16 CLIMATE AND RESOURCES OF 



this particular seems to be almost identical with that of light. 

 The rougher the surface of any object, and the more irregu- 

 larities it possesses, the greater is its power of absorption and 

 radiation of heat, and the less its power of reflection. On 

 the other hand, the smoother and harder the surface of any 

 object, the greater is its power of reflection, and the less its 

 power of absorption and radiation. 



Again, the power of retaining heat possessed by any object is 

 also in inverse ratio to its power of absorption and radiation ; 

 thus rocks and hardened baked earth, which require some 

 length of time to become thoroughly heated, from the great 

 amount of heat thrown off their surfaces by reflection, when 

 heated, require also a long time to cool down again. The terms 

 length of time and long time here used are merely compara- 

 tive, and are used as contrasted with the time required by 

 loose porous bodies to become heated or cool down again. 



If we were to take two ordinary paving-flags of equal 

 density and similar composition, and reduce one to powder 

 and leave the other whole, and spread the powder resulting 

 from pulverization over the same extent of surface it occupied 

 before being reduced to powder, we should find that its 

 power of reflecting and retaining heat had been decreased, and 

 its power of absorbing and radiating heat had been increased ; 

 and we should have a standard to compare it with in the flag 

 left unbroken. 



The above experiment will show the difference that takes 

 place in the absorptive and radiative powers, and consequently 

 in the powers of reflecting and retaining heat, by reducing a 

 stone to powder, that is by changing its density ; but I have 

 said the stones should be of similar composition, as different 

 stones and soils have very different powers of absorption and 

 radiation, which must not be overlooked. 



Marsh, in his book " Man and Nature/' in a note on page 



