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might have occaſioned the Earth to tremble. Nor can we this Way account for that remarkable Particular attending theſe Lights, of being always ſeen on the Northſide of the Horizon, and never to the South.
Wherefore laying aſide all hopes of being able to explain theſe Things by the ordinary Vapours or Exhalations of the Earth or Waters, we are forced to have recourſe to other ſorts of Effuvia of a much more ſubtile Nature, and which perhaps may ſeem more adapted to bring about thoſe wonderful and ſurprizingly quick Motions we have ſeen. Such are the Magnetical Effuvia, whofs Atoms freely permeate the Pores of the moſt ſolid Bodies, meeting with no Obſtacle from the Interpoſition of Glaſs or Marble or even Gold it ſelf. Theſe by a perpetual Efflux do, ſome of them, ariſe from the Parts near the Poles of the Magnet, whilſt others of the like Kind of Atoms, but with a contrary Tendency, enter in at the ſame parts of the Stone, through which they freely paſs; and by a kind of Circulation ſurround it on all Sides, as with an Atmoſphere, to the Diſtance of ſome Diameters of the Body. This thing des Cartes has endeavoured to explain (Princip. Philoſoph. Lib IV.) by the Hypotheſis of the Circulation of certain skrewed or ſtriate Particles, adapted to the Pores they are to enters
But without enquiring how ſufficient the Carteſian Hypotheſis may be for anſwering the ſeveral Phænomena of the Magnet: that the Fact may be the better comprehended, we ſhall endeavour to exhibit the manner of the Circulation of the Atoms concerned therein, as they are expoſed to view, by placing the Poles of a Terreila or Spherical Magnet on a Plane, as the Globe on the Horizon of a Right Sphere: Then threwing fine Steel duſt or Filings very thin on the Plain all round it, the Particles of Steel, upon a continued gentle knocking on the underſide of the Plain, will by degrees conform themſelvesto
