184| Michelson and Morley — Feasibility of Establishing 



The square of the ratio of two successive measurements on 

 the mirror farthest from the reference plane will be the re- 

 quired result, and should agree, except in sign, with the cor- 

 responding result for the nearer mirror. 



The following is a specimen observation : 



March 12. A Sodium, T= ]7°-0, B = 74-55 cm 



Upper Mirror. Lower Mirror. 



557 zero 542 



274 zero 600 



572 zero 554 



260 zero 588 



Means 564 267 548 594 



564/ \594/ 



0-22 — ( ^^ )= —0-86 =+ 0-14 



0-14 



Final mean = 0*18 



— 0*19 = corrections for therm., barom. and phase. 

 Final result = -99 



The mercury light was obtained by passing sparks from an 

 induction coil through an " end on " vacuum tube enclosed in 

 a galvanized iron box heated by a Bunsen burner. Before 

 passing to the refractometer it was analyzed by a single carbon- 

 disulphide prism. By moving the source, yellow, green, or 

 violet light could be examined at pleasure. 



The comparison of intermediate bars is effected as follows : 



The bar, B, let us say, is held on a fixed support attached to 

 the bed of the comparer, and A is held on a movable carriage 

 so that the two are side by side with their lower mirrors in the 

 same plane. The reference plane is adjusted to make a small 

 horizontal angle with the surfaces of B (the vertical angle be- 

 ing adjusted to zero) and then the surfaces of A are adjusted 

 to parallelism with B. The carriage holding the combination 

 equivalent to the " reference plane " is then released from all 

 contact with adjusting screws. The fringes in white light 

 under these conditions are vertical lines on the lower surfaces. 

 The distance (in fractions- of a fringe) between the central 

 black fringes and marks on each mirror is noted. 



The reference plane is now moved back till it coincides with 

 the upper mirror on A when the fringes in white light appear 

 on this surface and the position of the central black fringe is 

 again noted. 



Next A is moved back till the lower mirror coincides once 

 more with the " reference plane " and finally the latter is moved 



