platinum–iridium meter in Paris. This suggestion was taken up in 1960 when light waves from the inert gas krypton became the standard measure.

The American physicist Albert Abraham Michelson (1852-1931) is important for his determination of the velocity of light and the study of optical interference.

Albert Michelson was born on Dec. 19, 1852, in German Poland. The family emigrated to the United States in 1854. He took the competitive examinations for congressional appointment to the U.S. Naval Academy. Although he qualified for the appointment, the place was awarded to another boy. Young Michelson traveled to Washington, was unsuccessful in getting President Grant to appoint him to the academy, but then persuaded the commandant to accept him.

Michelson graduated from the Naval Academy in 1873. Two years later he was appointed instructor in physics and chemistry there. He resigned his commission in 1880 and spent 2 years studying in Berlin, Heidelberg, and Paris. He was then appointed to the Case School of Applied Science at Cleveland, Ohio, as professor of physics. In 1889 he moved to Clark University as professor of physics, and in 1892 he was invited to head the department of physics at the new University of Chicago, a position which he held until 1931.

With few exceptions, all of Michelson's work bore directly on problems involved in the study of light; he was thus specialized to a degree that was unique among Americans at the end of the 19th century. While serving at Annapolis, he hit upon a slight but vital modification to a method then being used to measure the speed of light. With his simple device, consisting essentially of two plane mirrors, one fixed and one revolving at the rate of about 130 turns per second from which light was to be reflected, Michelson succeeded in obtaining a measure closer than any that had been obtained to the presently accepted figure - 186,508 miles per second.

Michelson performed his most famous experiment at Cleveland in collaboration with the chemist Edward W. Morley. Light waves were regarded as undulations of the ether which filled all space. If a light source were moving through the ether, the speed of the light would be different for each direction in which it was emitted. In the Michelson-Morley experiment two beams of light, sent out and reflected back at right angles to each other, took the same amount of time. Thus the notion of a stationary ether had to be discarded.

Even though his own work helped touch off a revolution in physics, Michelson never realized the fundamental nature of the change. Basically a brilliant experimenter, he saw the future development of physics only as one of further precision and newer instruments which would bring the accuracy of scientific measurements to the ultimate degree. He never understood the more mathematical and theoretical approach which came to dominate physics toward the end of his life.

Michelson's contributions were numerous. He developed, as a by-product of his interference experiments, the first spectroscope having sufficiently high resolution to disclose direct optical evidence of molecular motion; gave the scientific world a new fundamental standard of length when he calibrated the international meter in terms of wavelengths of cadmium; and, using a variation of his interferometer, became the first man to measure the diameter of a star. He received the Nobel Prize in 1907, the first American to be so honored. He died on May 9, 1931, while at work on a still more refined measurement of the velocity of light.

Further Reading

A good account of the major work of Michelson's life is in Bernard Jaffe, Michelson and the Speed of Light (1960). There is a useful biographical memoir of Michelson by Robert A. Millikan in National Academy of Sciences, Biographical Memoirs, vol. 19 (1938), and another profile of his life and work is in Royal Society of London, Obituary Notices of Fellows of the Royal Society, vol. 1 (1932-1935). The Nobel Foundation, Nobel Lectures: Physics, 1901-1921 (1964), has a biographical sketch.

For more information on Albert Abraham Michelson, visit Britannica.com.

(1852-1931), scientist. Although Albert Michelson was born in a Polish village to a Jewish father and a gentile mother, he became both a symbol and a star of American science as it stood in his time. He was three when his family immigrated to a California mining town, itself a symbol of American restlessness and hustle. Michelson graduated from the U.S. Naval Academy in 1873, ranking first among his classmates in optics. Unlike most Americans in the frenzied materialism of the Gilded Age, Michelson was attracted to science and found his métier in the sort of work most congenial to American scientists of his day: instrumentation and measurement. The ardent collection of discrete facts, rather than patient, long-range investigative projects, dominated American science in those years.

Michelson was a young physics instructor at Annapolis in 1877 when his department head urged him to open his lecture demonstrations with the French physicist Foucault's apparatus for measuring the speed of light. Michelson thereupon conceived an ingenious improvement on Foucault's device, simplifying it and significantly improving its accuracy. From then on, through almost half a century of university teaching, Michelson would pursue the holy grail of ultimate precision in measuring that fundamental physical constant. Early in the quest he confronted the problem of how light traveled. Scientists at the time generally accepted the theory that light traveled in the form of waves transmitted by a hypothetical substance they called the "ether," supposedly stationary and filling the entire universe. Michelson accepted that hypothesis and set out to determine the motion of the earth relative to the postulated ether.

In 1887, collaborating with a chemist friend, Edward W. Morley, Michelson carried out an ingenious experiment with a negative result: the speed of light was the same regardless of its direction relative to the earth's motion in space. The ether, if it existed, evidently had no effect, at least at the earth's surface. This startling finding did not, as legend has had it, directly inspire Einstein's theory of relativity (which ruled out ether), though it did lead others to ideas that in turn played a part in that theory, and it gave experimental support to the theory, once formulated. Michelson himself, weak in mathematics like most American physicists of the period, continued to believe in the ether and grudgingly accepted Einstein's theory only after many years, on the pragmatic grounds that it accounted for certain measurable phenomena.

Although he neither claimed nor craved a share in Einstein's glory, Michelson found consolation and pride in the instrument he had developed for the classic experiment: the interferometer. He refined and improved it brilliantly over the years, adapting it to a dazzling array of scientific measurements. It became one of the basic instruments of physical science, in a class with telescopes, microscopes, and thermometers. It was for his instruments and measurements, not for any contribution to relativity, that Michelson in 1907 became the first American to win a Nobel Prize in science. The honor was a sign of American science's coming of age. Ironically, that meant going beyond the very kind of science that Michelson had so famously represented.

Bibliography:

Dorothy M. Livingston, The Master of Light (1979); Loyd S. Swenson, Jr., The Ethereal Aether: A History of the Michelson-Morley-Miller Aether Drift Experiments, 1880-1930 (1972).

Author:

Robert V. Bruce

See also Science and Technology.

(mī'kəlsən) , 1852–1931, American physicist, b. Strelno, Prussia, grad. Annapolis, 1873, and studied at Berlin, Heidelberg, and Paris. He was professor of physics at Clark Univ. (1889–92) and later was head of the department of physics at the Univ. of Chicago (1892–1931). He is known especially for his determinations of the speed of light; in some of his earliest work he tested the data of Foucault's experiments and, then and later, with apparatus (including the interferometer) that he designed and built himself, measured the speed of light to an unequaled degree of accuracy. He measured (1892–93) the length of the standard meter in Paris in terms of the wave length of the red line of the cadmium spectrum, using his interferometer method. The wave length thus provided an absolute and exactly reproducible standard of length. With E. W. Morley he conducted the Michelson-Morley experiment (1887), which failed to detect any difference in the speed of light caused by the motion of the earth through space. That led to the refutation of the ether hypothesis and contributed to the development of Einstein's theory of relativity. Michelson was the first to measure the diameter of a distant star. He also demonstrated that the earth as a whole is rigid, not molten. Awarded the 1907 Nobel Prize in Physics, he was the first American scientist to receive the honor. His major writings include Velocity of Light (1902) and Studies in Optics (1927).

Bibliography

See biography by his daughter, D. M. Livingston (1973).

This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)