282 



Prof. J. A. Ewing and Mr. W. Low on the 



with the same stress as before (226 kilogs. per square centim.). 

 The last two curves are as nearly as possible coincident 



Fig. 4. 



a a a. Solid bar, no load. 



bbb. Bar cut and faced, no load. 



c c c. Solid bar, loaded. 



ddd. Bar cut and faced, loaded. 



2 4 6 8 10 12 14 16 18 2i) 22 21 20 k8 30 62 3 

 Magnetizing Force, <Q (C.G.S.). 



in the early portion, and again when the magnetization is 

 strong ; at intermediate values of 33 they lie somewhat apart, 

 the divergence corresponding to a value of about 0*0009' mil- 

 lim. for the maximum thickness of the apparent air-space. 

 The divergence of the curve ddd from ccc may be due, in 

 part at least, to some mechanical hardening of the metal in 

 the neighbourhood of the joint by the operations of cutting 

 and scraping (and tapping, to remove the bar from the block 

 in which the face was scraped) ; the form of the curve ddd 

 suggests this. The following figures relate to this bar in the 

 solid state and when cut with the surfaces faced, without 

 load : — 



