708 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



not the same in the two B diagrams, the general shapes of the curves are 

 very similar. 



Tliese two pieces of steel and the cast iron vpere then placed in the 

 solenoid mentioned above, the ends of each piece were connected to- 

 gether outside the coil by a massive iron yoke, and a current of about 

 45 amperes was sent through the coil ; the residual moments of the cast 



Figure 1. 



iron, the steel chilled in water, and the steel hardened in the special 

 bath were tlien about 4390, 5500, and G220. The weiglit of each piece 

 of steel was approximately 274 grams. Of three other pieces of steel 

 of a brand used exclusively by well-known m.ikers of magnets for 

 " magnetos," the first was liardened in jdain water, the second treated 

 witli potassium ferrocyanide, the third chilled in I\Ir. Thompson's bath. 

 These pieces, like those just described, were 18 cm. long, 2 cm. wide, 

 and 1 cm. thick, and they retained, after being magnetized to saturation, 



