356 



Dr. L. T. More on the Changes in Length 



The last column of this table was found by taking the 

 difference between the observed elongation and the B 2 /87r 

 contraction. The relation between this corrected elongation, 

 due to what has been called the direct action of the magnetism, 

 and the intensity of magnetization is graphically shown by 

 fig. 3, A. The effect of this correction is to make the elonga- 

 tion much greater for a given intensity. The maximum value 

 of the elongation is more than twice as great as the observed 

 maximum. And the greatest intensity employed, 1300 C.G.S. 

 units, produces an elongation and not a contraction as ob- 

 served. 



No correction for the change in elasticity was made. For 

 the present case it would be insignificant. See discussion of 

 errors at end of this paper. 



Effect of Hardening. 



The effect of hardening the wire was next considered. A 

 piece of the same quality of iron was heated to a bright red 

 by passing a current through it, and then suddenly cooled. 

 After the operation the wire was much harder and only slightly 

 burnt on the surface. The observed changes in length, those 

 due to B 2 /87r, and the corrected values are given in Table II. 



Table II. 



H. 



I. 



B. 



f (obs.). 



I [Stt)' 



SI , , 

 - (corr.). 



V 



5-0 



8 



100 



-0-00 



-o-oo 



+0-00 



87 



53 



670 



0-05 



0-08 



003 



12-8 



272 



3420 



010 



2-12 



202 



183 



709 



8920 



0-20 



14-41 



14-21 



27-4 



923 



11620 



0-50 



24-44 



23-94 



36-6 



947 



11940 



0-70 



25-77 



25-07 



45-7 



1012 



12770 



1-85 



29-48 



2763 



57-2 



1044 



13180 



3-10 



31-42 



28-32 



685 



1060 



13390 



410 



32-42 



28-32 



965 



1074 



13600 



7-40 



33-43 



26-03 



118-8 



1064 



13490 



5-40 



3293 



27-53 



138-5 



1100 



13560 



(?) 15-00 



35 24 



20-24 



180-1 



1126 1 



14320 



24-20 



3711 



1291 



Hardening the iron makes the elongation smaller, and for the 

 present specimen, the least intensity of mnonetization caused 

 the wire to contract (fig. 4, B). The corrected relation be- 

 tween the change of length and the intensity is shown by 

 fig. 4, B'. On this figure is also plotted curve A, the same 

 relation, taken from fig. 3, for the wire when not hardened, 

 and curve A' shows the corrected relations for the same. 



