4(j6 Prof. D. B. Brace on the Resolution of Light into 



and magnetic rotation to produce an observable resolution. 

 Instead, an analogous system was used by inserting a half- 

 wave plate between two prisms of Faraday glass, thus changing 

 the respective circular components to opposite ones. But 

 too much difficulty was experienced in obtaining the exact 

 retardation over a sufficient surface. Refraction near the 

 angle of total reflexion also gave imperfect resolution. 



In the present series of experiments different arrangements 

 were used. Instead of refracting across a surface from one 

 medium to another, the same thing may be attained by 

 reflecting from a surface into the same medium, providing 

 some of the components may be made to change their phase 

 by the proper amount (180°). This was attained in the 

 following experiment. Fig. 1 is the trace parallel to the 

 lines of force of a prism of Faraday glass placed between 

 the bored-out poles of a powerful electromagnet. This 



Fiff. 1. 



reflecting surface made angles of 66° with the polished ends 

 and was carefully figured and silvered. By shifting the pole- 

 pieces, the angle of incidence could be varied from 65° to 

 75°. Under an incidence of 72° there was a relative change 

 in phase of 90° approximately between the components in 

 and at right angles to the plane of incidence, due to the 

 reflecting silver surface. If now natural light is sent in, it 

 should be broken up into opposite circular components which 

 would be changed into linear vibrations at right angles to 

 each other at the surface, and these should in turn be broken 

 up into opposite circular components. Those components 

 which had the same direction of vibration as before inci- 

 dence would be reflected at the same angle, while those 

 oppositely circularly polarized would be deviated from the 

 medial ray. Three lines should thus have been produced 

 when the field was thrown on, the outer ones being 

 oppositely circularly polarized, and the middle line being 

 unpolarized and twice the intensity of each of the others. 

 Although the full resolving power of the aperture was 



