influenced by the Distribution of Land and Water. 185 



going towards the land. In some places the mean annual tem- 

 perature of the water close to the land is 24°*5 Centigrade ; 

 further out at sea it is 25°, and still further from the land it is 

 25°'5. In other places it gradually augments from 26°, in going 

 from the land, up to 27°'4*. These results are unconnected with 

 the influence of latitude; and they are still less exjalicable by the 

 influence of centrifugal force, in driving the cooler and heavier 

 waters towards the edges of the great current, in its semi- 

 rotatory movement around the gulf; for in this case the law 

 of decrease of temperature in going from the land, should not 

 hold on approaching the coasts of large islands situated towards 

 the centre of the moving mass of waters. But in such instances 

 it is also manifested ; for on the north and south coasts of the 

 Island of Cuba we find the isothermal lines of 26°'2 and 26°"5, 

 while the isothermals of 26°"7 and 2G°-8 are situated outside them 

 respectively f. In M. Deville's chart these are closed isothermals, 

 similar to those which I have indicated on the surface of the 

 British Islands ; but as the lowest isothermals in my map are 

 the most remote from the sea, so those in his chart which exhibit 

 the highest temperature are furthest from the land. It is thus 

 apparent that the intertropical sea may become a storehouse of 

 heat, by retaining much of what it receives from the sun, v/hich, 

 but for the physical properties of water, it would, like the inter- 

 tropical land, lose by radiation into space. It is important co 

 bear this conclusion in mind in any inquiries respecting the in- 

 fluence of the distribution of land and water on general climate, 

 especially as the influence of the land seems to have been hitherto 

 principally considered as a calorific agent. 



The heating action of intertropical land has been so often dis- 

 cussed by writers on climate, that it is unnecessary to do more 

 than to point out its principal agency in the production of aerial 

 currents, by which exchanges of temperature may be promoted 

 between different parts of the earth's surface. 



In contrasting the mean temperature of the sea with that of 

 the land in tropical climates, the want of nocturnal observations, 

 as referred to by M. Melloni, is peculiarly felt. While the tem- 

 perature of the one is nearly constant, that of the other is liable 

 to considerable fluctuations ; and as our records arc principally 

 derived from diurnal observations, the results are probably too 

 favourable to an excess of land temperature. This conclusion 

 is confirmed by the results exhibited in M. Deville's map, and 

 in some measure by the fact of the higher mean temperature of 



* Reduced to dej^rees of Fahrenlieit's scale, these numbers, arranged in 

 the same order as in the text, are l('f\, irO, 77°!>, 7H° H, Hl°;i 



t Eciuivalent respectively to TJ''\(i, 7y'7,BO°06, and 80°-2-l of Fahreu- 



P/iiLMaf/. S. 4. Vol. 17. No. 113. March 1809. O 



