Miller D.C. Ether-drift experiments at Mount Wilson // Science, Vol. LXI, June 19, 1925 — Page 620

Miller D.C. Ether-drift experiments at Mount Wilson // Science, Vol. LXI, June 19, 1925 No. 1590

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[Vol. LXI, No. 1590

In the summer of 1921 the steel frame of the interferometer was dismounted and a base of one piece of concrete reinforced with brass was cast in place of aluminum or brass, thus the entire apparatus was on the mercury float. All the metal parts were made free from magnetic effects and the possible effects due to heat were much reduced. In December, 1921, 42 sets of observations were made with the non-magnetic interferometer. These show a positive effect as of an ether drift which is entirely consistent with the observations of April, 1921. Many variations of incidental conditions were tried at this epoch. Observations were made with rotations of the interferometer clockwise and counter clockwise, with a rapid rotation and a very slow rotation, with the interferometer extremely out of level, due to the loading of the float on one side. Many variations of procedure in observing and recording were tried. The results of the observations were not affected by any of these changes.

The entire apparatus was returned to the laboratory in Cleveland. During the years 1922 and 1923, many trials were made under various conditions which could be controlled and with many modifications of the arrangements of parts in the apparatus. An arrangement of prisms and mirrors was made so that the source of light could be placed outside of the observing room, and a further complication of mirrors was tried for observing the fringes from a stationary telescope. Methods of photographic registration by means of a motion picture camera were tried. Various sources of light were employed, including sunlight and the electric arc. Finally an arrangement was perfected for making observations with an astronomical telescope having an objective of five inches aperture and a magnification of fifty diameters. The source of light adopted was a large acetylene lamp of the kind commonly used for automobile headlights. An extended series of experiments was made to determine the influence of inequality of temperature and of radiant heat, and various insulating covers were provided for the base of the interferometer, and for the light path. These experiments proved that under the conditions of actual observation the periodic displacement could not possibly be produced by temperature effects. An extended investigation in the laboratory demonstrated that the full-period effect mentioned in the preliminary report on the Mount Wilson observations is a necessary geometrical result of the adjustment of mirrors when fringes of finite width are used and that the effect vanishes only for fringes of infinite width, as is presumed in the simple theory of the experiment.

In July, 1924, the interferometer was taken again to Mount Wilson and mounted on a new site where the temperature conditions were more favorable than

those of 1921. The interferometer house was also mounted with a different orientation. Again the observations showed a definite positive effect corresponding to the observations previously made at Mount Wilson. The observations on Mount Wilson were resumed in March, 1925, and continued until about the middle of April, during which time 1,600 measures of the drift in 35 sets were made. Again many variations in detail of arrangement of parts and in methods of observing were made without in any way altering the result. Throughout the latter epoch of observations, the conditions were exceptionally good. Some of the time there was a fog which rendered the temperature very uniform. Four precision thermometers were hung on the outside of the house. On several occasions the extreme variation of temperature was not more than 0.1 degree and usually it was less than 0.4 degree. Such variations did not at all affect the periodic displacement of the interference fringes. The observations of April, 1925, give results almost identical with those of April, 1921, notwithstanding that the interferometer had been rebuilt and that a different system of illumination and different methods of observation were employed and that it was mounted on a new site in a house differently oriented.

The interferometer readings, being plotted, give directly by harmonic analysis (carried out with the mechanical harmonic analyzer) the azimuth and magnitude of the ether drift. There are no corrections of any kind to be applied to the observed values. In the work so far, every reading of the drift made at Mount Wilson has been included at its full value. No observation has been omitted because it seemed to be poor, and no “weights” have been applied to reduce the influence on the result, since no assumption has been made as to the expected result. It may be added that while the readings are being made, neither the observer nor the recorder can form the slightest idea as to whether any periodicity is present, much less as to the direction or amount of such periodicity.

The test of these observations is whether they lead to a rational and wholly consistent indication of a constant motion of the solar system in space, combined with the orbital motion of the earth and the daily rotation on its axis. There is a specific relation for a given latitude between the observed azimuth of drift and the sidereal time of observations. Observations at different sidereal times should show different azimuths and all observations at the same sidereal time should show the same azimuth for a given epoch. A preliminary graphical solution of the observations indicates that these conditions are fulfilled.

It need hardly be said that the determination of the absolute motion of the solar system from such interferometer observations is one of great complex

June 19, 1925]



ity. Professor J. J. Nassau, of the department of mathematics and astronomy of Case School of Applied Science, and Dr. G. Strömberg, of the staff of the Mount Wilson Observatory, have given very great assistance in the mathematical analysis, and have developed solutions of various parts of the problem, and also a complete least-squares solution of the general problem. A definitive numerical calculation will require several months of continuous work and is now in progress.

The ether-drift experiments at Mount Wilson during the last four years, 1921 to 1925, lead to the conclusion that there is a positive displacement of the interference fringes, such as would be produced by a relative motion of the earth and the ether at this observatory, of approximately ten kilometers per second, being about one third of the orbital velocity of the earth. By comparison with the earlier Cleveland observations, this suggests a partial drag of the ether by the earth, which decreases with altitude. It is believed that a reconsideration of the Cleveland observations, from this point of view, will show that they are in accordance with this presumption, and will lead to the conclusion that the Michelson-Morley experiment does not and probably never has given a true zero result. A complete calculation of experiments, to be made in the immediate future, should give definite indications regarding the absolute motion of the solar system in space.

Dayton C. Miller

Case School of Applied Science


With the decrease in the supply of game animals which has inevitably accompanied the close settling of our country by Europeans, it has commonly occurred to those interested to remedy the situation by importing and planting non-native species which it is thought might be more prolific or hardier than the native species. This idea at first thought is appealing, and it has seemed so reasonable to many game administrators that it has been tried over and over again both in our own state (I am writing from California) and in other states, at great public expense. Experiments of this sort within the state of California alone have entailed the expenditure of upwards of fifty thousand dollars, as shown by the printed reports of our California Fish and Game Commission. But, not one non-native game species has become established here to a degree of success warranting the declaration of an “open season” upon it.

It has just been announced through the public

press that our state fish and game commission, apparently forgetting all these past and unsuccessful experiments, has again under serious consideration a plan for raising in captivity and liberating certain non-native game birds; and the kind specifically mentioned is the Hungarian partridge. This announcement must bring dismay to every student of nature whose concern (as is my own) extends to include the welfare and usefulness to man of California’s wild life generally and is not restricted to objects of sport alone.

In the first place, it is believed by some thinking naturalists that the chances are decidedly against the success of this project—success as bringing the beneficent results expected of it by the gunner. To repeat, such experiments have already been tried,1 and these have involved no less than twelve nonnative game species and an aggregate of at least 13,000 individual birds, by record, liberated. No success has been achieved. Are chances of success now, with further depletion of natural food and cover, any better than before?

Howsoever, if the introduction now proposed should prove successful from the sportsman’s standpoint and, say, the Hungarian partridge become fully established, what would be the possible, even probable, results'? One result, about which there is no question whatsoever in my own mind, would be the crowding out, the supplanting, in partial measure if not altogether, of our native California quail.

An axiom which I think all close students of natural history would accept without reservation is as follows: No two species of identical or even closely similar biological predilections can long occupy the same niche or ecologic space at the same time. If the same food supply, in kind and amount, if the same type of shelter for roosting or resting, or if the same sort of breeding places be resorted to by two species, there will be inevitable conflict. One or the other species will give way, because bound to be at less advantage in some respect as to structural equipment or instinctive manner of reacting to the conditions about it. The Hungarian partridge and the California quail belong to two genera of gallinaceous birds within the same family. While there are undoubtedly some differences between these two birds in their ecological requirements, the general similarities are exceedingly close. More or less keen competition would be bound to operate sooner or later to the disadvantage of one of them. I, for one, hereby protest against any act that will likely jeopardize the existence of our native Califor-

1 See Grinnell, Bryant and Storer, "Game Birds of California,,, 1918, pp. 29 to 44.