444 ruYSicAL CEOGiiArHY OF thp: sea, and its meteorology. 



melt ; but it and its water, tbe heat being continued, will re- 

 laain at 32° for 140 minutes, when all the ice will have become 

 water at o2°*. This 140^ of heat, which is enough to raise the 

 temperature of 140 cubic feet of ice one degree from any point 

 below 32°, has been rendered latent in the process of liquefac- 

 tion. Freeze this water again, and this latent heat will become 

 sensible heat, for heat no more than ponderable matter can be 

 annihilated. But if, after the cubic foot of ice has been con- 

 verted into water at 32°, we continue the uniform suppl}^ 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 will remain for 1030 minutes, 

 notwithstanding the continuous supply of heat during the in- 

 terval. At the expiration of this 1030 minutes of boiling 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 tem- 

 perature of 1030 such measures one degree. If this vapour 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, evolvexi 

 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. 



830. Tlie cause of the boisterous weatlicr off Cape Horn. — We 

 have in this fact a clew to the violent wind which usuall}^ accom- 

 panies 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. 

 So also the storms which have made Cape Horn famous are no 

 doubt owing, in a great measure, to this heavy Patagonian rain- 

 fall. The latent heat which is liberated by the vapour as it is 

 condensed into rain there, has the effect of producing a great in- 

 tumescence in the air of the upper regions round about them, 



* See Espy's riiilosopby of Storms. 



