Rutherford. — On the Magnetization of Iron. 501 



On the addition of a carbon resistance of 8-5 ohms to the 

 discharge circuit, the fall of the deflection was — (1) From 200 

 to 103 ; (2) from 200 to 176*. 



Since the fall of deflection is the same in the two cases, 

 resistance of iron wire = 8 - 5 ohms + resistance of the copper 

 wire for that particular period. Now, from Lord Rayleigh's 

 equations, the resistance of copper wire in rapidly-alternating 

 fields is given by R' = J \ p l R, where I = length of wire, 

 and R is resistance of wire for steady currents. From know- 

 ledge of the period this may readily be calculated. The re- 

 sistance of the iron wire is therefore known. 



In order to determine the period very accurately, a plate 

 condenser was used with ebonite as the dielectric. The S.I.C. 

 of ebonite had been determined previously and found to be 2-2. 

 The capacity of the condenser was found, from calculation of 

 the size of the plates to be 460 electrostatic units. 



From knowledge of the data of the discharge circuit the 

 self-inductance can be calculated. (See Lodge's "Experiments 

 on Discharge of Leyden-jars," Proc. Roy. Soc, June 4, 1891, 

 p. 33.) 



The self-inductance L = 4278 ;_ 

 frequency n — 27rv / LG 

 = 3o xlO 6 ; 

 and p =%m = 2-1 xlO 7 . 



The effect of the increase of diameter of wires on the self- 

 inductance of the circuits is small, so that in all cases the 

 number of oscillations per second will be taken as 3,500,000. 

 When the resistances of iron wires of different sections were 

 being determined a copper wire of as near as possible the 

 diameter of the iron wire under consideration was placed in 

 the circuit. In the case of an iron wire - 22in. in diameter, a 

 lead pipe took the place of the copper conductor. 



After the calculated resistance of the copper wires for a 

 frequency of 3,500,000 had been added to the carbon resistance 

 placed in the circuit, the following is the table of resistances 

 observed : — 



