58 Scientific Proceedings, Royal Dublin Society. 



when it reaches it, this radiant heat will get into B. While % was 

 open, however, some heat left B ; but as Dr. Eddy observes, y may 

 be closed so as not to let this even get through the screen m, and it 

 can be all returned into B by reflection through s or some other 

 aperture. So far I entirely agree with Dr. Eddy, and so far it 

 seems as if the result had been to transfer heat from A to B with- 

 out B's losing any heat by having it transferred to A. As I 

 warned Dr. Eddy when I heard his Paper, there are, however, 

 other bodies and regions to be considered besides A and B. There 

 are more than two bodies considered : there is the region of the 

 screens. Consider what happens when the heat that escaped out of 

 B into the mn region tries to get back into B. Some door must be 

 opened to let it pass, and, while it is passing in, an, at least, equal 

 amount of heat will be passing out of B into the mn region, so that 

 you can never really get the heat that has once left B back into B 

 again. This is true whether you adopt doors over fixed apertures 

 such as I have supposed, or moving apertures such as Dr. Eddy 

 proposed. What really takes place is this : a certain quantity of 

 heat escapes out of A and reaches B, and a not less quantity of heat 

 leaves B and is kept entangled in the region of the screens, and it 

 is only possible to let the heat pass from A to B by means of this 

 third region. Hence this only really comes to the same thing as 

 letting A radiate some of its heat into the screen region while B is 

 kept closely shut up. Now be it observed that Dr. Eddy practi- 

 cally postulates that this screen region is at least colder than A — in 

 fact he assumes' it to be perfectly cold, i. e. to contain no radiant 

 heat except what is admitted from A and B, so that it is by no 

 means contrary to the theory of exchanges that A might cool by 

 radiating into this region. 



This seems to me to be a perfectly satisfactory explanation of 

 what would take place, though it, for the present, dispels the 

 vision of an immortal universe. This experiment of Dr. Eddy's, 

 however, seems to call attention to the fact that a region of motion- 

 less ether must be considered as practically a cold body capable of 

 absorbing radiations. 



