EXCEPTION TO SECOND LAW OF THERMODYNAMICS. 405 



any influence upon the intensity of the radiations passing through 

 the spaces between and around them; since the heat reflected by a 

 screen in any direction is the exact equivalent of that which would 

 proceed in the same direction (without reflection) if the screen were 

 not there. So, also, the heat passing through any aperture in a screen 

 is the exact equivalent of that which would be reflected in the same 

 direction if there were no aperture. The quantities of radiant heat 

 which fall upon the bodies A and B are therefore entirely unchanged 

 by the presence and the motion of the screens, and their temperature 

 cannot be affected. 



We may conclude a fortiori that B will not grow warmer if A 

 is colder than B, and none of the other bodies present are warmer 

 than B. 



Since the body A, for example, when the screens are in motion, 

 does not receive radiations from every body to which it sends them, 

 it is not without interest to inquire from what bodies it will receive 

 its share of heat. This problem may be solved most readily by sup- 

 posing the screens to move in the opposite direction, with the same 

 velocity as before. One may easily convince himself that every body 

 which receives radiant heat from A when the apparatus moves back- 

 ward, will impart heat to A when the apparatus moves forward, and 

 to exactly the same amount, if its temperature is the same as that 

 of A. 



