222 PHILOSOPHICAL TRANSACTIONS. [aNNO I716. 



the poles of a terrella or spherical magnet on a plane, as the globe on the hori- 

 zon of a right sphere : then strewing fine steel dust, or filings, very thin on 

 the plain all round it, the particles of steel, on a continued gentle knocking on 

 the underside of the plain, will by degrees conform themselves to the figures 

 in which the circulation is performed. Thus, in fig. 2, pi. 5, let abcd be a 

 terrella, with its poles a the south, and b the north; and by doing as prescribed, 

 it will be found that the filings will lie in a right line perpendicular to the 

 surface of the ball, when in the line of the magnetical axis continued. But 

 for about 45 degrees on either side, from b to g or i, and from a to h or k, 

 they form themselves into curves, more and more crooked as they are remoter 

 from the poles ; and more and more oblique to the surface of the stone : as 

 the figure truly represents, and as may readily be shown by the terrella and 

 apparatus for that purpose, in the repository of the Royal Society. Hence it 

 may appear how this exceedingly subtle matter revolves; and particularly how it 

 permeates the magnet with more force and in greater quantity in the circum- 

 polar parts, entering into it on the one side, and emerging from it on the 

 other, under the same oblique angles: while in the middle zone, about c and 

 D, near the magnet's equator, very few if any of these particles impinge, and 

 those very obliquely. 



Now by many and very evident arguments it appears, that our globe of earth 

 is no other than one great magnet, or, if I may be allowed to allege an inven- 

 tion of my own, rather two ; the one including the other as the shell includes 

 the kernel ; for so and not otherwise we may explain the changes of the varia- 

 tion of the magnetical needle : but to our present purpose the result is the 

 same. It suffices, that we may suppose the same sort of circulation of such 

 an exceedingly fine matter to be perpetually performed in the earth, as we observe 

 in the terella ; which subtle matter freely pervading the pores of the earth, and 

 entering into it near its southern pole, may pass out again into the ether, at 

 the same distance from the northern, and with a like force ; its direction being 

 still more and more oblique, as the distance from the poles is greater. To this 

 we beg leave to suppose, that this subtle matter, no otherwise discovering itself 

 but by its effects on the magnetic needle, wholly imperceptible, and at other 

 times invisible, may now and then, by the concourse of several causes very 

 rarely coincident, and to us as yet unknown, be capable of producing a small 

 degree of light ; perhaps from the greater density of the matter, or the greater 

 velocity of its motion : after the same manner as we see the effluvia of electric 

 bodies, by a strong and quick friction, emit light in the dark : to which sort of 

 light this seems to have a great affinity. 



This being allowed, I think we may readily assign a cause for several of the 



