11 A IN. 



which the clouds are Ipread, and with which die rain falls, 

 he thought, were evidences of an nniform caiile like that 

 of elettricity. The intenfity alio of electricity in his ap- 

 paratus generally correfponded very nearly to the (juan- 

 tity of rain that fell in the fame time. Sometimes all the 

 phenomena of thunder, lightning, hail, rain, fnow, and 

 wind have been obfcrved at one time ; which Ihews the 

 connedion they all have with fomc common caufe. Signior 

 Beccaria, therefore, fuppofes, that, previous to rain, a 

 quantity of eleftric matter efcapes out of the earth, m 

 fome place where there was a redundancy of it ; and in 

 its afcent to the higher regions of the air, coUefta and con- 

 dufts into its path a great quantity of vapours. The fame 

 caufe that collects, will condcnfe them more and more ; 

 till, in the places of the neareft intervals, they come ahnoll 

 into contaft, fo as to form fmall drops ; whicli, uniting 

 with others as they fall, come down in rain. The rain will 

 be heavier in proportion as the elafticity is more vigorous, 

 and the cloud approaches more nearly to a thunder- 

 cloud. He imitated the appearance of clouds that 'bring 

 rain, by infulating himfelf between the rubber and con- 

 dnttor of his electrical machine ; and with one hand 

 dropping colophonia into a fpoon fattened to the conductor, 

 and holdnig a burning coal, while his other hand commu- 

 nicated with the rubber. In thefe circumltances tlie finoke 

 fpread along his arm, and, by degrees, all over his body, 

 till it came to the other hand that communicated witli the 

 rubber. The lower furface of this fmoke was every where 

 parallel to his clothes, and the upper furface was fwelled 

 and arched hke clouds replete with thunder and rain. In 

 this manner, he fuppofes, the clouds that bring rain diffufe 

 themfelves from over thofe parts of the earth which abound 

 with eledtric fire, to thofe parts that are exhaulted of it ; 

 and by letting fall their rain, rellore the equihbrium between 

 them. Signior Beccaria alfo thought, that the elettricity 

 communicated to the air, which both receives and parts 

 with it flowly, would account for the retention of vapours 

 m a clear iky ; for fmall disjointed clouds, not difperfed 

 into rain ; for the fmaller and lighter clouds in the higher 

 regions of the air, whicli are but little affected by elec- 

 tricity ; and alio for the darker, heavy, and duggiih clouds 

 in the lower regions, which retain more of it. He even 

 imagined that fome alteration in the weight of the air might 

 be made by this eleftricity of it : the phenomena of rain, 

 he thought, favoured tlie fuppofition, that the elcftric 

 matter in the air did, in fome meafure, leflen its preffure : 

 for when the eleftric matter is aftually in the air, collecting 

 and condenfing the vapours, the barometer is lowed. When 

 the communication is made between the earth and the 

 clouds by the rain, the quickfilver begins to rife ; the 

 eleftric matter, which fupported part of the prelTure, being 

 difcharged. Lettere dell Elettricifmo. Prieftley's Hift. 

 &c. of Elcftricity, vol. i. p. 427, &c. 8vo. 



Dr. James Hutton's theory of rain is Hated and amply 

 illuftrated in the ill volume of the Edinburgh Tranfaftions, 

 p. 47, &c. It is well known that atmofpheric air is capable, 

 with a certain degree of heat, of difl'olving a given quantity 

 of water. (See Vapour.) Dr. Hutton afcertains the 

 ratio of the diffolving power of air, in relation to water, 

 with different degrees of heat ; and thus, by mixing a por- 

 tion of tranfpareiit humid warm air with a portion of 

 cold air, the mixture becomes opaque, and part of the 

 water will be precipitated ; or, in other words, the va- 

 pour will be condenfed into rain. Hence he obferves, that 

 iince the capacity of air for moilture increafes fafter than the 

 temperature, there mult be a depofition of moifture when 

 two faturated portions of air at different temperatures are 



mixed. Dr. Hutton fuppoles that heat and folutioii do not 

 increafe by equal increments; but that, in reality, if heat 



be fuppofed to increafe by equal increments ahmg a (Iraigiit 

 line, lolution will be expreffed by ordinates to a curve, 

 whofe ctmvex lide is turned towards that line. That the 

 power of folution is not increafed in the fame ratio witii 

 heat is, however, hypothetical, except when we rife pretty 

 high in the fcale, when its proportional increafe is fome- 

 what doubtful ; nor has our author fupported it by expe- 

 riment. The condenfation of the breath in air is not to 

 the purpofe, unlefs we fiippofe the air to be already fatu- 

 rated with vapour. In any view, it can only amount to 

 this, that to render it viiible, the heat mull be diminifhed in 

 a greater proportion than can be compenfated by the power 

 of folution in the body of air, in which the pclrticm expired 

 is at tirll immerfed. In order to explain the origin of rain 

 from this caufe, we mult always fuppofe a conitant dimi- 

 nution of heat to take place at the moment of the conden- 

 fation of the vapour ; but we actually find, that the change 

 from a ilate of vapour to the fluid Hate is attended with 

 heat ; fo that rain muft at once oppofe its own caufe, and 

 continued rains would be impoflible without the aid of other 

 cauies. Dr. Hutton endeavours, from his own fyftem, to 

 explain the regular and irregular fealons of rain, with regard 

 eitiier to the generality of its appearance, or the regularity 

 of its return. And to obviate the apparent exceptions of 

 tlie tlieory, from the generality of rain, he explains the pro- 

 portional quantities of rain, and adds a comparative eflimate 

 of chmates, in relation to rain with the meteorological ob- 

 fervations made in our own climate. As our limits will not 

 allow our doing full juftice to our author's reafoning, we muft 

 refer to his own paper on the fubject. 



Mr. Dalton, in his " Meteorological ElFays," (Eff. vi.) 

 expreffes his approbation of Dr. Hutton's theorj' in 

 general ; to this purpofe, he fays, " the principles of none 

 appear to me to be more plaufible and confiftent with 

 fafts." Dr. Hutton, as we have above (hewn, confiders 

 the varieties of heat and cold, affefting the folvent power 

 of the atmofphere, as the fole caufes of rain ; and Mr. 

 Dalton obferves, when we confider that evaporation and 

 the precipitation of vapour are diametrically oppofite, it 

 ia realbnable to fuppofe that they fhould be promoted 

 by oppofite caufes : and as heat and dry air are favour- 

 able to evaporation, fo cold, operating upon air replete 

 with vapour, promotes its precipitation. Dr. Hutton, 

 however, feems to confider water as chemically com- 

 bined with the atmofphere, and that cold produces preci- 

 pitation in a manner limilar to what it does in water fatu- 

 rated with fait, or in other chemical procefles ; whereas 

 Mr. Dalton fuppofes, that a portion ot the vapour, con- 

 fidered as a diftinCt and peculiar fluid, is condenfed into 

 water by cold ; but the effects refulting from the two 

 theories will be the fame. See METEOROLeGY, and Va- 

 pour. 



M. de Luc, in the 2d volume of his " Thoughts on 

 Meteorology," has direCt:ed particular attention to the 

 various circumltances that attend rain. He has alfo exa- 

 mined the feveral hypothefes of different authors, and 

 concludes, that they are altogether infufficient to ac- 

 count for the formation of it. In this inquiry the 

 grand queftion under difcullion is, what becomes of the 

 water that rifes in vapour into the atmofphere ? or what 

 is the Itate in which it fubfiils there, between the time 

 ef Its evaporation, and its faUing down in rain ? If it 

 continues in the ftate of watery vapour, or fuch as is 

 the immediate produdt of evaporation, it mull poffefs 

 the dillinttive characters effential to that fluid j it muft 



make 



