A FEW years ago when the Naval Institute established the policy of publishing each month a photograph of a distinguished graduate of the U. S. Naval Academy in civil life, the series was headed by a picture of Professor A. A. Michelson of the class of 1873. Because of Professor Michelson’s remarkable career and singular achievements, which have contributed in no small way toward inspiring a new trend of thought in the realm of modern physics, it is perhaps not out of order to augment the recognition already rendered our distinguished fellow alumnus by a somewhat more detailed account of his professional career.
In a recent issue of the New York Times[1] an item is headlined “Michelson, at Seventy- six, Outlines Three New Tasks.” From this, one may conclude, and rightly, that at present Professor Michelson is actively engaged in his researches; and accordingly, it would be folly were I to endeavor here to appraise his contributions or extol his works at a time when they are still in the process of being refined and perfected.
It is my purpose merely to sketch briefly the scientific achievements of the man whose first researches were carried out at the U. S. Naval Academy over fifty years ago and who now, at the age of seventy-six, has set for himself three tasks which to others, even in his own field, seem almost Herculean. And furthermore, it will be interesting to note the far-reaching significance and influence on contemporary thought in physics that may be attributed to these major researches of Professor Michelson.
More than three-quarters of a century have passed since Albert Abraham Michelson was born in a small village, Strelno, just forty miles from the birthplace of Copernicus and then, 1852, a part of Germany, but now within the borders of Poland. But during practically all of that time he has lived in America as a citizen of the United States.
At the age of sixteen he was appointed by President Grant as a midshipman at the U. S. Naval Academy and was graduated four years later in the class of 1873, or as then designated, “Date of ’69.” One reads with interest Admiral Fiske’s account[2] of his boxing tilt with Michelson when they were schoolmates at the Naval Academy, a fight from which Fiske emerged in rather the worse condition. However, upon the admiral’s own admission, his admiration of Michelson the “pugilist” is surpassed by his admiration of Michelson the physicist. We also learn from Admiral Fiske that an innate interest in physical experiment and evidence of unusual ingenuity were observed in Michelson during his years as midshipman; although Admiral Worden,[3] so it is alleged, was a bit concerned for the future of one who devoted so much of his time to extracurricular experiments. Humanity may be thankful for the influence that then permitted the individual to follow his true bent undeviated by the rigid restraints of a military regime.
Not very long after graduating Michelson was detailed to the Naval Academy (1875- 1879) as an instructor in mathematics and physics, and at that time he outlined in a simple, characteristic half page in Nature[4] an improved method of determining the velocity of light.
Before the Navy had established a postgraduate school, certain officers were selected and sent abroad for graduate study, and in this line of duty Michelson spent the years 1880 to 1882 in Berlin, Heidelberg, and Paris; and in the following year he resigned from the Navy to enter upon an academic career. It is interesting to note that thirty-six years later (1918) he was again on the Navy Register, enrolled in the U. S. Naval Reserve Force as a specialist. I recall with pleasure making a visit during the War to the roof of his laboratory at the University of Chicago where he was developing an optical range finder for use by Navy vessels.
Following his early Navy career, Michelson became a professor of physics first at the Case School of Applied Science at Cleveland and later at Clark University at Worcester and finally, since 1892, at the University of Chicago, to which he was called as head of the Department of Physics.
The recognition of Professor Michelson as a scholar and an investigator of the highest order is borne out by the many honors, both foreign and domestic, of which he has been the recipient. His awards, such as the Rumford Medal, the Copley Medal, etc., are too numerous to mention here, but one cannot resist pointing particularly to the fact that Professor Michelson was the first American physicist to receive the Nobel Prize Award.
Although for nearly forty years Professor Michelson has made his home in Chicago, much of his time has been recently spent in California where, even during the last summer, he has been repeating the ether-drift and velocity-of-light experiments, always with new and improved technique, increased precision, and with convincing results. It is thus that we learn of “Michelson, at Seventy-six, Outlines Three New Tasks” which are in brief: the redetermination of the velocity of light; a refinement of the measurement of the diameters of stars; and another search for a possible ether-drift.
It may be of interest now to review very briefly the principle researches of Professor Michelson; and then to consider their bearing and influence on current physical thought.
Probably the first serious effort to find out whether or not the velocity of light is finite was made by Galileo; but the crudeness of his experiments left him with no evidence that the passage of light from one point to another was not instantaneous. In 1676 the Danish astronomer, Romer, pointed out that inequalities of the time intervals between eclipses of Jupiter by one of its satellites may be accounted for by the varying distance of the earth from that planet due to the periodic motion of the earth about the sun and at the same time assuming a finite velocity of light of about 192,000 miles per second. Subsequently, short-range determinations of this velocity were made, and noteworthy were the toothed-wheel experiments of Fizeau (1849) and Cornu (1874), and at the same time the revolving-mirror experiment of Foucault.
The method of determination of the velocity of light as proposed by Michelson4 in 1878 was that of the revolving mirror, driven by an air blast and calibrated against a tuning fork of accurately known frequency. The apparatus for this experiment was set up along the sea wall of the Naval Academy at Annapolis, a position which is now occupied by the tennis courts. Here an unobstructed path of five hundred feet between mirrors was obtainable. The results of this experiment were published in the Proceedings of the American Association for Advancement of Science5 in 1878, and the best value obtained, 186,508 miles per second, was a mean of ten independent observations "made under difficulties, and with apparatus adapted from material found in the laboratory of the Naval School.”
In the years subsequent to 1878 improvements in the measurements of the two fundamental factors in this experiment, the distance interval and the time interval of the passage of the light beam, have been made under the direction of Professor Michelson. The distance between mirrors in the 1924 determination6 was about twenty-two miles, accurately measured for the purpose by the U. S. Coast and Geodetic Survey, between Mount Wilson and Mount San Antonio in California. The rotating mirror in this case was in the form of an octagonal prism, each face being an optical flat, and it functioned also as a timer by virtue of its calibration with a standardized tuning fork. This experiment has given what is by all odds the most trustworthy value of the velocity of light, namely, 186,359 miles per second in air.
In the early eighties, when in Germany, Professor Michelson’s interests were first directed to the "Aberration Question,” which in short was this: “Does the medium, usually called ‘ether,’ in which light waves are propagated through empty space, remain fixed with respect to the stellar universe while the earth moves freely through it; or does the earth drag the ether with it, as a rapidly moving vehicle carries a quantity of air with it into its motion?”
A study of this question, both experimental and theoretical, has led the way to a vastly greater comprehension of the universe in which we live than has, perhaps, ever been realized before. In particular, the results of the now famous “Michelson and Morley Ether-Drift Experiment,” carried out at Cleveland in 1887, gave the initial impetus to the theory of relativity. Let us pause for a moment to consider this far-reaching experiment.
As early as 1880, Professor Michelson conceived the idea of making a direct test for ether-drift by sending simultaneously two beams of light waves out from a point in two mutually perpendicular directions, and by means of mirrors reflecting each back along its own path to the starting point. If, during such an experiment, there is no drift of the ether, the two beams of light waves will arrive together in step; but, on the other hand, if there is a drift of the ether along the path of one of the light beams, then the two sets of waves will arrive somewhat out of step. To measure such a possible “out-of-stepness” Michelson invented (1882) a simple but tremendously ingenious interferometer, an instrument which has since found application in many and various types of optical measurements.
His first effort to detect ether-drift with an interferometer was in Helmholtz’ laboratory in Berlin; but here the vibrations due to city traffic made the use of this instrument impossible, and accordingly the apparatus was moved to Potsdam. The results obtained there, however, were considered inaccurate and therefore of no significance.
Upon returning to America, Professor Michelson, assisted by Professor Morley, built an interferometer on a large scale at the Case School of Applied Science; and there they made the surprising observation that the light waves reflected back along the two perpendicular paths of the interferometer met one another “in step.” The immediate interpretation of this was that there was no relative motion, that is, no drift, between the earth and the ether. This experimental observation was repeated later, and with increased precision, by Morley and Miller at Cleveland, and by Michelson at the University of Chicago, and in each instance the original Michelson-Morley experiment was substantiated.
This experimental result which indicated no ether-drift was in contradiction to the supposed facts deduced from observations of aberration; and as late as 1900 Lord Kelvin, at the International Congress of Physics held in Paris, averred that the “only cloud in the clear sky of the theory of the ether was the null result of the Michelson-Morley experiment.” But at about that time Lorentz, in Holland, and Fitzgerald, in Ireland, proposed an hypothesis to make compatible the results of the Michelson-Morley experiment and the earlier aberration experiments ; and it was this hypothesis, now usually referred to as the Lorentz-Fitzgerald contraction hypothesis, on which Einstein founded his theory of relativity in 1905. The influences of this theory are too numerous and too profound to mention here, but suffice it to say that they have introduced entirely new and extremely interesting speculations as to the structure of atoms and in general the nature of things.
In the years 1921 to 1925 very extensive ether-drift experiments were carried out by Professor Miller at the Mount Wilson Observatory in California. Physicists the world over were astounded when Professor Miller announced an observed motion of the ether of about ten kilometers per second; for such a result was apparently in disagreement with the Michelson-Morley experiment and with the theory of relativity. Professor Miller then carefully repeated the experiment and verified this former result, but the same experiment was done independently at Mount Wilson by Dr. Roy Kennedy, who found no evidence of an ether- drift. A few years later Professor Michelson went to California and there repeated his ether-drift experiment, and in November of 1928 at Washington he announced to a very eager and attentive audience at a meeting of the Optical Society of America the result of this last and most precise experiment—no observable ether-drift. The contrary results of Professor Miller’s experiments, done under his keen supervision and skillful hand, still stand unexplained; but the situation, as recognized by the scientific world, is that relativity remains vindicated.
In conclusion I wish to speak briefly of some of the other important achievements of Professor Michelson. I have mentioned the interferometer which was devised by him for the purpose of determining a possible ether-drift. This same instrument has found most remarkable applications in other fields of science, notably in the measurement of the distance between components of double stars or in the measurement of the diameter of the giant star Betelgeuse. In this latter instance an interferometer was mounted on the end of the 100-inch reflecting telescope at the Mount Wilson Observatory; and the diameter of this great star, located in the constellation of Orion, was calculated to be 240 million miles, a distance about equal to the diameter of the orbit of Mars.
The international standard of length is the distance between two scratches on a particular bar of platinum-iridium kept at Sevres near Paris, and is known as the standard meter. In order to establish permanently this standard of length so that it might never be lost to mankind due to material destruction, Professor Michelson spent the first year of his appointment at the University of Chicago in Paris in determining this length in terms of the wave length of a particular red line in the spectrum of cadmium. For this purpose again the interferometer was brought into use and a most accurate determination yielded the result that one meter is equivalent to 1,553,163.5 wave lengths of this particular red cadmium line. And now we may rest assured that even though the standard meter of Paris be destroyed by war, by vandalism, or by natural causes, it could be again reproduced to within an accuracy of at least one part in three million. It is a remarkable thing and a fortunate one that the wave lengths of any element such as cadmium are identical the world over and probably throughout the entire universe.
From this brief resume of Professor Michelson’s achievements it may be concluded that their distinguishing feature is precision. The economic value of these experiments of precision cannot be estimated in numbers but their use in promoting useful and properly directed thought is inestimable, and an interesting discussion of these uses has recently been given by Professor Millikan in Science for May 10, 1929. Certainly of greatest importance, in my mind, is the ether-drift experiment which triggered off the study of relativity, which in turn has promoted thought along the lines of atomic structure, has introduced the notion that energy is intimately related to mass, and has finally led to exceedingly interesting speculations as to the constitution of stars. Knowledge along this line certainly seems worth while in that possibly our future source of energy may be the stars, or, in particular, the sun.
As the Copernican theory led mankind away from geocentric ideas, so has the theory of relativity led him away from egocentric ideas, that is to say, one can no longer honestly estimate velocities and accelerations with respect to himself but must also extend to other stars and even other universes the privilege of being the basis of reference. A most entertaining and illuminating discussion of this subject is to be found in Eddington’s recent book, The Nature of the Physical World.
To conclude this description of Professor Michelson’s researches without mention of those which distinguish him as an artist as well as a scientist would be an unfortunate omission. Professor Michelson claims to have first learned to sketch at the Naval Academy, and later practiced a bit in oils and water colors. In recent years, however, he has spent his efforts only in water colors and in January of 1928 an exhibition of some of his work, or shall we not say pleasure, was sponsored by the Renaissance Society of Chicago.
These valuable scientific researches in themselves stand as evidence to the skill and mental prowess of Professor A. A. Michelson as an investigator, and the U. S. Naval Academy may well be proud to count him as one of its graduates; but these researches are apparently not the last, and the results of the three tasks which Professor Michelson, at the age of seventy-six, has set for himself, are awaited with genuine interest by the world at large.
Postgraduate School, U.S. Naval Academy, Annapolis, Md., Sept. 1, 1929
[1] 18 Jan., 1929.
[2] Fiske, From Midshipman to Rear Admiral, p. 15.
[3] Admiral Worden was then superintendent of the Academy, and formerly commanding officer of the ironclad Monitor.
[4] Nature, 18, 195 (1878).
5 This article has recently been republished in the Scientific Monthly for December, 1928.
6 Michelson, Astrophysical Journal 60, 260 (1924).