OP ARTS AND SCIENCES. 211 



to the frictional generation of heat in the magnetic coil. Several 

 otiier complicating causes are apparent in the arrangement which 

 Maggi used. 



A year ago we made some experiments, by a rather rough method, 

 to find the effect of magnetism upon thermal conductivity, and obtained 

 decidedly negative results. The same results have been obtained 

 in the present experiments, though a much more sensitive arrange- 

 ment was employed. The following method was used. A bar of 

 soft Norway iron, 95 cm. long, 1.3 cm. wide, and 0.2 cm. in thick- 

 ness, was placed horizontally through the sides of a wooden box 

 6 cm. wide, and 25 cm. high. The top and one side of the box 

 were removed. 17 cm. from each end of the bar was soldered a 

 thick German silver wire. Each projecting arm of the bar was 

 enclosed in a glass tube 1.4 cm. in diameter. The ends of the tubes 

 were closed with cotton. The ends of the iron bar projected 

 slightly beyond the ends of the tubes, and were exposed to the air 

 of the room. One arm of the bar w'as placed between the poles 

 of a large electro-magnet, with its flat surface perpendicular to 

 the axis of the magnet. The axes of the poles were in the same 

 horizontal line, perpendicular to the bar. The tube between the 

 magnetic poles was wrapped in a piece of thick asbestos cloth, in 

 order to avoid complications arising from the generation of heat in the 

 magnetic coils. The distance between the poles was about 2.5 cm. 

 A Bunsen lamp was placed in the wooden box, and was so regulated 

 as to maintain the iron above it at a very dull cherry-red heat. The 

 German silver wires were connected with the wires of a reflectinof 

 galvanometer of six ohms resistance ; the connections were separated 

 by paper, bound together and covered with cloth. The lamp was 

 always lighted from four to five hours before any observations were 

 made. It was found that by this time the apparatus had practically 

 reached a condition of thermal equilibrium. At first the current from 

 a battery of ten Grove cells was used ; afterwards a battery of twenty- 

 six very large Bunsen cells was used. 



After the lamp had been burning for four hours, there was always a 

 permanent deflection of the galvanometer of about 12 cm. "When the 

 current was now passed through the magnets, this deflection was imme- 

 diately changed permanently. The change was found to be due to the 

 direct action of the magnet upon the galvanometer needle, though the 

 distance between the two pieces of apparatus was about 10 meters. 

 This deflection amounted to 2.8 cm. when the stronirer current was 

 used. Thirty minutes after the magnet was made, the galvanometer 



