I. On the alteration of the thermal conductivity of iron and steel caused by magnetism

Abstract

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 preliminary 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, 1/16th 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 1/4 inch internal diameter and inches long, was covered with vulcanised caoutchouc to a depth of 1/16th of an inch, and on this was wound 3 lbs. of cotton-covered copper wire, 1/10th of an inch diameter, followed by 3 lbs. of wire, 1/20th of an inch in diameter. Inside the first tube was placed a second, 1 inch internal diameter, connected 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 1/8th of an inch in thickness. This arrangement was employed to prevent 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.