I visited, the last year, the mine of magnetic iron at Succassunny, belonging to Governor Dickerson of New-Jersey. The mine had not been worked for a year past, and I did not descend it. The proprietor, a gentleman of distinguished science, informed me of a singular circumstance attending it, which was too important to be left unnoticed. The mine is worked at the depth of 100 feet; direction of the bed, northeast and southwest; inclination nearly perpendicular. The ore in the upper part of the bed is magnetic, and has polarity; but that raised from the bottom has no magnetism at first, but acquires it after it has been some time exposed to the influence of the atmosphere. This fact, of which there is no doubt, struck me as most singular. I could not recollect any similar observation; and it is only lately that I have found that Werner had observed, that iron sand, raised from the depth of 100 feet, had no magnetism. See Rees's Cyclopedia, Art. Sand. I could only account for this circumstance by supposing that magnetism existed not in the interior of the earth, as was supposed, but only on the surface, and in such bodies as received this principle from atmospheric, or celestial influence. The late discovery of the magnetic influence of the violet rays of light, by M. Morechini, a notice of which has since reached us in the journals, connected with the above fact, leads me to believe that light is the great source of magnetism. A learned foreigner,[13] whose residence in this country has contributed much to its scientific improvement, has also informed me that other substances than metallic have been found, by compression, to be magnetic. It is well known that the violet ray is the most refrangible, or has the most attraction to matter. But there are other rays, which Herschel, who some years since discovered them, calls invisible rays, which are still more refrangible, are next beyond the violet, when refracted, and partake of most of its properties, except that they are invisible. I have not yet seen any account of the experiments of M. Morechini, other than the notice in the journal; but I trust I shall soon be able to determine whether those invisible rays do not possess the magnetic power as well as the violet; or, perhaps, possess it exclusively. As the refraction of the atmosphere in the polar circles, is at least ten times greater than in the tropics, a greater quantity of the magnetic rays will there be separated and combined than elsewhere; and of course arises excess of magnetism. Hence the direction of magnetic bodies towards the northern and southern extreme regions. The great absorption and emission of light in the polar regions, by the ice and snow, may cause the extraordinary illumination of that country during the absence of the sun, and the emission of the magnetic rays with electricity may, perhaps, give us the aurora borealis.