Kuthekford. — On the Magnetization of Iron. 493 



of the first and second half-oscillations were made under 

 varying conditions. A few of these are incorporated in a 

 "Note on the Eesistance of Spark-gaps," placed at the end 

 of this paper. 



The general result obtained was that for a spark-gap of 

 j3-in., and inductance of about 4,000 C.G.S. units in circuit, 

 the amplitude of the second half -oscillation was less than half 

 that of the first. 



As an example of a balance of the kind explained, when 

 2-15 turns per centimetre were on the one solenoid and 1-06 

 turns per centimetre on the other the effect on the needles 

 was exactly equal. 



amplitude of second half-oscillation) _ 106 _ (\.aqo 

 amplitude of first half-oscillation J 2-15 



or nearly one-half. 



If this rate of decay holds for succeeding oscillations the 

 return oscillation has only one-quarter of maximum value of 

 first oscillation. 



Plate XLVIIL, Fig. 7. 



The curve in Fig. 7 is a rough representation of the rapid 

 decay of the oscillations. If the rate of decay continues for 

 several oscillations the current will have a very small fraction 

 of its original maximum value. It has been shown how a 

 magnetized steel needle placed in a small solenoid may be 

 used as a detector of an oscillatory discharge, and also as 

 a means of determining the rate of decay of the oscillation. 



A series of different experiments was then undertaken to 

 show that iron possesses magnetic properties under the in- 

 fluence of all kinds of discharges. 



The needle was placed in a solenoid connecting the ex- 

 ternal coatings of leyden-jars A and B, arranged as in Lodge's 

 experiments on the "alternate path." 



Plate XLVIIL, Fig. 8. 



A and B are two leyden-jars connected in series through 

 the solenoid D. When a spark occurs at C there is an 

 impulsive rush of electricity through the solenoid D. The 

 steel or soft-iron wire placed in the solenoid exhibited the 

 same effect as when the discharge occurs in the ordinary 

 way. The wire was always demagnetized, and the loss of 

 magnetism was almost exactly the same as when the jars are 

 connected in series in the ordinary way and discharged. 

 There was the same rate of decay of amplitude also, and, 

 as far as regards the effect on magnetized needles, the impul- 

 sive discharge is of the same nature as the ordinary discharge. 



(2.) The needle was next placed in a small solenoid in series 

 with one of the long wires reaching from the coatings of the 



