Experimental Determination of the Velocity of Light (Classic Reprint)
(Excerpt from Experimental Determination of the Velocity o...)
Excerpt from Experimental Determination of the Velocity of Light
In November, 1877, a modification of Foucault's arrangement suggested itself, by which this result could be accomplished. Between this time and March of the following year a number of preliminary experiments were performed in order to familiarize myself with the optical arrangements The first experiment tried with the revolving mirror produced a deflection considerably greater than that obtained by Foucault. Thus far the only apparatus used was such as could be adapted from the apparatus in the laboratory of the Naval Academy.
At the expense of $10 a revolving mirror was made, which could execute 128 turns per second. The apparatus was installed in May, 1878, at the laboratory. The distance used was 500 feet, and the deflection was about twenty times that obtained by Foucault.* These experiments, made with very crude apparatus and under great difficulties, gave the following table of results for the velocity of light in miles per second.
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Albert Abraham Michelson was born on December 19, 1852, at Strelno, a small Prussian town near the frontier of Poland. His parents, Samuel and Rosalie (Przlubska) Michelson, came to America in 1854. After a short stay in New York the family went by boat via Panama to San Francisco; thence the gold rush took them first to Murphy's camp in Calaveras County, California, and later to Virginia City, Nevada, close to the bonanza silver mines.
Education
Michelson received his early schooling at Virginia City and, when his parents returned to San Francisco, completed his primary and secondary education in the schools of that city. Because of his evident interest and talent in science, his high-school teachers urged him to continue his education. He took the competitive examinations for congressional appointment to the United States Naval Academy, resulting in a tie between himself and another boy. He graduated from the Naval Academy in 1873.
His career was rather unique in that, although he never received an academic degree in recognition of the completion of any course of study, he was the recipient of eleven honorary degrees from American and European universities.
Career
Through political influence, Michelson got the appointment. On the suggestion of the examining committee, Michelson then decided to try for one of the ten appointments at large, and, although only seventeen, set out for Washington to interview President Grant. He was successful in obtaining the interview but unsuccessful in getting one of the appointments available. On the eve of Michelson's departure from Annapolis again to interview the President, the Commandant, in recognition of his ability and tenacity of purpose, made a place for him as an eleventh appointment. After the usual period of required service, he was appointed instructor in physics and chemistry there (1875 - 79). This service was followed by study in the University of Berlin in 1880, at Heidelberg the following year, and in Paris at the Collège de France and the École Polytechnique in 1882. Called to the Case School of Applied Science as professor of physics in 1883, he held this position until 1889. Thence, he went to Clark University as professor of physics (1889 - 92). With the organization of the new University of Chicago in 1892, he was called by President Harper to be head of the department of physics, and this position he held until retirement to emeritus professor in 1931. He was made a "distinguished service" professor of physics at Chicago in 1925. He was Lowell lecturer in 1899, his lectures were later published under the title, Light Waves and Their Uses (1903); served on the Bureau International des Poids et Mesures, 1892-93; and on the International Committee of Weights and Measures in 1897. He was an exchange professor at the University of Göttingen in 1911. In American Men of Science Michelson's official field is succinctly summarized in one word, "Light. " His entire scientific career, begun while a student at Annapolis and continued without pause until in his seventy-ninth year he suffered a cerebral hemorrhage that caused his death at Pasadena, California, on May 9, 1931, is summed up in some seventy-nine published papers. The first of these, printed in The American Journal of Science (May 1878), when he was twenty-six years of age, bears the title, "On a Method of Measuring the Velocity of Light"; the last, written shortly before he lost consciousness, but as yet unpublished, is on the same subject. In some aspect or other, the light was the topic of all but twelve of these papers. His work in this field can be divided into two main categories, the first being the problem of the accurate determination of the velocity of light, and the second the study of optical interference. With respect to his work on the velocity of light, neither the young man of twenty-six nor the old man of seventy-nine ever had a rival.
Michelson's work on the interference of light was also begun rather early in life, the first paper being published in The American Journal of Science in August 1881, under the title, "The Relative Motion of the Earth and the Luminiferous Ether. " This title explains the fundamental object of all of this work, which was to detect, if possible, the absolute motion of the earth as, trailing along with the rest of the solar family, it follows the sun's plunging course through space.
In his first experiments, carried on at the Naval Academy, Michelson conceived the idea of slightly modifying the optical path of an apparatus which had been used earlier by Léon Foucault. Foucault's unmodified experiment was at that time being carried on under the leadership of Prof. Simon Newcomb, of the Naval Academy, on a very elaborate scale supported by thousands of dollars of the congressional appropriation. Michelson, by changing the position of one mirror, was able, with equipment designed and built by himself and costing less than ten dollars, to achieve precision equal to or superior to that of the official apparatus. This was the first instance of his ingenuity with respect to physical phenomena. In his last determination of the velocity of light, which embodies many refinements of his original plan, an accuracy of about three parts in a million is expected, which means that the journey of more than one hundred and eighty-six thousand miles made by light in one second will be known to within half a mile.
In common with his distinguished predecessors and his contemporaries, Michelson held the idea that light consists of an electromagnetic wave motion carried through a luminiferous ether, with respect to which, as a fixed system of reference, cosmical motions might be measured. It is well known now that these experiments and all others which have been designed to determine absolute motion have given completely negative results. It is equally striking testimony to confidence in his work that Michelson's first disclosure of the abortive character of this experiment was accepted without question by experimental and theoretical physicists the world over, and that a new philosophy with respect to the fundamentals of physical science was immediately attempted. This new philosophy reached its highest development in the hands of Einstein, first as the special theory of relativity, and later as the general relativity theory. Only within comparatively recent years when a somewhat more modern design of apparatus and many thousands of observations by another worker appeared to give a minute residual effect, was the experimental problem subjected to another rather widespread attack, not only by Michelson himself but by other experimenters in America and Europe. The upshot of these latest experiments has been a complete confirmation of Michelson's earlier assertion. The constancy of the velocity of light, irrespective of the motion of either source or observer, is perhaps the keystone of the structure of modern physical theory.
In collaboration with Thomas Chrowder Chamberlin and one or two other colleagues, Michelson applied the delicate methods of measurement by means of interference to the problem of the rigidity of the earth, using for this purpose the ebb and flow of such tiny tides as are engendered in a six-inch iron pipe five hundred feet long, filled with water and buried underground. This investigation confirmed early provisional estimates by Kelvin, based on celestial mechanics, that the earth possessed a rigidity of the same order of magnitude as that of steel. These experiments showed in addition that the earth's viscosity also was not much different from that of steel.
Quotations:
“The more important fundamental laws and facts of physical science have all been discovered, and these are now so firmly established that the possibility of their ever being supplanted in consequence of new discoveries is exceedingly remote. Nevertheless, it has been found that there are apparent exceptions to most of these laws, and this is particularly true when the observations are pushed to a limit, i. e. , whenever the circumstances of experiment are such that extreme cases can be examined. Such examination almost surely leads, not to the overthrow of the law, but to the discovery of other facts and laws whose action produces the apparent exceptions. As instances of such discoveries, which are in most cases due to the increasing order of accuracy made possible by improvements in measuring instruments, may be mentioned: first, the departure of actual gases from the simple laws of the so-called perfect gas, one of the practical results being the liquefaction of air and all known gases; second, the discovery of the velocity of light by astronomical means, depending on the accuracy of telescopes and of astronomical clocks; third, the determination of distances of stars and the orbits of double stars, which depend on measurements of the order of accuracy of one-tenth of a second-an angle which may be represented as that which a pin's head subtends at a distance of a mile. But perhaps the most striking of such instances are the discovery of a new planet or observations of the small irregularities noticed by Leverrier in the motions of the planet Uranus, and the more recent brilliant discovery by Lord Rayleigh of a new element in the atmosphere through the minute but unexplained anomalies found in weighing a given volume of nitrogen. Many other instances might be cited, but these will suffice to justify the statement that 'our future discoveries must be looked for in the sixth place of decimals. ”
“The generalized theory of relativity has furnished still more remarkable results. This considers not only uniform but also accelerated motion. In particular, it is based on the impossibility of distinguishing an acceleration from the gravitation or other force which produces it. Three consequences of the theory may be mentioned of which two have been confirmed while the third is still on trial: (1) It gives a correct explanation of the residual motion of forty-three seconds of arc per century of the perihelion of Mercury. (2) It predicts the deviation which a ray of light from a star should experience on passing near a large gravitating body, the sun, namely, 1". 7. On Newton's corpuscular theory this should be only half as great. As a result of the measurements of the photographs of the eclipse of 1921 the number found was much nearer to the prediction of Einstein, and was inversely proportional to the distance from the center of the sun, in further confirmation of the theory. (3) The theory predicts a displacement of the solar spectral lines, and it seems that this prediction is also verified. ”
“The velocity of light is one of the most important of the fundamental constants of Nature. Its measurement by Foucault and Fizeau gave as the result a speed greater in air than in water, thus deciding in favor of the undulatory and against the corpuscular theory. Again, the comparison of the electrostatic and the electromagnetic units gives as an experimental result a value remarkably close to the velocity of light–a result which justified Maxwell in concluding that light is the propagation of an electromagnetic disturbance. Finally, the principle of relativity gives the velocity of light a still greater importance, since one of its fundamental postulates is the constancy of this velocity under all possible conditions. ”
Membership
fellow of the Physical Society of London, foreign member of the Royal Society of London, honorary fellow of the Royal Society of Edinburgh, corresponding member of the British Association for the Advancement of Science, fellow of the Royal Astronomical Society, honorary member of the Royal Institution of Great Britain, honorary member of the Royal Irish Academy, foreign associate of the Académie Française, foreign associate of the Académie des Sciences (Paris), honorary fellow of the Optical Society of America, a foreign member of the Reale Accademia dei Lincei (Rome), member the American Astronomical Society, the American Academy, the Société Française de Physique, the Société Hollandaise des Sciences, the Deutschen Physicalische Gesellschaft, the Kungliga, Fysiografiska Sällskapet, Lund, and the Russian Academy of Sciences
Personality
No account of this great figure is complete without some reference to a few aspects of his personality, other than scientific. Albert's life was a magnificent exhibition of singleness of purpose, unruffled by winds of favor or disfavor. Even the cosmic forces of love, hate, jealousy, envy, and ambition seemed to move him little. Possessed of an astonishing indifference to people in general because of his absorption in his scientific pursuits, he nevertheless had the capacity of making and cherishing a few devoted friends. As a teacher, his lectures were models of acute organization and clarity of exposition. Comparatively few students in his classes aroused his personal interest, but those who did found no end of patience and sympathetic and intelligent consideration for their scientific or their personal problems. As the executive head of a large and important department in a great university, it was his practice to delegate full responsibility with respect to all details to others.
However, whenever his colleagues or his staff needed his support, no one was ever more quick to champion their cause as his own. In such situations, his clarity of vision, fearlessness, and swift assumption of initiative usually won the desired results with little effective opposition. Michelson's primitive simplicity of character showed itself in his intuitions with respect to natural phenomena and in the boldness and the brilliance of his attack upon those citadels wherein nature keeps her most carefully treasured secrets. His inquiries were of highly fundamental character. The man's artistic side might have been regarded as exhibiting versatility. He was a musician of some talent on the violin, and the musical instructor of some of his children; in water color and in oil he was an artist of unusual skill and feeling, for an amateur. All who knew him well realized that the feeling of the artist was the keynote of his scientific work as well.
On one occasion in Chicago, he had been prevailed upon to exhibit some of his water colors in one of the university halls. Physical force had been almost necessary to get him there in person. A lady came up to him and said that she felt he must have made a great mistake when he abandoned art for science. Michelson, with that characteristic grave courtesy that he always achieved when disagreeing with another's opinion, replied that he hoped she was mistaken; to his own way of thinking, he said, he felt he had never abandoned art. He said it was his conviction that in science alone was art able to find its highest expression.
Quotes from others about the person
F. R. Moulton, in an appreciation of Michelson published in Popular Astronomy (June-July 1931), admirably expresses the spirit of his work: "He was unhurried and unfruitful. He was never rushed by University duties; he never drove himself to complete a laborious task; he never feared that science, the University, or mankind was at a critical turning point; he never trembled on the brink of a great discovery. If I have correctly caught the dominant note of his life, Michelson was moved only by the 'esthetic enjoyment his work gave him. In everything he did, whether it was work or play, he was an artist. He pursued his modest serene way along the frontiers of science, entering new pathways and ascending to unattained heights as leisurely and as easily as though he were taking an evening stroll. "
Connections
On April 10, 1877, Michelson was married to Margaret McLean Heminway, from whom he was later divorced. By this marriage there were two sons and a daughter; one son predeceased him. On December 23, 1899, he was married to Edna Stanton of Lake Forest, Illinois, who bore him three daughters.