^6 Conjiderations on Dr. Huttori's Theory of Rain. 



" The caufe of rairij though often exerted, will not al- 

 ways produce the full efle6l ; a fcantv condenfation of aque- 

 ous vapour prrduces mijls on the earth, and clouds in the at- 

 iiiofphere above : and taking the gradation from one extreme 

 of tranfparent atmofphere to the other of the denfeft cloud, 

 from the fa'.hng of the gentleft mift to the heavieft rain, hail, 

 and Inow, we have an indefinite variety of appearances, all 

 flowing from one fimple principle." 



On the vifible fteam produced by the breath of animals 

 and by heated water, in a cold atmofphere, the author re- 

 marks that this appearance is not the eH'cft of the genuine 

 principles of heat and cold ; that, to explain it, the know- 

 ledge of a particular law is requifite ; and that the effefts of 

 heat and cold, in relation to air and vapour, are not uniform. 

 The law alluded to is thus laid down : 



" The difiolving power of air on water may vary in dif- 

 ferent proportions to the heat. The folution may vary as the 

 heat, or in a greater or lefs ratio, i. e. the increments of 

 each may be conflant, or, thofc of the heat being conftant, 

 the increments of the folution may be accelerated or re- 

 tarded. 



" This may be reprefented geometrically (fee fig. 7, 

 Plate III). Let CH reprefent the fcale of the thermometer; 

 a m b r, perpendicular ordinate^, the quantity of water held 

 in folution by a given quantity of air of the. temperatures 

 a and h. Join mr, and draw the curves mgr, mdr: then 

 it is evident that the ordinates to nir mark a folution varying 

 as the heat; the ordinates to mdr a folution varying in a 

 greater ratio, and to 7ngr in a lefs ratio than the heat. 



" The ordinates to line mr, drawn from a point denoting 

 the temperature of the mixture, reprefent the quantity of 

 water contained (diflblved or not) in a unit of the mixture; 

 for the ordinates m ar b are as the quantities contained in a 

 unit of air of temperatures a and /; ; and as upon mixture 

 the heat and water are uniformly diflblved (difi'ufcd ?), they 

 vary in the fame proportion, and may be expreil'cd l&y the 

 fame mcafure. 



'' Suppofing equable folution, mix equal portions of fatu- 

 rated air, temperatures 10 and 40; the mixture of tempe- 

 rature 25 is reprefented by op, which alio rcprcfents the 

 quantity of water in a unit of the mixture, and the quan- 

 tity held in folution by a unit of air at temperature 25. 



" So two portions of tcniperature 40, being mixed with 

 one of temperature 10, the temperature produced 30 will be 

 exprefled by uq. 



*' lit the curve mdr let equal portions of the folution at 

 6 40 



