produced in Iron Wires by Magnetization. 355 



Shelford Bidwell. When the relation is expressed between 

 change of length and intensity of magnetization, the curve 

 takes the very different form given by fig. 3, B. The wire 

 slowly increases in length until an intensity of about 800 is 

 reached. From that point until a maximum length is attained, 

 at an intensity of 1200, the elongation is more marked. After 

 reaching this maximum it rapidly contracts ; the last portion 

 of curve being approximately a nearly vertical straight line. 

 The figure also shows that the point of maximum length does 

 not correspond to the point of greatest permeability of the 

 iron, as is seen by comparing this curve with the curve for 

 permeability plotted on the same figure. 



It is now necessary to make correction for the contraction 

 due to the B 2 /87r force. This contraction is obtained from 



the formula 



M V 1Q 7- BVStt 



I ~ M ' 



where M is the modulus of 



elasticity. My apparatus was well fitted for measuring the 

 latter quantity. A weight of about five kilograms was hung 

 on the wire and the elongations due to the additions of weights 

 of 20, 50, and 100 grams were read. From these Young's 

 Modulus was calculated in the usual manner. It was found 

 to be 2*2 x 10 12 for the specimen used. The contractions due 

 to the B 2 /87r force were then calculated and are given in 

 column 6 of Table I. 



Table I. 



H. 



384-8 



1. 



B. 



~ (obs.). 



dl /B 2 \ 



dl . ■ 

 j (corr.). 



4-6 



141 



1770 



-+- 010 



- 0-7 



4- 0-80 



73 



507 



294 



3700 









10-5 



752-4 



623 



7900 



116 



11-3 



12 16 



11-8 



733-0 



700 



8800 









12-8 



726-7 



739 



9300 



2-71 



1565 



18 33 



15-5 



695 



856 



10770 



5-71 



20 98 



26-69 



197 



6270 



981 



12350 



1471 



27-60 



42-31 



242 



541-4 



1041 



13100 



18-78 



31-05 



49 83 



28-8 



482-7 



1104 



13900 



22-92 



34-95 



57-87 



37-6 



389 1 



1163 



14630 



25 55 



38-53 



6413 



53-0 



286-3 



1203 



15170 



24-78 



41-69 



66-47 



60-4 



253-7 



1214 



15320 



23-23 



42-47 



6570 



67-7 



227-7 



1222 



15410 



21-30 



42-96 



64-16 



80-0 



193-8 



1228 



15500 



18-74 



43-46 



62-iO 



93-3 



167-2 



1235 



15600 



15-49 



4402 



59-51 



103-8 



150-8 



1238 



15650 



12-81 



44-30 



57-11 



111-6 



140-7 



1241 



15700 



11-03 



44 59 



5562 



121-2 



1300 



1244 



15750 



9-20 



44-88 



54-08 



145-4 



1096 



1257 



15930 



5-42 



4590 



51-32 



159-1 



100-6 



1261 



16010 



4- 194 



46 37 



4831 



186-5 



86-9 



1274 



16200 



- 2-91 



47-47 



44-53 



2103 



77-8 



1281 



16360 



697 



48-42 



41-45 



2469 



67-1 



1299 



16570 



12-97 



49-67 



36-70 



260-6 



639 



1304 



16650 



1665 



50-15 



3330 



2 B2 



