Peirce — Permeabilities and Reluctivities for Steel. 283 



inch inside diameter made by the American Tube Works. 

 The solenoid was mounted on a long oak truss which kept it 

 from buckling. 



Every specimen was tested in the solenoid several times 

 over to make sure that the demagnetizing process was so 

 effective that at low excitations, where differences are often apt 

 to appear, the same results were obtained at every trial. Until 

 the Xorway iron had been specially annealed, it was impossible 



Fig. 7. 



F 



* 



























U.I 

























* 



C 

























f 

























s 

 s 



s 

 s 



r 

























s 



/ 























J 



s 



s 



r 

























s 



/ 

























> 



* 



s 

























J 



s 



f 

























j 



* 



s 



























G 

























1 

























20 



50 







Fig. 7. This curve shows the reluctivity of the annealed Norway iron for 

 values of H between 100 and 2200. 



so to demagnetize the rod that for low currents the induction 

 should always be exactly the same. As Shuddemagen* has 

 shown, the "end correction" for a round straight rod is a 

 function of the absolute dimensions of the rod and not merely 

 of the ratio of the length to the diameter, but the correction 

 in the case of a half -inch rod of the length' used in the work 

 here described, is very small. 



No other explanations seem necessary to make the following- 



tables intelligible. 



* Shuddemagen, Proc. Amer. Acad. 

 DuBois, The Magnetic Circuit, § 31. 



Arts and Sciences, xliii, 190" 



