250 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



the rod surrounded by the other coils, to the induction at the centre. 

 Thus, suppose for a given constant H' we had obtained throws corre- 

 sponding to the central coil alone, and also for this coil when connected 

 in opposition to every one of the other coils in turn. In an actual case 

 we had for Rod B: H' =■ 59.5, the induction for the central coil was 

 B — 16,560, leakage between CD and MN was 630, and between 

 CD and X Y 7910, lines of induction per unit cross-section. From 

 these results we get for the actual magnetic induction through MN 



100 



10000 



Figure 24. 



Curves showing variations in the distribution of magnetic induction in rods 

 No. A and No. B. D = 1.905 cms. and m = 60. 



15,920 lines, and through X Y 8650 lines. Now, denoting the B 

 through the central coil at any time by 100 per cent, we shall have 

 96.3 per cent of this induction passing also through the coil M N, 

 and 52.3 per cent through X Y. These two numbers are therefore 

 plotted against B = 16,560. Figures 23, 24, and 25 exhibit all the 

 observations taken. The slight zigzag arrangement of the points is 

 due to the fact that the current did not stay quite constant during the 

 time of observing the throws from all the coils on a rod. All the rods 

 have been referred to previously by the same designations, except 

 (No. I), which is merely one of the enql-pieces cut from the long rod 



