510 



Mr. J. Trowbridge on Damping of 



oscillation, and L the self-induction. The ratio of one dis- 

 charge to the nth. one after it is 



rT 



e n zL' 



If we assume, — and it is a large assumption, but one which per- 

 haps the result will in some measure justify, — that the ratio of 

 the strength of the first to the strength of the last visible dis- 

 charge is more or less a constant, we may make use of the above 



T 



data. Denote ^j ^J A, and call the unknown resistance of 



the short connecting lead wires and of the spark x. Then 



will r = R' + * 



visible. 



Take cases (1) and (2), large copper and large German 

 silver wires, 



n 1 (R' 1 + ^) =n 2 (EI 2 + x), 

 9-5 ('M + x) =3(9-2 + *), 

 x = 3'A ohms. 

 Taking cases (1) and (4), large copper and small copper, 



will be the number of complete oscillations 



similarly 



n,(R , 1 + *) =n. 4 (R' 4 + #), 



9-5 (-66 + *) =5 (3-5 + *), 



x = 2'6 ohms. 



Experiments with other copper wires having R/ equal to 3*4 

 and 1*27 gave 5 and 8 for the values of n respectively, or 

 * = 2*4 ohms. 



The resistance (R/) of the lead wires forming part of x was 

 *8 ohm, leaving as a possible ^value for the resistance of the 

 spark about 2 ohms. 



If taking this value of x we calculate the value of R' 

 necessary to damp out the oscillation in one complete double 

 discharge in the case of the large iron wire, we shall have 

 9*5(-66+-3)=.l(R , + 3), 

 R' = 30 ohms. 



But neglecting the magnetic property of the iron, its cal- 

 culated resistance to alternating currents of this periodicity 

 was R / = 2*78 ohms. This is obviously inadequate and would 

 point to the conclusion that the oscillation is not, as some- 

 times stated, too rapid to admit of the magnetic action of the 

 iron. 



If we substitute this value R' = 30 in the equation 



R'= sl\ffK, 



