342 Scientific Proceedings, Royal Dublin Society. 



to the law of its variation, we can calculate the period it took to 

 pass, and its maximum electromotive force by comparing this re- 

 sult with that given by an ordinary balistic galvanometer. 



For instance, the secondary current at anytime in Eiuhmkorif's 

 coil may, to a first approximation at least, be represented by an 

 equation 



C = Co sin TT — , 

 1 



where Co is the maximum current, and T the whole time of flow. 

 The total current as given by the balistic galvanometer is 



Q = \CcU=Co 



T / 2 TC 



^mir^dt=~=^CoT=lTtQ. 



I TT 



The quantity given by the electrodynamometer is 



S=jC'cU= Co'l 8in'7r^dt = iCiT; 



therefore T = -5-^ and Co = — x. 



It is thus. easy to see that the comparison of these observations 

 would give a great deal of information about transient currents. 



