1885.] 



of some experiments of Frohlich. 



257 



face will be in that surface since the incident vibrations are 

 parallel to the surface, and thus p = 90. 



Re'thy has made his comparison with Frohlich's experiments 

 by putting the equation into the form 



tan <f> = a cos 8 + b sin 8 = c sin (8 + e) , 

 and then calculating c and e by the method of least squares. In 

 each series there are some sixteen or eighteen observations which 

 are sufficient for comparison with a formula containing two arbi- 

 trary constants. 



For the angles of incidence 25° and 85° the same values of c 

 and e were obtained from the two gratings, for the angle 55° the 

 values for the two were slightly different, but 55° is near the 

 polarizing angle for the glass used and the effects of elliptic polari- 

 zation observed by Jamin, Quincke and others come in. 



From Rethy's values of c and e I have calculated the values of 

 p and (p , the latter of which was independently observed for the 

 different cases by Frohlich. 



Thus the values of cp calculated on the assumption that Froh- 

 lich's experiments can be represented by the equation (1) and 

 determined directly from experiment do not differ very greatly, 

 and the differences throughout Rethy's Tables are quantities of 

 the same order as those shewn above. 



This close agreement would seem to indicate that we may 

 treat the motion of the ether particles on the interface, to the 

 degree of accuracy required for these experiments, as rectilinear, 

 while the results, as Rethy has shewn, are decisively against the 

 hypothesis that the vibrations lie in the plane of polarization. 



The calculated values of </> given above are also given by 

 Rethy in the course of his tables. 



