Experimental researches in electricity. Twenty-fifth series. On the magnetic and diamagnetic condition of bodies

Abstract

As the author could find no polarity in diamagnetic bodies when under magnetic influence (a result described in the 23rd Series of these Researches), he endeavoured to discover some other physical condition of them, and of magnetic bodies, by which he might obtain an insight into their respective natures, and establish the true place of the magnetic zero; and considering the power with which a magnetic body moves, or tends to move, from weaker to stronger places of action, and that of a diamagnetic body to pass from stronger to weaker places of action, he hoped to obtain some results of condensation with the first class, and of expansion with the second, when they were subjected to very strong magnetic action; the respective bodies being selected from the class of gaseous substances, in which change of volume can be easily produced and measured. In the first place, therefore, a ray of light was passed over the surface of powerful magnetic poles surrounded by different gases, and the place of its source carefully examined by telescopes, micrometers, and other means, to ascertain whether the layer of air in contact with the poles was affected in its refracting force; but though the experiment was made in oxygen, nitrogen, and other gases, not the slightest effect was visible. Resigning this process, therefore, two air-tight chambers were made, in which the magnetic poles formed the chief part of the internal surface of the chamber. The one was formed by bringing the flat ends of the two poles to within 1/60th of an inch of each other, with a frame all round to form the sides; and the other by cutting away the central parts of an iron cylinder so as to give it the form of an hour-glass, and then enclosing that part by an air-tight copper tube. Cocks were attached to these chambers for the introduction and removal of gases, and for the application of gauges, which were able to indicate a change of volume equal to the part of the contents of the chamber. When any given gas was introduced into the chamber, and the latter then placed between the poles of the electro-magnet, any possible alteration of volume would be shown by the gauge as soon as the magnet was rendered active; but whatever gas was employed, or whatever power of magnet used, not the slightest change was produced.