VOL. XXIX.] PHILOSOPHICAL TRANSACTIONS. 221 



tity, nor sudden enough to shake its surface, or to open itself a passage by 

 rending it. And as these vapours are suddenly produced by the fall of water 

 on the nitro-sulphureous fire under ground, they might well be thought to get 

 from thence a tincture which might dispose them to shine in the night, and a 

 tendency contrary to that of gravity ; as we find the vapours of gunpowder, 

 when heated in vacuo, to shine in the dark, and ascend to the top of the 

 receiver though exhausted. 



Nor should I seek for any other cause than this, if in some of these in- 

 stances, and particularly this whereof we treat, the appearance had not been 

 seen over a much greater part of the earth's surface than can be thus accounted 

 for. It having in this last been visible from the west side of Ireland to the 

 confines of Russia and Poland on the east, nor do we yet know its limits on 

 that side, extending over at least 30 degrees of longitude ; and in latitude, 

 from about 50 degrees over almost all the north of Europe; and in all places 

 exhibiting at the same time the same wonderous circumstances. Now this is a 

 space much too wide to be shaken at any one time by the greatest of earth- 

 quakes, or to be afi^ected by the perspiration of that vapour, which being 

 included and wanting vent, 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 north -side of the horizon, and never 

 to the south. 



Therefore laying aside all hopes of being able to explain these things by 

 the ordinary vapours or exhalations of the earth or waters, we must have 

 recourse to other sorts of efi3.uvia of a much more subtle nature, and which 

 perhaps may seem more adapted to bring about those wonderful and sur- 

 prisingly quick motions we have seen. Such are the magnetical efiftuvia, whose 

 atoms freely permeate the pores of the most solid bodies, meeting with no 

 obstacle from the interposition of glass or marble, or even gold itself. Some 

 of these, by a perpetual efflux, 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 Descartes has endeavoured 

 to explain (Princip. Philosoph. lib. iv.) by the hypothesis of the circulation of 

 certain screwed or striate particles, adapted to the pores they are to enter. 



But without inquiring how sufficient the Cartesian hypothesis may be for 

 answering the several phaenomena of the magnet : that the fact may be the 

 better comprehended, we shall endeavour to exhibit the manner of the circu- 

 lation of the atoms concerned therein, as they are exposed to view, by placing 



