﻿14 Most Effective Adjustment of an Induction-coil, 



of h' may be estimated if we know the ratio of the external 

 capacity C e to the total capacity 2 . If C e is small in 

 comparison with C 2 the approximate value of the latter 

 (obtained from equation (5) by neglecting the present 

 correction) may be used here. If the current in the secon- 



dary windings varies as cos ~, the charge per unit length 



TTZ 



will be proportional to sin ~, Hence the ratio of C to C a 



is equal to the ratio of 



/• h ' 2 n h ' 2 



1 sin f r .dz to 1 sin -^dz. 



Jh2 k Jo h 



C e ttJl 



c 2 = C0S 2Jr 



This determines h'/h, and we then have 

 L.. 



r -i r* +h/2 



L ]2 1 ( TTZ , 



r — = j \ COS yr^ 



L*21 ll J-h2 ,l 



2 h! . irh 



= - • T . sin ^ . 



In the present experiments C e is the capacity of the 

 electrometer and the spark-gap terminals, and this is about 

 one-sixth of the total secondary capacity C 2 , the value of 



which is already known approximately 7 . Hence cos ^m = ~ , 



and ~ =1-12, from which p? =1*10 .- . The effect of this 



correction is therefore further to reduce L 21 /L 12 by about 

 10 per cent. 

 Taking both corrections into account we have approximately 



L 21 /L 12 = -85ir/2 = 1'335, 

 from which by (5) 



C 2 = -000052 microfarad. 



The charge of the secondary circuit at the moment of 

 maximum potential is therefore 5'2 x 5*969 x 10" 7 C.G.S., or 

 31 . 10" 6 coulomb. If the whole of this charge escaped from 

 the terminals, in the form of a spark or other discharge, the 

 discharge current would be, at n interruptions per second, 

 rcC 2 V 2 . Further experiments are, however, required in order 

 to decide whether this complete discharge takes place, or 

 whether some of the electricity does not return through the 

 secondary coil and continue to oscillate in it. 



