Eutherford. — On the Magnetization of Iron. 197 



In rapidly-oscillating fields, therefore, iron is magnetized 

 in open circuit. The rapid surgings in a conductor are quite 

 sufficient to demagnetize iron, and no complete circuit is re- 

 quired. The use of a sensitive detector as a means of investi- 

 gating waves along wires will be discussed later. 



It has been shown that iron still exhibits magnetic pro- 

 perties in fields of over 100,000,000 oscillations per second. A 

 needle may be magnetized or demagnetized in open circuit by 

 the oscillations set up in the wire. 



More detailed experiments on the absorption of energy by 

 iron cylinders and resistances of iron wires in rapidly-oscillat- 

 ing fields will now be entered upon. 



V. Absorption of Energy by Conductors. 



This subject has been treated mathematically and experi- 

 mentally by J. J. Thomson (" Eecent Eesearches,"' pages 

 321-326). He has there shown, by observing the effects of a 

 discharge on a specially-prepared vacuum-tube, that an iron 

 cylinder absorbs considerably more energy than a copper one. 

 The experimental method pursued here is entirely different 

 from Professor J. J. Thomson's, but the final results obtained 

 are the same. The results are also quantitative, while 

 Thomson's method only admitted of qualitative results. 



Plate XLIX., Fig. 13. 



An ordinary leyden-jar was discharged through a spark- 

 gap A. In the discharge circuit was a solenoid C, consisting 

 of about thirty turns, and 14cm. long, and about 1cm. in 

 radius. A small coil B of three turns was used as a 

 "detector" solenoid. 



The magnetized detector was placed on the small solenoid, 

 and about twenty discharges passed in one direction. The 

 deflection due to the needle was then steady, and remained 

 unaltered however many more discharges were passed. 



Suppose, for example, the deflection fell from 200 to 100. 

 The needle was again magnetized in a solenoid close at hand, 

 and another twenty discharges passed in the opposite direc- 

 tion. If in this case the first oscillation tended to magnetize 

 the iron and the second oscillation to demagnetize, the final 

 deflection would be higher, as the amplitude of the second 

 half-oscillation is less than that of the first. Suppose the 

 deflection fell from 200 to 150, the needle was again magnet- 

 ized and replaced. 



A cylinder of iron was then placed in the large solenoid, 

 and twenty discharges passed- — (1) In one direction, (2) in 

 opposite direction. In (1) the deflection fell from 200 to 103; 

 in (2) the deflection fell from 200 to 162. 



We see, then, that the effect of the iron cylinder in the 

 32 



