§454, 455. THE SPECIFIC GRAVITY OF THE SEA, ETC. 229 



ceived by the earth is about Yt niore than it receives during a day 

 in July, when it is in aphelion."^ January is the midsummer month 

 of the southern hemisphere, consequently that half of the globe / 

 receives more heat in a day of its summer than the other half re- 

 ceives in a day of the northern summer. But the northern sum- 

 mer is a week the longer, by reason of the ellipticity of the earth's 

 orbit. What becomes of this diurnal excess of southern summer 

 heat, be it in its aggregate never so small, and why does it not ac- 

 cumulate in trans-equatorial climes ? So far from it, the southern 

 hemisphere is the cooler. 



454. In the southern hemisphere there is more sea and less I. 

 The latent heat of ^^^^ ^^^^ i^ t^® northern. But the hydrometer 

 ^^^^^- indicates that the water in the seas of the former 



are salter and heavier than the waters of seas cis-equatorial ; and 

 man's reasoning faculties suggest, in explanation of this, that this 

 difference of saltness or specific gravity is owing to the excess of 

 evaporation in the southern half, excess of precipitation in the 

 northern half of our planet. " When water passes, at 212° Fahr- 

 enheit, into steam, it absorbs 1000° of heat, which becomes insen- 

 sible to the thermometer, or latent ; and conversely, when steam 

 is condensed into water, it gives out 1000° of latent heat, which 

 thus becomes free, and affects both the thermometer and the ■ 

 senses. Hence steam of 212° Fahrenheit will^ in condensing, heat 

 five and a half times its own weight of water from the freezing to 

 the boiling point." — M^Culloch. Now there is in the southern a 

 very much larger water surface exposed to the sun than there is 

 in the northern hemisphere, and this excess of heat is employed 

 in lifting up vapor from that broad surface, in transporting it 

 across the torrid zone and conveying it to extra-tropical northern 

 latitudes, where the vapor is condensed to replenish our fountains, 

 and where this southern heat is set free to mitigate the severity 

 of northern climates. 



455. In order to trace a little farther, in our blind way, the 

 Its influence upon evidcnccs of wisdom and design, which we imagine 

 climates. ^^ ^^^ dctcct in the terrestrial arrangement of land 

 and water, let us fancy the southern hemisphere to have the land 

 of the northern, and the northern to have the water of the south- 

 ern, the earth's orbit remaining the same. Is it not obvious to 



* Sir John Herschel. 



