Of arts and sciences. 293 



XXV. ' 



CONTRIBUTIONS FROM THE PHYSICAL LABORATORY OF 



HARVARD COLLEGE. 



No. X. — DISTRIBUTION OF MAGNETISM ON ARMATURES. 



By Harold Whiting. 



Presented, May 10, 1876. 



The subject of the distribution of magnetism on armatures has not 

 yet been carefully investigated ; although the change of form of the 

 curve due to the addition of an armature has been roughly determined. 

 It ap23ears, that, when an armature is added to one end of a magnet, 

 some of the magnetism spreads over the nearest part of the armature. 

 To prove this, and at the same time to get a general idea of the best 

 way to investigate the subject further, I performed the following pre- 

 liminary experiment. My apparatus consisted of a steel rod. half a 

 metre long and about a quarter of an inch in diameter, and an iron 

 rod of the same dimensions ; also a small wooden bobbin wound with 

 about a hundred and fifty coils of fine insulated wire, and having a 

 hole in its axis just large enough to allow it to slide freely over the 

 rods. A paper scale, graduated into centimetres and millimetres, was 

 attached to each rod. The two ends of the coil of wire were connected 

 with a very delicate galvanometer. The steel rod was magnetized. 



The coil was now slipped in different parts of the rod, over a dis- 

 tance of two centimetres each time, and the deflections were noted. 

 This deflection was made the ordinate of a curve, and the abscissa was 

 taken equal to the distance of the centre of the coils at the central 

 point of their motion. 



Table I. gives the figures, which are, of course, only relative. The 

 distances are given in centimetres. 



