On the diamagnetic constants of bismuth and calc-spar in absolute measure

SINCE my experiments on the magnetic constants of iron, nickel and cobalt, I have sought the means of determining those of some diamagnetic substances, and to that end have described a method in this Journal for May, 1875, (vol. ix, page 357). As Mr. Jacques, Fellow of the University, was willing to take up the experimental portion, I have here worked up the subject more in detail and brought the formulre into practical shape. No experiments have been made on this subject so far, but some rough comparisons with iron have been made by Becquerel, Plucker and Weber. But as iron varies so greatly, and as the methods of experiment are inexact, we cannot be said to know much about the subject. As, however, the relative results of these experiments and those of Faraday can be accepted as reasonably exact for diamagnetic substances and weak paramagnetic ones, it is only necessary to make a determination of one substance such as bismuth, and then the rest can be readily found. But as bismuth is very crystalline it is necessary to make our formulre general, unless we use bismuth in a powder, which would introduce errol'. The general method of experiment has been indicated in the paper before referred to, but I may here state that it consists in counting the number of vibrations made by a bar hung in the usual manner between the poles of an electromagnet. The distribution of the magnetic force in the field being known, we can then calculate the force acting on the body, and the comparison of this with the time of vibration gives us the means of determining the constant sought. But I will leave the more exact description to be given by Mr. Jacques in the experimental part. Explomtion of .field.