454 Messrs. Rowland and Hutchinson on the 



.'. I =10-^ 5-46 H sin ^, 



^ = 10-* 5-46 H M2+E> si„ ^. 

 tan a ^ 



For measurement of H : — 

 Electrodynamometer, 



i — g -y^ Vsma. 



g = constant of windings = 10~^. 6*454 

 K = moment of inertia = 10^. 8*266. 

 T = time of one swing = 2*441. 

 .-. *■= 10-2.7-59 V^i"^. 

 Tangent galvanometer : — 



2 = 7^ tan S = , tan S. 

 (jT Z7rn 



n = no. turns = 10. 



I) = radius turns — 40"98. 



.♦. i = 0-795 H tan h, 



and, substituting the value of i, 



H = 10-2. 9-55 -Y^. 

 tan o 



Surface density (o-) : — 



o- is obtained from electrometer-i-eadings. 



V 



0" = 1 — • 



4zTTe 



V = Dx/^'. 



A 



A = corrected area of movable plate 

 = i7r.jRHEi2+...J=i7r{51-01}, 



V = 10 X 1-756 D V^^', 



and o-= 1-397— \/io. 



As soon as the attempt was made to electrify the appa- 

 ratus, difficulties of insulation were met with. ^ The chnrged 

 system was quite extensive, and the opportunity for leakage 



