G4 report — ISGl. 



the oToat expani?(3 of southorn waters affords tlie vapoiii's; and yet, in the conden- 

 sation of the vapour for tlio rains to feed these rivers, he.xt enoiip^h is set free in the 

 clouds to raise from tlie freezinc- to tlie boilini>--point, and as fast as it flows, more 

 tlian live times the volume of water that the said rivers discharge into the sea. 



But how the latent heat of vapom* when set free in the clouds may reach down 

 and wai-m the earth, may perhaps be understood by referring to a meteorological 

 necessit}-, which rec[iures, tcJwn the windward side of the mountain is rainy, the lee 

 side to be irarm. 



To illustrate this, let us suppose a gossamer sack, capable of being hermetically 

 sealed ; that it is impervious to heat, and elastic as the air itself ; that with the 

 barometer at 30 in., tlie temperature at 60^, and the dew-point the same, this sack 

 be tilled with air ; that then it be attached to a balloon and sent up in the sk}', to 

 a height where the baroraeti-ic pressm-e is only 15 in., and where the temperatm-e of 

 the air in the sack, by reason of this diminished pressm-e, and by virtue of the ex- 

 pansion of the air within and its consequent cooling, is reduced to zero. By this 

 process, the vapoiu" ^vith which the air was loaded when it was admitted into the 

 sack has, let it be assumed, been condensed, and consequently its latent heat set 

 free in the sack. 



Suppose now the sack be hauled down to the surface again, where the barometric 

 pressure is .30 in., as before, and what have we ? The sack is reduced to its fomier 

 dimensions you will perceive, but instead of damp air we now have it filled with 

 dry ; moreover, there is at the bottom a measure of water — the condensed vapour. 

 This chy air, instead of being at the temperatme of CO-*, has a temperatiire of GO^ ^j/ms 

 the quantity of heat that it would require to raise 5A such measures of water from 

 the freezing- to the boiling-point. In other words, we have but illustrated a natm-al 

 process that is continually going on and well understood, by which heat is bottled 

 away in vapoura, wafted by the ^^'iuds from clime to clime, liberated, and iiually, 

 in the processes of vertical cu'culation, drawn do^vni from the ciystal reservoirs of 

 the sky to temper and warm the surfoco of the earth. 



"When the vapour-laden west %\iuds of the South Pacific strike against the wind- 

 ward side of the Patagonian Andes, are they not by nature herself subjected to a 

 process precisely analogous to that of vapour-laden air in the h}iiothetical sack ? 

 Sti'iking against the western slopes of the mountain, they are forced up to the top 

 of the snow-capped range. Here condensation of vapoiu- and the liberation of its 

 latent heat talce place ; and though the cold be extreme at the top, in consequence 

 of the state of aerial rarefaction there, yet the winds lia's'ing received the heat libe- 

 rated from their vapom-s, are, before it can. bo dispei-sed by radiation, forced over 

 from the eastern slopes. Here descending into the valleys, and being again com- 

 pressed by the full weight of the barometiic column, the heat they have received is 

 fully developed, and they are felt as wann -winds, just as the air brought down in 

 the sack was waiiu. The mild climate of Eastern Patagonia and the Falkland 

 Islands is due to caloric thus conveyed, developed and dispei-sed. 



To appreciate the amount of heat thus conveyed and distributed, let ns compare 

 the climate of Eiistem Patagonia, between the parallels of 50^ and 52° south, -with 

 the climate of Labrador, between the corresponding parallels north. Those who 

 would judge of climate, as philosophers formerly did, viz. according to latitude, 

 woidd say these two climates are duplicates of each other, for the two places are 

 equidistant from the Equator, and in both coimtries west -svinds are the prevailing 

 winds ; they both also have a continent to -windward, an ocean to leeward ; llo-wing 

 in from each and along their eastern shores, there is like-ndse an ice-bearing current. 

 But what do modem researches show ? They show that the -winter climate of 

 Labrador is ice-boimd, bitter in the extreme, and incapable of affording vegetable 

 subsistence for man and beast ; that that of Patagonia in the corresponding latitude 

 south is, on the other hand, quite open and mild, affording grasses for cattle all the 

 •winter through. 



How is this ? The two places, though on opposite sides of the Equator, are, let it j 

 be repeated, equidistant fi'om it. They are on the same side of the continent, and the] 

 eame shore of the ocean ; then why should there be such a difference in their -winter I 

 climate ? Investigation answers, simply because of the difference in the quautitv' of I 

 moisture which the prevailing -winds, which also are the same, bring near the twol 

 places for condensation. The west -winds of Labrador, na they cross the Eockyj 



