1878.] Mr. H. Tomlfnson on Thermal Conductivity of Iron. 109 



February 21, 1878. 



Sir JOSEPH HOOKER, K.C.S.L, President, in the Chair. 



The Presents received were laid on the table, and thanks ordered 

 for them. 



The following papers were read : — 



L " On the Alteration of the Thermal Conductivity of Iron 

 and Steel caused by Magnetism." By Herbert Tomlin- 

 SON, B.A., Demonstrator of Natural Philosophy, King's 

 College, London. Communicated by Professor Stokes, 

 Sec. Roy. Soc. Received December 17, 1877, 



The writer has, for several months, been engaged in experimenting 

 on the alteration of the electrical and thermal conductivity of iron 

 and steel, produced by magnetism, with the intention of determining 

 such alteration in absolute measure. But as, before the complete 

 determination of the data sufficient for the purpose, a considerable 

 time must elapse, he would venture to offer to the Society, in a pre- 

 liminary note, some results which have already been obtained by him. 



In these experiments, the apparatus chiefly employed to impart 

 magnetism consisted of an electro-magnet, with soft iron cores, 1 inch 

 in diameter and 5 inches in length, surrounded by cotton-covered 

 copper wire, T Vth of an inch in diameter, having a resistance of nearly 

 1 ohm, and a coil constructed as follows: — a thin tube of polished 

 tin, 1^ inch internal diameter and 4^ inches long, was covered with 

 vulcanised caoutchouc to a depth of T V^h of an inch, and on this 

 was wound 3 lbs. of cotton-covered copper wire, ¥ ^th of an inch 

 diameter, followed by 3 lbs. of wire, -^th of an inch in diameter. 

 Inside the first tube was placed a second, 1 inch internal diameter, con- 

 nected by ebonite with the first at the two ends, the second tube being 

 concentric with the first, and of the same length, so that, between the 

 inner tube and the outer, should be interposed a layer of air nearly 

 ith of an inch in thickness. This arrangement was employed to pre- 

 vent the heat from the magnetising coil reaching the bars placed 

 inside ; also, to prevent ingress or egress of heat ; the bars used with 

 the coil were covered with vulcanised caoutchouc, so that they lay 

 with their axes coinciding with the axis of the coil. 



To measure the heat conducted along the bars two sets of thermo- 

 elements were constructed. The first was made up of two small 

 strips of copper, J inch long and J inch broad, of small thickness. To 

 these was soldered about 1 foot of silk-covered german-silver wire 

 Y^th of an inch in diameter, the copper strips being also connected 



