Kutherford. — On the Magnetization of Iron. 499 



(4.) Solid iron rod. Increase of impedance, 3-5 ohms. 



(5.) Copper cylinder, platinum cylinder, a test-tube filled 

 with CuS0 4 solution, gave no appreciable absorption of energy. 



(6.) A carbon rod, however, absorbed a large amount of 

 energy. Increase of impedance of circuit, 3'3 ohms. 



Table of Absorption of Energy by Various Conductors. (The absorption 

 of energy is proportional to the increase of impedance of the circuit.) 



Substance. 



Increase of Impedance. 



Laminated soft iron 

 Solid soft iron . . 

 Carbon cylinder 

 Copiier cylinder . . 

 Platinum cylinder 

 Steel filings 



10-25 ohms. 

 3-5 

 33 „ 



Not appreciable. 



9 - ohms. 



Professor J. J. Thomson (" Eecent Eesearches," pp. 321, 

 322) shows that the increase of impedance of the primary 

 circuit due to absorption of energy by an iron cylinder of 

 length I and radius a 



4tt 2 ZN 



* (XY a - 



where p = 2irn ; n being the number of oscillations per second ; 

 N = number of turns per centimetre cf solenoid ; 

 jx = permeability of iron ; 

 o- = specific resistance of iron. 



Now, we have shown that a soft-iron cylinder increases 

 the impedance of the circuit by 3'9 ohms. 



From this equation we can deduce a rough approximation 

 of the value of //. for iron in fields of high frequency. 



The number of oscillations per second was 2,000,000, cal- 

 culated from data of discharge circuit. 



o- is approximate for soft iron, 10 4 ; 

 I = 14cm. ; 

 a = 095cm. ; 

 N= 2, nearly. 



• 3-9 x 10' = ^ x 14 . (2)' ( fr-g-^-10* ) '0.95. 



An approximate solution of this is /a = 172, which shows 

 that iron has considerable permeability even under the in- 

 fluence of these very transient fields. 



It is interesting to observe that it is not necessarily 

 the best conductors that absorb the most energy in these 

 fields : in fact, the very reverse is the case. A copper cylinder 

 does not absorb more than one-fortieth of the energy that an 



