Page:A history of the theories of aether and electricity. Whittacker E.T. (1910).pdf/75

 have mention'd any thing relating to this property of the Magnet, have agreed, not only that the Attraction and Repulsion of Magnets are not equal to each other, but that also, they do not observe the same rule of increase and decrease."

"The Attraction and Repulsion of Magnets decreases, as the Squares of the distances from the respective poles increase."

This great discovery, which is the basis of the mathematical theory of Magnetism, was deduced partly from his own obscrvations, and partly from those of previous investigators (e.g. Dr. Brook Taylor and P. ), who, as he observes, had made accurate experiments, but had failed to take into account all the considerations necessary for a sound theoretical discussion of them,

After Michell the law of the inverse square was maintained by Tobias Mayer of Göttingen (b. 1723, d. 1762), better known as the author of Lunar Tables which were long in use; and by the celebrated mathematician, Johann Heinrich Lambert (b. 1728, d. 1777)

The promulgation of the one-fluid theory of electricity, in the middle of the eighteenth century, naturally led to attempts to construct a similar theory of magnetism; this was effected in 1759 by Aepinus, who supposed the "poles" to be places at which a magnetic fluid was present in amount exceeding or falling short of the normal quantity. The permanence of magnets was accounted for by supposing the fluid to be entangled in their pores, so as to be with difficulty displaced. The particles of the fluid were assumed to repel each other, and to attract the particles of iron and steel; but, as Aepinus saw, in order to satisfactorily explain magnetic phenomena it was necessary to assume also a mutual repulsion among the material particles of the magnet.

Subsequently two imponderable magnetic fluids, to which