222 PHYSICAL GEOGRAPHY OF THE SEA, AND ITS METEOROLOGY. 



relation between the orbit of the earth and the arrangement of land 

 and water on its surface and their bearing upon climate. Om- planet 

 passes its perihelion during the southern sinnmer, when it is nearer 

 the centre and somxe of hght and heat by more than three millions 

 of miles than it is at its winter solstice, so that, on the 1st of 

 January, the total amount of heat received by the earth is about 

 ■J5- more than it receives during a day in July, when it is in aphe- 

 lion.* January is the midsummer month of the southern hemi- 

 sphere, consequently that half of the globe receives more heat in a 

 day of its summer than the other half receives in a day of the 

 northern summer. But the northern summer is a week the longer, 

 by the reason of the ellipticity of the earth's orbit. AYhat becomes 

 of this dim-nal excess of southern summer heat, be it in its aggre- 

 gate never so small, and why does it not accumulate in trans- 

 equatorial chmes ? So far from it the southern hemisphere is the 

 cooler. 



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

 The latent heat of than in the northern. But the hydrometer indicates 



vapour. ^]^Q^^ j^i^Q water in the seas of the former are Salter and 



heavier than the waters of seas cis-equatorial ; and man's reason- 

 ing faculties suggest, in explanation of this, that this difference of 

 saltness or specific gravity is o^ving to the excess of evaporation 

 in the southern half, excess of precipitation in the northern half of 

 our planet. "When water passes, at 212^ Fahrenheit, into steam 

 it absorbs 1000^ of heat, which becomes insensible to the ther- 

 mometer, 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 

 o^Ti weight of water from the fi^eezing to the boiling point." — 

 M'CuIIoch. Now there is in the southern a very much larger 

 water smface exposed to the sun than there is in the northern hemi- 

 sphere, and this excess of heat is employed in lifting up vapom- from 

 that broad smface, in transporting it across the torrid zone and 

 conveying it to extra-tropical northern latitudes, where the vapour 

 is condensed to replenish om' 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 evi- 

 its influence upon deucos of wisdom and design, which we imagine we 

 climates. qcj^^ dctect in the terrestrial arrangement of land and 



* Sir John Herschel. 



