474 Prof. D. B. Brace on the Resolution of Light into 



On examining with a nicol, the central band was found not 

 to chnnge in intensity as the nicol was rotated, but the outer 

 bands appeared to be plane-polarized (or nearly so), since the 

 one was extinguished when the principal plane was 45° with 

 the plane normal to the field, and the other when it was 

 rotated through 90°. 



In order to study better the polarization of the doublet, a 

 single slit 0*2 millim. wide was used to obtain more light. 

 On each side appeared diffraction-bands,— some very fine. 

 When the circuit was made the image and all the bands, which 

 were sufficiently fine, broke up into doublets. 



On referring to fig. 4, it will be seen that the rays a x and a 2 

 after the last reflexion pass through the mica plate. This, 

 with the reflexion, produced a change of phase of slightly 

 less than §\, so that they were slightly elliptical, but nearly 

 plane-polarized. When the principal plane of the nicol was 

 turned 45° to the left, the image on the right was cut out, 

 and when turned 45° to the right of the vertical plane the 

 image on the left was cut out. This indicated that the ray on 

 the right was right-handed, and that on the left left-handed 

 polarized after the last reflexion. Thus, the ray on the right 

 had the same direction of vibration before the last reflexion 

 as the Amperian currents, the direction of the lines of force 

 being from right to left as indicated in the figure. Conse- 

 quently, vibrations in the direction of the Amperian currents 

 are accelerated (in phase or velocity), and those in the oppo- 

 site direction are retarded by the same amount. This corre- 

 sponds to the results which I obtained by the method of inter- 

 ference referred to at the beginning. On reversing the field 

 the direction of polarization of « t and a 2 was interchanged, 

 i. e. rotated through 90°, indicating that now a ± was right- and 

 a 2 left-handed. 



On tilting the prism so that the number of complete 

 passages w 7 as reduced from five to four, the image was 

 broadened and barely resolvable into two when the current 

 was thrown on. On tilting still farther, for three complete 

 passages, resolution was impossible, but a blurring or broaden- 

 ing at the edges of the image could be detected. Since the 

 incident ray a was unpolarized, we must conclude from this 

 experiment that only circular vibrations can be transmitted 

 along the lines of force, any disturbance being broken up 

 into its opposite circular components when propagated in a 

 magnetic medium. 



Different arrangements of the prisms were used, such as 

 sliding one over the other until the diagonal faces were 

 exposed, and sending in the ray nearly normally to these, but 



