310 PHILOSOPHICAL TRANSACTIONS. [aNNO 1772. 



XVUl. Observations on Atmospherical Electricity ; in Regard to Fogs, Mists, 



i^c. By Thomas Ronayne, Esq. With some Remarks by Mr. tVm. Henley. 



p. 137. 



Some years ago Mr. R. discovered, by Mr. Canton's electrometer, described 

 in the Phil. Trans., vol. 48, that the air of Ireland is, during the winter season, 

 in almost a constant state of positive electricity ; which however is so weak, that 

 in order to observe it satisfactorily, he always found it necessary to have the cork 

 balls suspended from threads of a middling fineness, 6 or 7 inches in length, 

 (juite straight, and to avoid as much as possible any interruption from the wind. 



He also had frequent recourse to the following contrivance, by which he was 

 enabled, within doors, to pursue his inquiries with greater accuracy and advan- 

 tage : having procured a slender tapering piece of woo<l, about 5 feet long, to 

 the smaller end of which an electrometer was affixed, by means of a small hook ; 

 he placed it out from an open garret window, and fastened the other end with a 

 small hasp to one of the jambs : he had also at hand another piece of wood, in 

 the ends of which, a small glass tube and a stick of sealing wax had been inserted. 

 Either of these was occasionally excited, and applied near the cork balls, to de- 

 termine more precisely the kind of electricity with which they might happen to 

 be affected , and he was always careful in making his experiments on that side of 

 the house where the wind had least power. 



He found the air in winter, at a proper distance from buildings, trees, masts 

 of ships, &c. very sensibly electrified, during a frosty or foggy state of the wea- 

 ther ; and in mists too, but in a less degree : he also discovered small signs of it 

 in calm and cloudy weather. The air in summer never showed any sign of elec- 

 tricity, except when a fog happened in the cool of the evening, or at night ; in 

 which case he always discovered manifest marks of electricity, sensibly weaker 

 than those observed in winter-fogs, but precisely of the same kind, that is, po- 

 sitive. He often examined the state of the air at the time of an aurora borealis, 

 and could not discover any indication of electricity, except when a fog had ap- 

 peared at the same time; in which case, the electricity has been, in every respect, 

 the same as that of a fog at any other time. Once indeed, during an aurora 

 borealis on a remarkable serene night, he discovered some signs of a very weak 

 positive electricity. 



As the electricity of the air is generally positive, he never knew an exception 

 but one, which presented itself during a fog on a winter day, that proved uncom- 

 monly warm), is it not reasonable to believe, that cold electrifies the atmosphere 

 positively? and if so, may not one be led to imagine, that heat electrifies 

 it negatively? But this he only offers as a conjecture, not being able to 

 advance any thing decisive on the subject, and knowing that one sort of electri- 

 city may often be productive of the other, as is plain from Dr. Franklin's experi- 



