REPORT OF AN EXPERIMENT TO DETECT THE
FITZGERALD-LORENTZ EFFECT.
By Edward W. Morley and Dayton C. Miller.
Presented May 10, 1905. Received May 19, 1905.
A null result was obtained in 1887,* in an experiment to detect, if possible, a difference of velocity of light in different directions owing to the motion of the apparatus towards or away from waves of light in the stationary ether. FitzGerald and Lorentz then suggested that the dimensions of the apparatus might be modified by its motion through the ether. If this modification depend on the resilience or other physical properties of the materials, it may perhaps be detected by experiment.
We have constructed two apparatus with which to examine this question. In the first, we replaced the sandstone used in 1887 by a structure of white pine. A strong cross was built up of planks, fourteen inches wide and two inches thick, and fourteen feet long. One was laid east and west, then one across it north and south, and so on. They were slightly notched where they crossed. On their intersection was secured a cast-iron bedplate for certain optical parts of the apparatus. At the ends, after filling the spaces between the planks, were bolted iron supports for our mirrors. The whole was placed on a round float, which in turn rested in a basin of mercury.
Our sixteen mirrors were each four inches in diameter. The mirrors rested each ou the points of three adjusting screws, against which they were held by springs. Ou the bedplate at the intersection of the arms of the cross were placed a plane half-silvered mirror and a compensating plate ; these had been, as is usual, cut from the same plane-parallel disk.
Figure 1 is a diagram, not to scale, of the optical arrangements. Light from a source S reaches the mirror D. Part is transmitted, reaching the mirror II. It is successively reflected to 2, 3, 4, 5, 6, 7, and 8. From 8 it returns by the same path to D, where part is reflected
* On the Relative Motion of the Earth and the Luminiferous Ether. A. A. Michelson and E. W. Morley. Am. Jour. Sci., 34, 333.
VOL. XLI.—21
322
PROCEEDINGS OF THE AMERICAN ACADEMY.
to the observer at T. Another part of the incident ray is reflected along the other arm of the cross, is similarly passed to and fro, returned, and at last transmitted to the observer. In the apparatus actually used, mirror 5 lay above 3, rather than to one side of it ; Figure 2 shows this arrangement. The whole path of the light along these mirrors was enclosed and covered, to lessen the effect of air currents and other local disturbances. An acetylene flame was carried as a source of
ror with its surface always parallel to a given surface. This we had avoided, in order to have everything about the two arms as symmetrical as possible.
We now computed the direction and velocity of the motion of the centre of the apparatus by compounding the annual motion in the orbit of the earth with the motion of the solar system towards a certain point in the heavens. During part of August, the whole of September, and nearly all of October, this motion never coincides with the plane of our apparatus. For other dates, there are two hours in each day when the motion is in the desired plane, except for two days when the two hours
light. A telescope magnifying thirty-five diameters gave distinct vision of mirror 8, at whose surface the interference fringes are apparently localized.
Figure 1.
Figure 2.
The mirrors, being silvered and polished, were put in place, and the lengths of the two paths were measured with a split rod and then made nearly equal. Establishing interferences in sodium light, we found the central part of a series of some seven hundred interferences which are brighter than the adjoining three hundred. With no long search, we could see interferences in white light, although we had provided no screw for moving a mir