374 



Mr. J. W. Gennnell. 



[Dec. 10, 



II. " On the Magnetisation of Steel, Cast Iron, and Soft Iron " 

 (being the investigation for which the Watt Prize of 1884 

 was awarded by the Senate of the University of Glasgow). 

 By John W. Gemmell. Communicated by Sir William 

 Thomson, Kt, LL.D., F.RS. Received October 31, 1885. 



The experiments, of which the following is a description, with their 

 results, were performed in the Physical Laboratory of the University 

 of Glasgow, and had for their object the finding of the difference 

 between specimens of iron and of steel with respect to the intensities 

 of their total and residual magnetisation due to different degrees of 

 magnetising force. 



The specimens consisted of (1) wires of "soft Scotch " iron, of 

 " common wire," of " charcoal iron," and of " soft steel ;" and (2) bars 

 of cast iron and of malleable iron. The wires were 31 cm. long and 

 0*5 cm. in diameter, and weighed respectively 39*85, 39*9, 41*5, and 

 38"5 grams. The bars, two of which were of cast iron procured from 

 different foundries, were 15'25 cm. long, and of section 1 cm. square. 

 The cast iron bars weighed each 114 grams, and the malleable iron bar 

 125 grams. 



The arrangement of the apparatus employed in the investigation is 

 shown in the accompanying diagram (fig. 1). The magnetising coil, 



Fig. 1. 



represented at C, was 40 cm. in length, and consisted of three layers 

 of 600 turns each of silk-covered copper wire, wound on a brass tube 

 of the same internal diameter as the wires. It was placed on a con- 

 venient stand with its axis horizontal and at right angles to the mag- 

 netic meridian. For the experiments on the bars the coil was 21 cm. 

 in length, and consisted of five layers of 155 turns each of insulated 



