444 THE PHYSICAL GEOGRAPHY OF THE SEA : 



in the antarctic circle peculiarly favorable to heavy and almost 

 incessant precipitation. But, before describing these conditions, 

 let us turn aside to inquire how far precipitation in the supposed 

 cloud region of the south may assist in giving force and regularity 

 to the winds of the southern hemisphere. 



829. If we take a measure, as a cubic foot, of ice at zero, and 

 The latent heat of ^PP^J ^^^^ ^o it by mcaus of a stcady flame that 

 ^^P"'"' will give off heat at a uniform rate, and in such 

 quantities that just enough heat may be imparted to the ice to 

 raise its temperature 1° a minute, we shall find that at the end of 

 32 minutes the ice will be at 32°. The ice will now begin to 

 melt ; but it and its water — the heat being continued — will remain 

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

 at 32°.* This 140° of heat, which is enough to raise the temper- 

 ature of 140 cubic feet of ice one degree from any point below 32°, 

 has been rendered latent in the process of liquefaction. 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 converted into water at 32°, 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 

 will remain for 1030 minutes, notwithstanding the continuous sup- 

 ply of heat during the interval. At the expiration of this 1030 

 minutes of boiling heat, the last drop of water will have been con- 

 verted into steam ; but the temperature of the steam will be that 

 only of the boiling water ; thus, in the evaporation of every meas- 

 ure of water, heat enough is rendered latent during the process to 

 raise the temperature of 1030 such measures one degree. If this 

 vapor be now condensed, this latent heat will be set free and be- 

 come 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, amount- 

 ing to enough to raise the temperature of 140 additional drops 

 one degree, is also set free. 



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



* See Espy's Philosophy of Storms. 



