Eutherford. — On the Magnetization of Iron. 491 



show that a leyden-jar discharge is oscillatory, and show also 

 the rapid decay of the amplitude of the vibrations. 



A method of deducing the ratio of the second half-oscilla- 

 tion to the first will be given later. 



The subject of the decay of amplitude of the vibrations of 

 a leyden-jar discharge is of considerable interest, especially in 

 connection with the resistance of spark-gaps and the radiation 

 of energy into space. 



Let L = self -inductance of discharge circuit for rapid alter- 

 nations ; 

 C = capacity of condenser ; 

 V = potential of jar ; 



E = resistance of connections and spark-gap to the 

 discharge. 

 Then the current j at any instant is given by 



E -t 



CV ~2L • * 



J = TTT^i e sm - 



(LC)* * (L G)» 



The exponential factor only includes the case of frictional 

 dissipation of energy, and does not take into account radia- 

 tion into space. In the experiments at present considered, 

 where the condenser is a leyden-jar, the lines of force of 

 which pass from one coating to the other, there can be a 

 very small amount of dissipation of energy due to radiation 

 (" Eecent Eesearches," J. J. Thomson, p. 482). We can 

 obtain a fairly accurate estimate of the decay of amplitude 

 of the vibrations from the experiments of eating away of 

 needles by HNO s , but a more useful estimate may be ob- 

 tained from considerations of the lOss of magnetism of a needle 

 as determined by a magnetometer. 



Two small oppositely-wound solenoids, A and B, were 

 placed in series connecting the coatings of an ordinary ley- 

 den-jar discharging through a spark-gap of j*gin. Two steel 

 needles similar in all respects and magnetized to saturation 

 were taken and placed in the solenoids A and B, so that their 

 north poles faced in the same direction. 



Plate XL VIII., Fig 6. 



When the leyden-jar was discharged through the spark- 

 gap the first half-oscillation tended to magnetize the needle in 

 A to a greater extent ; but, as it was practically saturated, no 

 effect was produced. The second half-oscillation tended to 

 demagnetize the needle, the third half-oscillation to magnetize 

 it again, and so on. 



On the needle in B, however, the first half-oscillation pro- 

 duced its full effect in demagnetizing, the second half tending 

 to magnetize again, and so on. 



