710 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



the rod in thousands of units. The L-curve was obtained with a soft 

 casting, the heavy K-curve with a casting of the same lot which had 

 been chilled from a high temperature in cold water. At the same time, 

 with this casting, were hardened two or three pieces of Crescent Drill Rod 

 of the same dimensions as it. These were naturally not exactly alike mag- 

 netically, but the best of them furnished the dotted K-curve of Figure 2 ; 



Figure 3. 



the others had a very little less retentiveness. The magnetic likeness of 

 the cast iron and the steel is worthy of notice. 



In Figure 3 the horizontal divisions represent, as before, the field in 

 tens of gausses, the vertical divisions the corresponding moments of the 

 specimens in thousands of units. 



The C-diagram was obtained with a soft casting 18 cm. long and 

 .95 cm. in diameter, the D-curve with a casting of the same lot hardened 

 by Mr. Thompson's methods. Another casting of the same set, hardened 

 at the same time, gave the continuous curve in Figure 4, while a piece 



