Magnetic Permeability, $c., of Iron at Low ; Temperatures. 95 



Table VI. Variation of Permeability with Temperature. 

 Pianoforte Steel. 



Temperature measured in Platinum degrees by standard thermo- 

 meter Pj. 



Permeability. 



Temperature. 



- 



- 20 



- 40 



- 60 



- 80 

 -100 

 -120 

 -140 

 -160 

 -180 

 -200 



We propose to continue the examination of the anomalous behaviour 

 so presented by iron in different states of hardening by examining in 

 the same way the changes of permeability in the case of several iron 

 rings of the same dimensions formed in the one case of soft annealed 

 iron, and in another case of the same quality of iron hardened, and in 

 the remaining cases using steel of known composition at different states 

 of temper. We desire to add that in the conduct of this research we 

 have been under great obligations to Mr. J. E. Petavel for rendering 

 us very efficient assistance in taking the exceedingly tedious ballistic 

 galvanometer observations, and in reducing them when taken. 



VOL. LX. 



