the Distribution of Heat over the Globe. 101 



have seen at once that the low temperature of the land in high 

 latitudes in comparison with that of the sea was no index whatever 

 as to how much the temperature of those regions would sink 

 were the sea entirely removed and the surface to become land ; 

 for the present high temperature of the sea is not due wholly to 

 the mere physical properties of water, but to a great extent is 

 due to the heat brought by currents from the equator. Now, 

 unless it is known how much of the absolute temperature of the 

 ocean in those latitudes is due to currents, we cannot tell how 

 much the removal of the sea would lower the absolute tempera- 

 tare of those places. Were the sea removed, the continents in 

 high latitudes would not simply lose the heating advantages 

 which they presently derive from the mere fact of their proximity 

 to so much sea, but the removal would, in addition to this, de- 

 prive them of an enormous amount of heat which they at pre- 

 sent receive from the tropics by means of ocean-currents. And, 

 on the other hand, at the equator, were the sea removed, the 

 continents there would not simply lose the cooling influences 

 which result from their proximity to so much water, but, in ad- 

 dition to this, they would have to endure the scorching effects 

 which would result from the heat which is at present carried away 

 from the tropics by ocean-currents. 



We have already seen that Professor Forbes concluded that 

 the removal of the sea would raise the mean temperature of 

 the equator 30° and lower the temperature of the poles 28°; it 

 is therefore perfectly certain that, had he added to his result the 

 effect due to ocean-currents, and had he been aware that about 

 one-fifth of all the heat possessed by the Atlantic is actually de- 

 rived from the equator by means of the Gulf-stream, he would 

 have assigned a temperature to the equator and the poles, of a 

 globe all land, differing not very far from what I have concluded 

 would be the temperature of those places were all ocean and 

 aerial currents stopped, and each place to depend solely upon 

 the heat which it directly received from the sun. 



Influence of Ocean-currents shown by a Third method. — The 

 great influence of ocean-currents in lowering the temperature of 

 the equator and raising the temperature of the poles can also be 

 shown in still another way. 



The general influence of land on climate is to exaggerate the 

 variation of temperature due to the seasons. On continents the 

 summers are hotter and the winters colder than on the ocean. 

 The days are also hotter and the nights colder on land than on 

 sea. This is a result which follows from the mere physical pro- 

 perties of land and water, independently of currents, whether of 

 ocean or of air. But it nevertheless follows, according to theory 

 (and this is a point which has been overlooked), that the mean 



