PEIRCE. — MAGNETIC BEHAVIOR OF HARDENED CAST IRON. 361 



may alter the field in the neighborhood of the test piece very sensibly. 

 An isthmus piece of steel which had been hardened unequally might 

 warp the field sufficiently to make the observations of the permeability 

 wholly erroneous. 



TABLE IX. 

 Cylinder of Hard Crescent Drill Rod. 



After much consideration I have decided not to print the results of 

 my measurements upon isthmus pieces of glass-hard Stubs and Crescent 

 Drill Rod for the reason that the maximum values of I seem to be rather 

 too high. In one case, indeed, the effect of hardening an isthmus piece 



TABLE X. 

 Cylinder of Hard Stubs Drill Rod. 



of steel was to make the ultimate value of I rather greater than before, 

 though for moderate excitations the permeability was less. I hope to 

 try soon the effect upon the uniformity of the field about the isthmus 

 of harder jaws. The results obtained with the hard cast iron seem to 

 be good. 



The cast iron used for the observations recorded below, which was 

 extremely soft and easy to work, came from the Broadway Iron Foundry 



