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L. M. Cheesman— Measurement of Electric Currents. 119 
always had a determined position, which it would not have 
had did the currents employed in any way alter the permanent 
magnetism of the needle. The results of the experiments in 
both of the above particulars were sufficiently favorable to 
warrant the hope that after a few changes a practical instru- 
ment based on the above principle could be made. 
Description of Apparatus.—The following is the form of the . 
instrument finally adopted. The circular coils and metal parts 
connected with the damper of a galvanometer of Edelmann’s 
form were removed and in their stead were placed two coils, 
fe having 2200 turns of silk-covered copper wire (diameter 
25 i 
obtained with the above instrument depends on its not bein 
altered, except temporarily, by the action of the alternating 
currents. The effect of a magnetizing force on a magnet is, 
owever, in general both of a temporary and a permanent 
character; were induction in magnets always accompanied by 
this permanent change, the construction of a trustworthy in- 
