﻿438 Mr. C. E. St. John on Wave-lengths 



of the wave-length when iron displaced copper must be caused 



by an increased self-induction due to the magnetic properties 



of the iron. This implies that the magnetization of iron can 



be reversed 115 million times per second. This reduced the 



"time lag" of magnetization to very narrow limits, if forces 



of such duration can magnetize the iron. 



In the case of extremely rapid oscillations Prof. J. J. 



Thomson has shown { l Recent Re&earches in Electricity and 



2 

 Magnetism/ sec. 295) that approximately y 2 ~Yjni wnere 



T-^is the square of the frequency, and L' is the self-induction 



for very rapid oscillations and C the capacity of the system. 

 It is easy from this to calculate an approximate value for the 

 ratio between the self-induction per unit length of the iron 

 and copper circuits. 



Let L = the self-induction of the copper per unit length. 

 L'= „ „ < „ iron ^ „ „ 



= the capacity of either per unit length. 



Using as a basis of calculation the data from the third 

 maximum of the curves in fig. 4, PL XII., the total length 

 of the copper circuit (diameter 0*1201 centim.) is : — 



The sides, 562*5 x 2 =1125 centim. 



The closed end = 30 „ 



The equivalent of the end capacities 62 x 2= 124 „ 



1279 centim. 

 For the wire (diameter 0*1186 centim.) the length is : — 



The sides, 553 x 2 =1106 centim. 



The closed end = 30 ,, 



The equivalent of the end capacities 61 x 2= 122 „ 



1258 centim. 

 Since the two circuits have the same frequency, the pro- 

 ducts of the self-induction and capacity are equal. 

 1258 2 L'C = 1279 2 LC, 



£=1.034. 



In the same manner, for 



{Copper (diameter 0*08840 centim.). L r __ 1 n . - 

 Iron ( „ 0*08847 centim.), L 



f Copper (diameter 0*07836 centim.), 1/ __-, n , Q 

 tlron ( „ 0*07850 centim.), j^- 1 '^- 



