REPORT OF AN EXPERIMENT TO DETECT THE 

 FITZGERALD-LORENTZ EFFECT. 



By Edward W. Morley axd 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 examiue this ques- 

 tion. 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 sup- 

 ports 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 compensat- 

 ing 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 partis reflected 



* On the Relative Motion of the Earth and the Luminiferous Ether. A. A. 

 Miehelson and E. W. Morley. Am. Jour. Sci., 34, 333. 

 vol. xli. — 21 



