To Thomas Jefferson esquire, President of the United States; the friend of science, and patron of Liberty; his obedient fellow-citizen presumes to present this Theory of Magnetism.

The polarity, deviation, and variation, of the Magnetic needle, is a subject, upon which, little light has been thrown, by those Authors, whose works have fallen under the notice of the writer of this Essay.

Dr. Halley’s Theory, of a distinct interior Globe, which seems to have been adopted by Nicholson, and submitted to, by Robertson and Blount; appears contrary to the known laws of gravitation, by which all solid bodies are drawn to the Center; and irreconcilable with the different directions and quantities of Variation in diffirent regions of the Globe. The flatness of the poles, and globular figure of the Earth, prove, that it began its rotary, or diurnal motion, before it was reduced to that solid state, in which it now exists.

While therefore, the vast chaotic Mass, was rolling and gravitating, the most ponderous parts, as Gold, and Iron-ore, would by the laws of motion and gravity, settle in the Center, and the line of the Axis; forming a mighty Cylinder through the Globe, the ends of which would be most exposed, and the sides, coated to a greater or less depth, with lighter substances.

Had the Globe settled in this uniform manner, it is probable that every bar of Iron or Steel, whose ends had been determined by natural or artificial means, to the poles of the great Natural magnet; would truly point out the Meridian of the place over which it might be suspended.

But when a bed was sunk for the Ocean, and those enormous Ridges heaved, from which the Rivers flow, this Polarity, arising from the regular construction of the Globe, would be deranged; and the smaller Magnets, would thenceforth deviate, in a greater or less degree, from the true Meridian, according to this irregular distribution of magnetic matter.

Had no subsiquent change taken place, this deviation would be the same at all times, in the same places; but by the action of Water, and the labour of Man, combined perhaps, with other causes; vast changes have taken place in and on the various parts of the Globe.

If the smaller portions of Iron-ore, so frequently seen in streams of water, may be supposed to have been for ages, sliding down the numerous Rivers of the European, and American Continents; and by the circular tide of the great Atlantic and German Oceans, deposited in the deepest part of the Northern Atlantic: and if the labour of Man, drawing vast quantities of Iron from each Continent, for marine, warlike, and domestic purposes, should be considered; it might be reasonably expected, that the artificial magnet, would have a Variation, correspondent in quantity and direction, to this progressive change.

How well this Theory may be found to agree with the original easterly deviation, and long observed westerly Variation in Europe, especially in England;—with the Original westerly deviation, and present well known easterly variation in North America;—with the rugged and rocky appearance of the polar and northern regions; and the sandy surface and golden ore of the Torrid Zone; and with the other appearances of Nature in general, and Magnetism in particular; is respectfully submitted to the consideration of those, who possess means of more extensive information.