358 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



versing the exciting current of the yoke when L and M were opposed to 

 each other in the circuit of the ballistic galvanometer (V) described 



TABLE III. 

 Cylinder of Hard Cast Iron. 



above. When L alone was used in the galvanometer circuit, and 

 proper corrections for the air lines through L had been made by the 

 use of the H just determined, it was possible to measure the induction 

 flux in the metal. 



TABLE IV. 

 Isthmus of Hard Cast Iron. 



The second kind of specimen shown approximately by K, Figure 2, 

 was of the shape usually employed in isthmus measurements. Cast 

 iron differs from steel in that it can be heated so hot before it is chilled 

 that it becomes eventually hard throughout its mass, while steel can be 

 hardened only for a little distance from the surface. On the other hand, 



