[ 342 ] 



XLIII. Observations on Light Propagated in a Dielectric 

 Normal to the Lines of Force. By D. B. Brace, Ph.D., 

 Professor of Physics, University of Nebraska * . 



[Plate IV.] 



THE following experiments were made to determine the 

 effect upon polarized light of a transparent medium in 

 a magnetic field. 



The observation of an effect upon polarized light in a 

 transparent medium in an electric field, suggests a similar 

 condition in a magnetic field. The state of polarization of 

 such media should affect, to a greater or less extent, the 

 propagation of polarized light. In magnetically polarized 

 media, the Faraday effect is always present except for propa- 

 gation exactly at right angles to the lines of force, a con- 

 dition impossible to realize for any finite stream of light. 

 Even with very small divergence of the rays this might mask 

 any new effect. In any case the Faraday effect must be 

 eliminated. 



The magnet used was forged from Norway iron. The cores 

 are 8 in. in diameter and 36 in. long. These are bolted to a 

 horizontal bed-plate. The movable pole-pieces are 8 x 8 x 13in. 

 and drilled to receive various pole terminals. Each core is 

 surrounded with three coils, each having about 1100 turns of 

 No. 10 wire, making approximately 650 pounds and 21 ohms 

 resistance. The six coils may be thrown into any combination 

 by a commutator. The total weight of the magnet approxi- 

 mates 4000 pounds. 



A Lippich half-shade polarizer was used, an image of the 

 sun being thrown upon it and observed with a telescope 

 through the analyser._ The image, which appeared elliptical, 

 was kept in the middle of the field so that it was bisected. 

 While the difficulty of maintaining these conditions was con- 

 siderable, the sensibility was several times that of any other 

 source. 



In the first experiment, a plate of Faraday glass, index 

 1*76 D and 166 x 170 X 15 mm. was used. The ends were 

 silvered so that a ray could be reflected any number of times. 



This w T as placed between the poles of the magnet and 

 adjusted to allow a varying number of reflexions of the ray, 

 making from 5 to 11 passages, or a total distance of from 

 •8 m. to 1*8 m. 



With the plane of polarization at 45° to the lines of force a 



* Communicated by the Author. 



