March 3, 1905.] 



SCIENCE. 



339 



On the Theory of Experiments to Detect 

 Aberration of the Second Degree. Ed- 

 ward W. MoRLEY, Western Reserve Uni- 

 versity, and Dayton C. Miller, Case 

 School of Applied Science. (To be pub- 

 lished in the Proceedings of the Amer- 

 ican Academy of Science, and in the 

 Ph ilosophical Magazine. ) 

 In this paper there is a reconsideration 

 of the simple theory of aberration of the 

 second degree as given by Michelson and 

 Morley in 1887, and of the general theory 

 as given by Hicks. The effects due to aber- 

 ration of the first, second and higher de- 

 grees have been computed, and the results 

 are shown in curves. The conclusion is 

 that the original theory was correct and 

 sufficient, and that the modifications pro- 

 posed by Hicks are effective in aberration 

 of the third or fourth degree only, or are 

 (in two instances) due to errors in his 

 theory. 



Report of an Experiment to Detect Change 

 of Dimension of Matter Produced by its 

 Drift through the Ether. Edward "W. 

 Morley and Dayton C. Miller. (To 

 be published in the Proceedings of the 

 American Academy of Science, and in 

 the Philosophical Magazine.) 

 The paper describes a large interferom- 

 eter designed for the measurement of ether 

 drift, and for the determination of any 

 differential change in the dimension of 

 matter, resulting from such a drift. The 

 support of the optical parts is a steel truss- 

 pattern cross, v/hieh is circumscribed by 

 a square with diagonals fourteen feet long. 

 By repeated reflections the optical path of 

 the light is lengthened to two hundred and 

 eleven feet. The whole interferometer is 

 floated on mercury to render observations 

 possible in all azimuths. The distances 

 apart of the mirrors are detennined by in- 

 terchangeable rods, which may be of any 

 suitable material. Experiments have been 



made using pine distance pieces, which give 

 results in accordance with those of the 

 original experiment made by IMichelson 

 and ]\'Iorley in 1887 in which the distances 

 were determined by sandstone. 



The theoiy given in the preceding paper 

 indicates a displacement of the interference 

 fringes due to ether drift amounting to 

 1.53 wave-lengths, as the apparatus is 

 rotated. The observations from 260 rota- 

 tions show that the displacement is less 

 than 0.015 wave-length. As the latter 

 quantity is as small as the errors of obser- 

 vation, the conclusion is that there is no 

 drift of the ether at the place where the 

 interferometer is mounted. 



Becent Experiments and Theories on the 

 Ether Drift. D. B. Brace, University 

 of Nebraska. 



The Elimination of Gas Action in Experi- 

 ments on Light Pressure. G. P. Hull, 

 Dartmouth College. (To be published 

 in the Philosophical Magazine and in the 

 Physical Review.) 



When light is thrown on one vane of a 

 torsion system suspended in a partial 

 vacuum, the ' Crookes effect' or gas action is 

 eliminated, leaving only light pressure 

 effective, in the following ways: (1) By 

 making the vane accurately vertical; (2) 

 by enclosing the absorbing or reflecting sur- 

 face; (3) by making the vane a cylindrical 

 surface having its axis coincident with the 

 suspending fiber; (4) by using inclined 

 surfaces and polarized light. 



Experiments are described and data 

 given showing that the gas action is elimi- 

 nated through large ranges of air pressure 

 varying from about half an atmosphere up 

 to a few millimeters of mercury. 



A simple lecture room experiment is de- 

 scribed for demonstrating that light pres- 

 sure on a reflecting surface is greater than 

 that on an absorbing surface in the ratio 



