(B) 



RESEARCHES <>X MAGNETOSTRICTION. 



r 2(1+30) 



381 



W 



Sq-p 



2(1 + 30) ' 



r here /> = ^ — -a + 4zJr+:U- 



ri" 



«'+*».;,.,. **<i + , )+ft 



H 

 From (<•) and (/), we find 



//=(,;/, 3m ^ K 



nH I l.E 



As these coefficients depend on Young's modulus and on rigidity, 



it was necessary to determine these constants in the specimens of 



ferromagnetics used in these experiments. Young's modulus was 



determined in the usual way from the results of flexure experiments 



on iron and nickel rods already examined. The modulus of rigidity 



was found by measurement of the torsion produced by a known 



twisting couple. For calculating the rigidity from the torsion of a 



square rod, the following formula, due to Saint Venant," was used. 



,_. .. . _ _,. .,., 6 x Moment of the couple 



Modulus oi Jragidit;y = — , ,, , , ^ -r— ; — ; 7 — 7 : • 



& J i^4:-jX (side ot the square) 4 x angle oi torsion 



Thus we obtain 



For E (Yonng's modu] K(rigidity) Hulk-modulus ti 



Iron 2.10xl0 12 0.800xl0 12 1.88x10" 0.844 



Nickel 2.07X10 12 0.771xl9 12 2.l6xl0 is 1.082. 



] ). Saint Venant, Torsi n dt - 1 sm s, p. 39<J, is".."). 



