PEIRCE. — MAGNETS OF HARDENED CAST IRON. 



713 



Strengths be sent through this wire, the relative values of the whole mag- 

 netic induction across a given area betvireen the poles can be determined 



Figure 6. 



with sufficient accuracy by pulling out, from a definite position between 

 the jaws, a coil of suitable shape made of very fine manganine wire and 

 connected with a ballistic galvanometer. 



Figure 7. 



In this way diagrams may be obtained very like the C- and D-curves 

 of Figure 3, according as the casting is soft or hard, and this is a very 



