204 On Salar Radiation. 



would make the sensible heat seem much greater than the 

 true temperature. 



It is also known, that the soil in some situations between 

 the tropics has a very high degree of temperature when ex- 

 posed to the full action of the sun's rays, 180° degrees of 

 Farhenheit I think is recorded by Sir John Herschel at the 

 Cape, in a recent work on horticulture by Lindley, if I re- 

 member correctly. When it is considered that in this case 

 the cooling contact of the atmosphere can only act upon the 

 same extent of surface as is exposed to the action of the 

 sun's rays, it is not improbable that the temperature result- 

 ing may be much greater than that of an insulated mass, 

 which presents to the cooling contact of the air a surface 

 increasing as the cube of its diameter, while the surface ex- 

 posed to the action of the sun's rays increases only as the 

 square. 



Perhaps a closed tin cylinder painted black, and rilled 

 with water, or an iron shell, might answer well for observing 

 the effects of solar radiation; but before an unit of com- 

 parison can be hit upon, many experiments are required, 

 and the research necessary will be almost out of the power 

 of a single individual. Our information upon the heating 

 and cooling of bodies in the air also is not very extensive ; 

 but it would seem that the velocity of cooling is inversely as 

 the cube of the diameter, and that it is not affected by the 

 nature of the surface, (Encyclopedia Metropolitania, article 

 Heat.) 



In this imperfect paper I have purposed principally to call 

 the attention of scientific men to the subject, and to notice 

 these points on which information is principally required; 

 and I shall have much pleasure in co-operating with any 

 gentlemen who will give the subject attention, as soon as 

 any fixed plan of observation has been agreed upon. 



