TKADE-WINDS OF THE SOUTHERN HEMISPHERE. 3^5 



water again, and tliis latent lieat will become sensible heat, for 

 heat no more than ponderable matter can be annihilated. 



But if, after the cubic foot of ice has been converted into water 

 at 82°, we continue the uniform supply of heat as before and at the 

 same rate, the water will, at the expiration of 180 minutes more, 

 reach the temperature of 212° — the boiling point — and at this 

 temperature it wiU remain for 1030 minutes, notwithstanding the 

 continuous supply of heat during the interval. At the expiration 

 of this 1030 minutes of boihng heat, the last drop of water will 

 have been converted into steam ; but the temperature of the steam 

 will be that only of the boiling water; thus, in the evaporation of 

 every measure of water, heat enough is rendered latent during the 

 process to raise the temperature of 1030 such measures one de- 

 gree. If this vapor be now condensed, this latent heat will be set 

 free and become sensible heat again. 



Hence we perceive that every rain-drop that falls from the sky 

 has in its process of condensation evolved heat enough to raise 

 one degree the temperature of 1030 rain-drops. But if, instead 

 of the liquid state, as rain, it come down in the solid state, as hail 

 or snow, then the heat of fluidity, amounting to enough to raise 

 the temperature of 140 additional drops one degree, is also set free. 



We have in this fact a clew to the violent wind which usually 

 accompanies hail-storms. In the hail-storm congelation takes 

 place immediately after condensation ; and so quickly that the 

 heat evolved during the two processes may be considered as of 

 one evolution. Consequently the upper air has its temperature 

 raised much higher than could be done by the condensing only. 



But this is digressive. Therefore let us take up the broken 

 thread, and suppose, merely for illustration, such a rain-fall as 

 King and Fitzroy encountered in Patagonia to have taken place 

 under the supposed cloud region of the antarctic circle, and to 

 have been hail or snow instead of rain, then the total amount of 

 caloric set free among the clouds, in those 41 days of such a 

 flood, would be enough to raise from freezing to boiling six and a 

 half times as much water as fell. But if the supposed antarctic 

 precipitation come down in the shape of rain, then the heat set 

 free would be suficient only to raise from freezing to boiling 

 about 5f as much water as the flood brought down. 



1017. "We shall have perhaps a better idea of the amount of heat 



