416 C. JBa? , us — Torsional Magnetostriction in Strong 



Assuming that in the given curves, figure 7, the obliquity of 

 45° has been reached, then from two consecutive positions of 

 the wires relatively to the field (0° and 90°, 90° and 180°, etc.) 



the spurious effect may be 

 eliminated. The slope so 

 found, however, lies within 

 the errors of hysteresis, set, 

 and the errors of orienta- 

 tion and can not be consid- 

 ered more than an estimate. 

 For the mean slope indi- 

 cates an effect of but 'll 

 per 180° of twist, or 2 cra 

 of deflection for a scale 

 distance of over 5 meters. 

 Hence even in the strongest 

 transverse magnetic fields 

 the persistent increment of 

 rigidity remains small and 

 is negligible in comparison 

 with the spurious effects 

 encountered. 



6. After reaching this 

 unexpected result it seemed 

 necessary to verify it in 

 other directions. In the 

 first place the question oc- 

 curred whether compatibly 

 with figure 2, type I, the 

 effect of longitudinal magnetization was an increment of rigid- 

 ity in all metals. I therefore tested a nickel wire (length 41 cm , 

 diam. •048 cm ) in the longitudinal field by replacing the trans- 

 verse helix ,4, figure 3, by an ordinary helix. An example of 

 the uniform results is given by figure 8, _Z?, and bears this out 

 (current 4 amperes, load 150 grams, field 400 c.g.s. units). 



On the same diagram will be found the apparent effect,./?, 

 of circular magnetization produced by a current of about 2 

 amperes passed through the wire, freely suspended in air. 

 The obvious decrement of rigidity resulting seemed suspicious, 

 however, inasmuch as the deflection on making the circuit was 

 rapid and the return to zero on breaking, prolonged. This is 

 nearly what would occur if the observed decrement of rigidity 

 was due to heat alone. 



7. Final experiments were therefore directed to a compari- 

 son of the effect of a circular field in iron and the effect of a 

 similar field in brass, yielding it would appear a straightfor- 

 ward method of decision. In figure 9, I give a preliminary 



