VI. 



ON AN ALLEGED EXCEPTION TO THE SECOND LAW OF 



THERMODYNAMICS. 



[Science, vol. i, p. 160, Mar. 16, 1883.] 



ACCORDING to the received doctrine of radiation, heat is transmitted 

 with the same intensity in all directions and at all points within any 

 space which is void of ponderable matter and entirely surrounded 

 by stationary bodies of the same temperature. We may apply this 

 principle to the arrangement recently proposed by Prof. H. T. Eddy * 

 for transferring heat from a colder body A to a warmer B without 

 expenditure of work. 



In its simplest form the arrangement consists of parallel screens, 

 which are placed between the bodies A and B, and have the form of 

 very thin disks with certain apertures, and the property of totally 

 reflecting heat. These disks, or screens, are supposed to be fixed on 

 a common axis, and to revolve with a constant velocity. For the 

 purposes of theoretical discussion, we may allow this velocity to be 

 kept up without expenditure of work, since we may suppose the 

 experiment to be made in vacuo. If the dimensions and velocity of 

 the apparatus are such that the screens receive a considerable change 

 of position during the time in which radiant heat traverses the 

 distances between them, the apertures in the screens may be so placed 

 that radiations can pass from A to B, but not from B to A. It 

 is inferred that it is possible, by such means, to make heat pass from 

 a colder to a warmer body without compensation. 



In order to judge of the validity of this inference, let us suppose 

 thermal equilibrium to subsist initially in the system, and inquire 

 whether the motion of the screens will have any tendency to disturb 

 that equilibrium. We suppose, then, that the screens, the bodies A 

 and B, and the walls enclosing the space in which the experiment is 

 made, have all the same temperature, and that the spaces between 

 and around the screens and the bodies A and B are filled with the 

 radiations which belong to that temperature, according to the prin- 

 ciple cited above. Under such circumstances, it is evident that the 

 presence of the screens, whether at rest or in motion, will not have 



* Journ. Frankl. Inst., March, 1883. 



