224 DISSERTJTION on tk 



fphere, is not conftant, but I think follows a fort of cloudinefs, 

 which occafionally takes place on a change of temperature, as 

 if it was going to fnow ; but on the cold increafing a few de- 

 grees, which it does often very fuddenly, the Iky becomes in- 

 ftantly clear again, and feems to have acquired the little parti- 

 cles in quefliion, which I have often thought I felt a(5ling againfk 

 my face, while driving with great velocity in a fledge. 



That I may feparate as much as poflible theory from fads, 

 I referve to this place fome explanation of what I have faid 

 above, and beg leave to hazard a conjedlure, in form of a 

 query, for thofe who have more leifure and genius than myfelf. 

 It would indeed be difficult to reconcile the idea of our atmo- 

 fphere pofleffing a greater quantity of eledric fluid in winter 

 than fummer, with the difcoveries of Meflrs de Volta and 

 Saussure, who have found the eleflricity of the air in dry 

 weather to be confliantly pofitive. The lafl: mentioned gentle- 

 man fuppofes its pofitive ftate to be maintained by a regular 

 fupply of vapours from the earth, (which are difcovered to 

 abound with that fluid) carrying up a portion of the eledricity 

 that belongs to the globe. Now, as in the north the earth is 

 hard frozen during winter, one fliould think the fupply by eva- 

 poration cannot be fo great in this feafon as in fummer, and 

 of courfe its pofitive ftate with difficulty kept up from this 

 fource, according to Dr Franklin's Theory of Plus and Mi- 

 nus. Will that of two diftindt fluids (to which Mr Saussure 

 feems to lean in fome part of his works) account for it better ? 

 There is a theory very prevalent in Germany and Sweden ; nay, 

 we even find the refped^able names of Bergman, Scheele, 

 WiLKE, i^c. amongfl: its advocates. This is a fufficient reafon 

 for my giving it a place in this paper, left it fliould not be ge- 

 nerally known in Britain. 



Positive eledricity is fuppofed to be common air faturated 

 with heat or fire, as they term it ; negative eledlricity is fup- 

 pofed to be phlogifton, combined with an acid. As to the 



commotion, 



