On the changes produced by magnetisation in the length of rods of iron, steel, and nickel

Abstract

The earliest systematic experiments on the effects produced by magnetisation upon the length of iron and steel rods were those of Joule, an account of which is published in the “Phil. Mag.” of 1847. The experiments were made with bars 36 inches long, which were placed inside a solenoid 38 inches long; and the variations in the length of the bars when currents of electricity were passed through the solenoid were measured by means of a delicate micrometer, each division of which indicated a change of 1/138528 inch. Using bars of iron and soft steel, he found that their length was increased by magnetisation, the elongation varying up to a certain point as the square of the intensity of the magnetisation, temporary or permanent, of the bar, and he remarked that the elongation was, for the same magnetisation, greater in proportion to the softness of the metal.