312 Prof. A. Kundt on the Electromagnetic Rotation 



employed for these experiments. The iron core, wrapped with 

 wire, was provided with conical, rounded, and perforated pole- 

 pieces. The poles were placed about 4 millim. apart. The 

 current, which was furnished by a Gramme machine, had an 

 intensity of about 16 amperes. The glass plate under exami- 

 nation with its metallic covering was placed midway between 

 the poles in a suitable holder, permitting both horizontal and 

 vertical displacement and rotation, as nearly as possible at 

 right angles to the direction of the rays of light which tra- 

 versed it. Sunlight was always employed. 



In order to measure the rotation produced by the film of 

 iron, cobalt, or nickel, a portion of the piece of glass not 

 covered with the electrolytic deposit of metal was compared 

 with a portion covered by the film, by determining first the 

 rotation produced by glass and platinum, and then determi- 

 ning the rotation due to glass, platinum and iron, cobalt, or 

 nickel. Usually the thin platinum layer produced no measu- 

 rable rotation; so that a portion of the glass covered by the 

 metallic deposit could be compared with a portion from which 

 the metal and platinum had been removed by means of acid. 

 Since the rotation produced by platinum and glass alone, or 

 by the platinum and gla^s together with the coating of iron, 

 cobalt, or nickel gave ri&e to a tolerably strong dispersion, 

 the adjustment was made in these experiments for the transi- 

 iion-tint between blue and red; so that the rotation was 

 determined for the mean rays of the spectrum. When not 

 otherwise specified, the rotation given in the following account 

 means the sum of the rotations in both directions produced by 

 reversal of the current. A rotation in the direction of the 

 amperian currents is further specified as positive, and that in 

 the opposite direction as negative. 



Iron. 

 Iron mirror No. 1. Brown, transparent. 



Rotation due to glass and platinum upon"! -. ^ 



reversal of current J 



Rotation due to glass, platinum, and iron +4 30 



Rotation produced by iron film . . . . +3 30 



Iron mirror No. 2. Very thin, light brown, transparent. 



Glass and platinum + 1 30 



Glass, platinum, and iron + 2 24 



Rotation due to iron +0 54 



