VOL. LXII.] PHILOSOPHICAL TRANSACTIONS. 311 



inents. If cold electrifies the air positively in this climate, which seems extremely 

 probable, may it not electrify it negatively at and about the place of our anti- 

 podes ? Does not a consideration of the effects discovered in the tourmalin favour 

 this surmise ? 



The electricity of the air, in frosty, foggy, or misty weather, is not strong 

 enough to yield any spark, even by insulating a sharp pointed wire in it, which 

 however attracts very light bodies at a small distance ; while on the contrary that 

 of the clouds generally affords considerably strong sparks. When a fog becomes 

 very thick, the cork balls approach; but when it returns to its former state, they 

 open again at their first distance ; and when it rained in foggy weather, the balls 

 closed, and opened again on the fog's appearance anew, after the rain had 

 ceased : there is however a certain degree of density necessary in a fog, in order 

 that the balls might exert their greatest divergency. 



Most, if not all, fogs partake of a smell much like that of an excited glass 

 tube, and indeed so does the common air very frequently. As fogs sometimes 

 appear in a very moist state of the air, Mr. R. was for some time at a loss to ac- 

 count on what principle they could retain their electricity : but having at length 

 remarked that electrified bodies, insulated with sealing wax, preserved their 

 electricity for a tinie in very damp air, he concluded that moisture is but a very 

 slow conductor. 



Having, on the contrary, observed that bodies, insulated with dried silk, had 

 lost their electricity in a very short time, he attempted to render it a non-conduc- 

 tor, by having varnished it over with oil of turpentine, balsam of sulphur, and 

 such like, but did not succeed; for silks so treated soon became a conductor, 

 and increased considerably in weight, if the air happened not to be very dry ;* 

 so much indeed that ordinary silk, from its power of absorbing moisture from 

 the air, may well serve as an occasional hygrometer, either by being put into a 

 balance, or having an electrified body insulated with it. 



When the density of fogs, floating near the earth, increases considerably, the 

 balls always approach ; but when they are situated high in air, the reverse ge- 

 nerally happens. Mr. R. had an opportunity of remarking a struggle between 

 breezes from the n.w. and s. e. at the same time, in which the one seemed 

 sometimes to prevail, and afterwards the other. This contention was succeeded 

 by a smoky haziness, which, like a fog, occasioned the balls to open : as the 

 haziness -f- thickened, they opened wider, and still wider when it dissolved into 

 rain ; but their repelling power became greatest in proportion as the drops in- 

 creased. 



• Even glass attracts moisture to its surface, which makes it a conductor of electricity ; and conse- 

 quently not so convenient as sealing wax. — Orig. 



f An electrical body, -when contracted in its dimension, will have its electricity increased, as ap- 



