Note w — BOOK V.
Reading edition
Dr. Gilbert, the most learned and accurate Writer on the Magnet, shews, that its Attractive Virtue was known as early as Plato and Aristotle: but its Direction was a Discovery of later Ages. He saith, Superiori ævo 300 aut 400 labentibus annis, Motus Magneticus in Boream & Austrum repertus, aut ab hominibus rursus recognitus fuit. De Mag. L. 1. c. 1. But who the happy Inventer of this lucky Discovery was, is not known. There is some, not inconsiderable, Reason, to think our famous Country-man, Rog. Bacon, either discovered, or at least knew of it. But for its Use in Navigation, Dr. Gilbert saith, in regno Neapolitano Melphitani omnium primi (utì ferunt) pyxidem instruebant nauticam.——edocti à cive quodam Jol. Goia A. D. 1300. ibid. If the Reader hath a mind to see the Arguments for the Invention, being as old as Solomon’s or Plautus’s Time, or of much younger Date, he may consult Hakewill. ib. c. 10. §. 4. or Purchas Pilgr. L. 1. c. 1. §. 1.
As to the Magnetick Variation, Dr. Gilbert attributes the Discovery of it to Sebastian Cabott. And the Inclination, or Dipping of the Needle, was the Discovery of our ingenious Rob. Norman. And lastly, The Variation of the Variation was first found out by the ingenious Mr. H. Gellibrand. Astr. Prof. of Gresham-Col. about 1634. Vid. Gellibr. Disc. Math. on the Variat. of the Mag. Need. and its Variat. Anno 1635.
But since that, the before commended Dr. Halley, having formerly, in Philos. Trans. Nᵒ. 148, and 195, given a probable Hypothesis of the Variation of the Compass, did in the Year 1700, undertake a long and hazardous Voyage, as far as the Ice near the South Pole, in order to examine his said Hypothesis, and to make a System of the Magnetical Variations: Which being soon after published, has been since abundantly confirmed by the French, as may be seen in several of the late Memoirs de Physique & de Mathematique, publish’d by the French Academie des Sciences.
To these Discoveries, I hope the Reader will excuse me, if I add one of my own, which I deduced some Years ago, from some magnetical Experiments and Observations I made; which Discovery I also acquainted our Royal Society with some time since, viz. That as the common, horizontal Needle is continually varying up and down, towards the E. and W. so is the Dipping-Needle varying up and down, towards or fromwards the Zenith, with its Magnetick Tendency, describing a Circle round the Pole of the World, as I conceive, or some other Point. So that if we could procure a Needle so nicely made, as to point exactly according to its Magnetick Direction, it would, in some certain Number of Years, describe a Circle, of about 13 gr. Radius round the Magnetick Poles Northerly and Southerly. This I have for several Years suspected, and have had some Reason for it too, which I mentioned three or four Years ago at a Meeting of our Royal Society, but I have not yet been so happy to procure a tolerable good Dipping-Needle, or other proper one to my Mind, to bring the Thing to sufficient Test of Experience; as in a short Time I hope to do, having lately hit upon a Contrivance that may do the Thing.