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MR. T. HOPKINS ON THE INFLUENCE OF SUN-HEATED LAND 



the earth being in parts raised to a high temperature will to 

 some extent communicate that temperature to the air resting 

 upon it, making it rise, and allowing cool air to supply its 

 place, is to a small extent true ; but that this kind of heating 

 of the air produces the important effects ascribed to it, is 

 not shown by reference to any known facts. It is therefore 

 to be viewed as only a plausible conjecture which has been 

 advanced and adopted in the absence of sufficient real know- 

 ledge of the subject. 



I have, in former papers, shown that the influence of such 

 heating of the land as has been referred to, on the atmosphere, 

 is feeble and incapable of producing the strong winds, including 

 those called the trade winds, that blow in many parts of the 

 world ; but it is desirable that we should go more fully into 

 the subject, and trace more particularly the real effects of 

 heating the surface of land by the sun, on the air resting 

 on the land. It must be observed that it is not merely the 

 geographical position of the tropics that is supposed to cause 

 the air to rise, but the high temperature of the surface of the 

 land, and of the air resting upon it, as a consequence of that 

 position. It therefore follows that where the surface is the 

 most heated by direct solar influence, the effect spoken of 

 should be experienced in the highest degree; and the large 

 areas on the earth's surface which are the most heated should 

 have the air over them the most swelled and buoyed up, 

 allowing cold air to flow towards them below in tiie most 

 palpable and decided manner. Now there are a number of 

 such places respecting which we have tolerably full informa- 

 tion, and all that is necessary to be done, is, that we should 

 collect that information, and ascertain the nature of the evi- 

 dence which it furnishes relating to the truth or the falsity 

 of the theory under consideration. 



It is well known that it is not upon the equatorial belt that 

 the most highly sun-heated land is found, or where such lands 

 exist to the greatest extent, though most of them are within 



