488 Transactions. — Miscellaneous. 



In the first experiment four leyden-jars were placed in 

 parallel ; the depth of penetration was found to be T troin. 



In next experiment two leyden-jars were placed in series ; 

 the depth of penetration was found to be 00035in. 



.'. in first case discharge penetrates 2 - 8 times the distance 

 of the second case. But the capacity in the first case was 

 eight times that in the second case ; v 7 8 = 2 - 8, and therefore 

 from this experiment we see that the depth of penetration is 

 : : al to the square root of the capacity. 



But from the equation of discharge of leyden-jar of capa- 

 city C through inductance L the maximum current is given by 



3 = (LC)4 ' 



where V is potential of charge, and E resistance in circuit. 



The maximum current varies therefore as a/G. The depth 

 of penetration is therefore : : al to the maximum current. 



II. Effect of Continued Discharges on the Magnetism 



of A Needle. 



it was observed that the magnetization of a needle was in- 

 creased by sending a large number of discharges in one direc- 

 tion. In all the experiments that follow, a uniformly-magne- 

 tized steel needle was used, and the effect of a discharge in 

 decreasing the deflection due to the needle was observed. A 

 uniformly-magnetized needle has many advantages over an 

 ordinary unmagnetized needle. These advantages need not be 

 discussed at this point, for they will be sufficiently obvious as 

 the paper proceeds. 



A solenoid of a large number of turns was wound, and a 

 battery current sent through it sufficient to produce a field of 

 over 100 C.G.S. units in the solenoid. The steel needle was 

 thus practically saturated when required by placing it in the 

 solenoid and turning on the current. 



'D 



Plate XLVIIL, Fig. 5. 



The condenser is charged by Voss or induction machine. 

 In most of the later experiments an induction coil was used. 



A B is a solenoid of about three turns per centimetre placed 

 behind magnetometer. The needle was first saturated, and 

 then placed in solenoid A B at such a distance from the 

 magnetometer as to give a convenient deflection. When a 

 spark occurred at S the deflection due to needle in A B fell. 

 It was observed that the effect on the needle did not end with 

 the first discharge, but the deflection fell gradually for every 

 spark that passed, till finally the iron reached a steady state, 

 and there was no further change of deflection, however many 

 sparks were passed. 



