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Show EVAPORATION. N TE XXV. 10 ffibly be held in folution by the f f heric water may po 1 b . 1 the Another portion o atmo p . . t" n oft he water fecms to e ell ler 4· 1 d fl:orms a prectptta to ro 1 n :c fluid fince in t lun er '. r 1 l , nricity. But it appears more P - e eel! I ' f h d 1cbon 0 t 1e e eeL ! I h caufe or the confequence o t e e .l louds b the eduction of its heat, am t lat. t en bable that the water is condenfed tnt.o c I [i-e~ce into larcrer drops, which ir:lmcdlatcly f 1 f cleEl.ricity prevents thetr coa e c ::> the urp us o . . . fuccceds the departure of the !tg~tn~lg. eter finks before rain i~, fidt, bec:wfc a rcgwl~ 5 T he immediate caufe why tle arom f h o1 J a·Jl" which it h:~d difplaced, mull . . l lace 0 t e c ll r l f warm air; brought to us Ill t le p r -f the heicrht of the w::rm atmo phere )e o . I lighter both fpecifically an. d ab,olu~ely, lid ::,And f-:condly, alter th<.: drops wetg 1 ' f tl prc:cedmcr co or.e. 1 . d fu ofcd to bt: equal to that o le . ot column becomes lighter, the fa \mg rops fpp ·n beain to fall in any column of.al:, tha . . to the rcfifl:ance which they meet o rat o 111 f the air m proportton only adding to the pre ure o . . . h . paffir.g throu gh that flUJd. . - . h t heat or itl very low degrees Wit m '- b diffolved 111 au· Wlt ou ' li . If we could fuppoic water to e . . 1 pens in many chemical olutJOns, . ld become hcaviet' as lap - l r I f h t I [uppofe the alr won I .· be mixed with an aena tO u-o ca ' . of heat, orca Oltque, . . {l: but if water cliffoll'ed 111 the matter r. h . 'confifl:incr of fuch a mixture mu b d ubt but an atmotp etc. o fl: u.o n of water ' th. ere can c. no o tl quanti.t y of ca Io n.q ue. On the fame circum :mcc become lighter tn proportion to le h b th of animals in cold weather, or . roduced from t e rea {l: 1 rlepends the vdible vapour p - f ld - ;vith which it is mixed, ea a part from a boiling kett1. e; ·'[1 e pa rtlcl es o . co . air, v t re whence part o f t h c water h [i I ratfed Ill tempera ll , "f - of its heat, and become t em eves. h "f . reat quantity finks to the ground; 1 ~n is precipitated in ,jfib1e vapour, ~hlc : I. Ill g - Dy faturated, it fpreads itfdf 1111 fmall quantity, and the furroundmg au- IS not prevwu it bec0 mes again diflolved. ( 71 ) NOTE XXVI.--SPRINGS. Your luG-id bands conderife with fingers chill The blue wijf hoveri11g round the gelid hill. CANTO III. 1. 19· THE furface of the earth confifl:s of fl:rata, many of which were formed originally beneath the fea, the mountains were afterwards forced up by fubterraneous fires, as appears from the fiffures in the rocks of which they confifl:, the quantity of volcanic productions all over the world, and the numerous remains of craters of volcanos in mount:~inous countries. Hence the fl:rata whiLh compofe the fides of mountains lie flanting downward!', and one or two or more of the external fl:rata not reaching to the fummit when the mountain was raifed up, the fecond or thirci fl:ratum or a more inferior one is thnc expofetl to d:1y; this may be well reprefcnted by forceably thrufl:ing a blt1nt infhumcnt through fevcrallheets of paper, a bur will Hand up with the lowermofl: fheet fl:anding highefl: in the center of it. On this uppermofl: fl:ratum, which is coldrr as it is more elevated, the dews arc condenfed in large quantities; and f!iding down pafs under the fir!l or fccond or third fl:ratum which compofe the fides of the hill; and eicher form a morafs below, or a weeping rock, by oozing out in numerous places, or many of thefe lefs currents meeting together burll: nut in a more copious rill. . The fummits of mountains are much colder than the phins in their vicinity, owing to feveral caufes; I. Their being in a manner infulated or cut off from the common heat of the earth, which is always of 48 degrees, and perpetually countcratl:s the efFects of external cold beneath that degree. 2. From their furfaces being larger in proportion to their folid contents, and hence their heat more expeditiouDy carried away by the ever-moving atmofphere. 3- The increafing ratiry of the air as the mountain rifes. .i\11 thofe bodies which conduct cletl:ricity well or ill, conduct the matter of heat likewife well or ill. See note VII. Atmofpheric air is a bad condutl:or of tletl:ricity, and thence confines it on the body where it is accumulated, but when it is made very rare, as in the exhaufl:ed receiver, the electric aura pailcs away immediately to any diltance. The fame circumfl:ance probab ly happens in rdpetl: to heat, which is th •1s kept by the clenfer air on the plains from efLaping, but is (IJfTipated on the hills whue the air is thinner. 4· As the currents of air rife up the {ides of mountains they become mechanically rarefied, the prelfure of the incumbent column lelfening as tlwy afcend. Hence the expanding air abforbs heat from the mountain as it afcentl , as explained in note VII. 5· There is another, and perhaps more powerrul caufe, 1 fufpctl:, which may o~ca£ion the great cold on mountain ~, and in the higher parts of the atmofph::re, ;:nd whtc~ has not yet been attended to; 1 mean that the tluitl matter of heat may pro.b:tu!y gr~v1tare round the earth, :.nd form an atmofphere units furf:tce, mixed with the aenal a.tnwJphere, which may diminilh or become rarer, as it recedes from the earth's furface, Ill a greater proportion than the air dimirufhes. |