112 Mr. H. Tomlinson on Thermal Conductivity [Feb. 21, 



AB was 2 inches long and CD 1 inch. 



The piece AB was also soldered to another piece of brass AE, having 

 a section \ inch square, and length about 12 inches. 



The whole was placed inside a wooden box, 2 feet long, 1 foot wide, 

 and 2 feet high, lined on the outside with tinfoil. 



AE passed through a circular hole, 2 inches in diameter, in the 

 middle of one end of the box, and through two corresponding circular 

 holes in a double screen of sheet tin, and thence into one of the 

 square apertures of one of the Leslie's cubes. The electro-magnet was 

 placed underneath BC, and two pieces of soft iron, about 3 J inches in 

 length, \ inch in breadth, and about 2 millimetres in thickness, were 

 placed on the ends of the soft iron cores, so as to be on the same level 

 with BC, and distant from B and C about 2 millimetres, the pieces 

 of iron being separated from the cores by a piece of white paper. In 

 some experiments the pieces of iron thus used were carefully secured 

 to the electro- magnet by elastic straps, and, in others, by weights 

 placed on them. A preliminary experiment, made with the strongest 

 current that was ultimately used with the electro -magnet, showed that 

 neither were the iron pieces on the cores appreciably shifted on 

 magnetising the coil, nor was the heat radiated from the coil sufficient 

 to produce any effect on one of the Gr. S. elements fastened by elastic 

 bands to the back of CD. The other Gr. S. element was in this case 

 buried in sawdust, with which the box was now filled, so as to cover 

 completely the bars and electro magnet. The sawdust also filled the 

 space between AB and CD, and the small portion of the brass bar AE, 

 which was between the box and the Leslie cube, was covered with 

 caoutchouc and cotton wool. 



The lid of the box was now put on, and some time allowed to elapse 

 until the light remained steady on the scale. 



Boiling water was then put into the cube, and a burner placed 

 underneath. Yery shortly the light began to move across the scale, 

 showing that the heat had been conducted along the compound bar to 

 the thermo element, and then the number of divisions on the scale 

 passed over by the light was taken for each minute. The adjusting 

 magnet of the galvanometer had in these and similar experiments to 

 be placed very low down in order that the number of divisions of the 

 scale passed over might not exceed 60 per minute. When the light 

 reached one end of the scale the adjusting magnet was used to bring 

 it back again to the other. In these and similar experiments it was 

 found that, after some time, either the number of divisions passed over 

 per minute increased or diminished very slowly or else remained 

 constant for some minutes. The following observations were made 

 with the specimen in question, the light being near one end of the 

 scale. The number of divisions passed over in consecutive minutes 

 was as follows (the magnetising current will be called M. C.) : — 



