CLOSED ELECTRO-MAGNETS. 29/ 



of the galvanometer is impelled, minus the weak current which 

 the primary spiral excited in the secondary. The current d 

 was, of course, opposite in direction to those which were caused 

 by the closing of the circuit. 



Wide keeper. Narrow keeper. 



i = sin 4° 25' =1-000. 

 «=+ 4-36 a= f 4-80 



A= +32-10 d= +20*77 



c= + 10-45 c=+ 9-58 



c?=-2501 ^=-- 14-77 



i = sin 5° 31'= 1-249. 

 ft'=+ 10-23 «'=+ 10-23 



^>'= +49-66 ^=+28-98 



c'=+ 17*99 c'= +17-13 



</'= -.84-75 6?'== -1713 



i=sin 10°21' = 2-.B35. 

 «"=+ 16-06 «"= + 16-06 



^"=+58-86 ^>"= +37-77 



c"=+ 24-15 c''= +22-04 



d"= -39-37 ^"= — 16-92 



In consequence of imperfections in the induction-galvano- 

 meter, these measurements do not possess very great exactness, 

 but they are sufficient to enable us to form a judgement of the 

 general facts of the case. 



Thus we observe that the current b, which is the most im- 

 portant here, is stronger than all the others, especially when 

 the galvanic current is weak, and that its increase with the 

 augmentation of the galvanic current is comparatively slow. It 

 evidently measures the total magnetism assumed by the magnet 

 in consequence of the united action of the keeper and the gal- 

 vanic current, and they are therefore stronger than the current 

 c, as this is due to the difference between the total and the 

 residual magnetism. The currents d are due essentially to the 

 residual magnetism, and if the permanent magnetism remained 

 unchanged by the separation of the keeper, we must have 

 A=c + c?. 



If it be correct that the currents b measure the total mag- 

 SCIEN. MEM.— Nat. Phil Vol. I. Part IV. Y 



