322 Prof. A. Kundt on the Electromagnetic Rotation 



for the position of parallelism the direction of rotation is the 

 same for all incidences and opposed to the molecular currents, 

 while when the planes are at right angles the rotation changes 

 sign for an angle of ahout 82°. 



Our experiments also show a maximum rotation at 65°, as 

 Kerr gives. 



Second Series of Experiments. 



An exactly similar series of experiments was made with a 

 steel mirror of the same size, whose surface had been electro- 

 plated with nickel. The following values were obtained : — 



J. = J- 



20-0 



30*1 



o-o 



—1-7 



+ 0-0 

 + 1-8 



40-0 



—2-7 



+ 1-4 



50-0 



—4*7 



+ 0-3 



61-5 



—4-2 



— 0-7 



65-3 



75-0 



-3-8 



-1-1 



-2-2 

 -1-9 



With nickel also the direction of rotation remains the same 

 for all incidences — , but for the position J_ changes its sign 

 between 50° and 60°. 



The amount of rotation is, on the whole, perceptibly smaller 

 than with iron. This is in agreement with what was said 

 above as to the ratio of the rotatory power of nickel to that 

 of iron. 



In order to test whether any perceptible distortion or bend- 

 ing took place when the magnet was excited, the images of 

 a vertical and horizontal millimetre-scale were observed by 

 means of a telescope in the manner already described. When 

 the current was established, there occurred always a very 

 slight displacement, and also a small bending of the mirror. 

 The latter was inferred from the fact that the divisions and num- 

 bers of the scale between became somewhat indistinct. These 

 displacements and distortions were, however, extremely slight; 

 and the same whether the current was sent in the one direc- 

 tion or in the opposite. They could not therefore have exerted 

 any perceptible effect upon the observed rotations. Besides 

 the complete series of observations described, a large number 

 of separate observations were made with the various mirrors 

 under various conditions. They were all in complete agree- 

 ment with the numbers of the above tables. The following 

 may be quoted : — 



