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chemical vcfTtl, wliereintlie matterof all tlic kinds of fuh- 

 liinary bodies is copioufly floating; and thus cxpofed to 

 the continual aclion of that imnienfe fnrnace the fun ; 

 whence proceed innumerable operations, fnhlimatlons, fe- 

 parations, compofitions, digtllions, fermentations, putre- 

 faftions, &c. 



We have a large apparatus of inftruments, contrived for 

 indicating and mearuring the Hate and alterations of the 

 atmofphere ; as Anemometers, Barometers, Eudio- 

 meters, Hygrometers, Manometers, Thermome- 

 ters, &c. 



Atmosphere, Eledrtdly of the. Befide thofe large quan- 

 tities of the eleftric matter, with which the clouds are 

 charged in a thundcr-ftorm, it has been obfen,-ed, firll by 

 RI. Monnicr in 1752, and afterwards repeatedly and vvitli 

 peculiar attention by others, particularly by the abbe 

 Mazeas in 1753, and Mr. Kinnerfley, that the atmofphere 

 is never wholly dellitute of the eleftrical fluid. A perfon 

 eledrified negatively may fatisfy himftlf of this, by ex- 

 tending his arm in the open air, and prefenting a long 

 fharp needle with its point upwards; for the cleclric mat- 

 ter colleded from the remoter air will appear luminous, 

 as it converges to the pjint of the needle. Mr. Canton's 

 balls are likewife an excellent contrivance for the fame 

 purpofe, and may be made ufe of, not only for deter- 

 mining the elefiricity of the atmofphere in general, but the 

 pofitive or negative quality of it. According to this in- 

 genious philfopher, deficcated atmofpheric air, when heated, 

 becomes negatively eleftric ; and when cooled, the electricity 

 is of the pofitive kind, even wlwn the air is not permitted 

 to expand or contraft ; and the expaiifion or contrattion of 

 atmofpheric air occafions changes in its eleftrical flate. 

 But no eleftrician, in the earlier ilage of this fcience, con- 

 dufted his obfervations in this way with greater accuracy 

 and farther purfued them, than S. Beccaria. (See " Bec- 

 caria's Eflay on Atmofpheric Eleftricity, annexed to the 

 Englifh trandation of his Artificial Eleftrity," p. 42l,&c.) 

 From him we learn, that the atmofphere difcovers no figns of 

 eleftricity in windy and clear weather, nor in moid weather 

 without rain, nor when the fl^y is covered with dillinft and 

 black clouds with a flow motion ; but he always obferved 

 a moderate, though interrupted eleftricity, for the moil 

 part of the pofitive kind, in a clear flcy, when the weather 

 was calm ; and in rainy weather without lightning, a little 

 before the rain fell, and during the continuance of it, till the 

 rain was almoll over. The eleftricity of the atmoiphere, 

 according to Beccaria, was always pofitive, during the day 

 and in dry weather, bat always negative, when a bright or 

 ferene atmofphere fucceeded dark and moill weather. The 

 q\iantity of atmofpherical eleftricity was found to increafe 

 after the rifing of the fun, and during his progrefs; and its 

 augmentation was the more confiderable, as the nioifture of 

 the air was dimiiniflied ; but it decreafed in the evening. 

 In days equally dry, the degree of eleftricity at noon 

 was proportional to the degree of heat ; and in a ferene 

 atmofphere, with little wind, a confiderable quantity of the 

 eleftrical matter commonly arofe after fun-let, during the 

 precipitation of dew. Tfiick fogs were obferved, daring 

 their afcent into dry air, to carry with them a confiderable 

 quantity of the eleftric matter. And the elcclrieity was 

 llrongcr, as his rods wer^ higher, and the ftrings, which 

 were extended and infulattd in the open air, were longer. 



Mr. Cavallo (Complete Treatife on Eleftricity. vol. ii. 

 p. 42. ed. 4.) deduces the following conclufions iioni his 

 experiments and obfervations on tins fubjeft ; viz. that there 

 is in the atmofphere at all times a quantity of ekftrie mat- 

 ter : — that the eleclricity of the atmofphere, and of fogs, 

 is always pofitive •. — that, in gener-,1, the ftrungeft tl.-ftncity 



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is obferv-able in thick fogs, and alfo in frofly weather; and 

 the weakcll, when it is cloudy and warm, and rain approach- 

 es : — that it does not fcem to be Icfs by night than in the 

 day: — and that the electricity is ftronger in places more 

 elevated than in thofe that are lower; and therefore, accord- 

 ing to this rule, if it may be extended to any dirtancc 

 from the earth, the eleftricity in the higher regions of the 

 atmofphere mud be exceedingly ftrong. Mr. Read, in h!» 

 " Summary View of the Spontaneous Eleftricity of the 

 Earth and Atmofjjherc," obferves, that the eleftricity of 

 the atmofphere in moderate iveathcr, was always found to 

 be pofitive ; in ftorms and diflurbed dates of the air, fre- 

 quently negative ; and fuddenly and repeatedly changing 

 from one llate to the other. Warm fmall rain was found 

 to be very llightly eleftric ; large drops, ftrongly ; hail 

 fliowers, the mod intenfely of all. Jn an eaderiy wind 

 of long continuance, and reckoned unhealth.ful, the eleftri- 

 city was lo faint, as to refi'iire the niceft of all known 

 teds for difcovcring its cxirtence. The vapour of water, 

 as fuun as it had attained the height of five or fix inches of 

 infulation in the air, was found to be perma:>ently and 

 pofitivtly electrified; and the fiirface from which it evapo- 

 rated, negatively. Vapour has a greater capacity for 

 eleftricity, or abfurbs and requires more of th.is fluid, than 

 water in its denfe llate ; and therefore rarefaftion mull 

 diminifli, and condenfation increafe, the fenfible eleftric 

 charge of the vapour. Hence, in ferene weather, the at- 

 mofpliere is fubjeft to a regular flux and reflux, or increafe 

 and diminution of eleftricity, twice in every twenty-four 

 hours, depending on the aftion of the fun, and the cor.fc- 

 quent evaporation and date of the vapours. This diligent 

 obferver and judicious reafoner further obferves, thit a 

 limited portion of the cartli's furface is often fenfibly elec- 

 trified ; over It, there is always a proportionate quantity of 

 the contrary eleftricity in the atmofphere ; and when an 

 eleftrified cloud is carried forward by wind, an equal and 

 oppofite eleftric charge keeps pace with it on the earth, 

 till the two charges, becoming more augmented, or ap- 

 proaching nearer to one another, or meeting with fome 

 condufting eminence, rufli together, and produce an es- 

 plofion. 



The fubjeft of atmofpherical eleftricity has engaged the 

 particular attention of M. Saulfure ; aVid few perfona have 

 had more favourable opportunities for obfcr\-ing the pheno- 

 mena that attend it, or pofleded a more extenfive ac- 

 quaintance with meteorology in general, for enabling him to 

 illudrate thefe phenomena by appofite obfervations, than 

 this author. He confirms tlie faft noticed by others, and 

 previoufly known, that aerial eleftricity varijs according to 

 the fitu^tion, being generally llronged in elevated and infu- 

 lated lituations, and not obfervable under trees, in dreets, 

 houfcs, or inclofed places. But it is not fo much the 

 height, as the fituation of the places, which determines the 

 degree of eleftricity : for the projecting angle of a high 

 hill will often exhibit a drongcr eleftricity than the plain 

 at the top of the hill, as there arc fewer points in the former 

 to deprive the air of its eleftricity. I'lie iiitenfity of tiie 

 atmofpherical electricity is fubjeft to a great varitiy of 

 changes, of which fome depend on obvious circuin dance* 

 and others are altogether inexplicable. Thefe changes, 

 according to M. Saulfure, were fometimes fo lapid ia their 

 iucctflion, that he liad not lime to note them down, \\nien 

 niiu I'alls without a Iljrm, thefe changes are rot \o fuddcn ; 

 but with refpeft to the inttnfity of the eleftric force, they 

 are very irregular ; wliilfl the quality of it is more conftant. 

 Rain or fnow almod always gives pofitive cleftricitv. lu 

 cloudy weather, without rains or dorms, the clecfricitT 

 generally follows the fame laws as in ferene weather. Itt 



iuteofity 



