Magnetic inclination is besides subject to changes. There are also variations of magnetic force which occur at very irregular periods, and cannot be said to follow any laws. These disturbances are called Magnetic Storms, of which the Aurora Borealis is one result. Professor Faraday in his memorable experiments divided a long list of different substances into para-magnetic and dia-magnetic bodies. He classed them under these two heads, according as they took up a certain position parallel or perpendicular to the axial or equatorial line. This definition of “dia-magnetic” was “a body through which the lines of magnetic force are passing, and which does not by their action assume the usual magnetic state of iron or loadstone.” He concluded that all bodies were magnetic, and by suspending a great number of various substances he found they placed themselves axially,—that is, lying between the poles of the magnet, or equatorially,—viz., at right angles to that line. If the magnets be suspended at each side the same bodies will assume a position with their longest diameters between the poles, while others will be repelled by the magnets even if the poles be reversed. So those bodies which are attracted and lie in the axial line are termed para-magnetic; those repelled into the equatorial line are termed dia-magnetic. In the “Proceedings of the Royal Society for 1846,” Faraday’s account of the various experiments can be studied in detail. We can only give a brief _resumé_ of them here; and he showed that the motions displayed by dia-magnetic bodies in a magnetic field are all reducible to one simple law—viz., that the particles of the dia-magnetic tend to move into the positions of the weakest magnetic force. He experimented upon a large number of bodies and gases; he tested crystals, metals, liquids, and solids, and proved in whatever state a body might be in the effect was the same; whether simple or compound, it made no difference. Of course in a compound the preponderance of the dia-magnetic or para-magnetic property would influence the result, and the medium in which the body operated on was placed, was a condition in the experiment. He proved that if a body be suspended in a medium or surrounded by a medium whose power either way is stronger than the body, that body is para-magnetic or dia-magnetic, according as it is surrounded by a medium whose power is weaker or stronger than the body itself. The arrangement of the bodies is as follows, from the para-magnetic to the dia-magnetic, bismuth being the most dia-magnetic of all:— PARA-MAGNETIC METALS. Iron. Nickel. Cobalt. Manganese. Chromium. Cerium. Titanium. Palladium. Platinum. Osmium. DIA-MAGNETIC. Bismuth. Antimony. Zinc. Tin. Cadmium. Sodium. Mercury. Lead. Silver. Copper. Gold. Arsenic. Uranium. Rhodium. Iridium, etc.