and the Mode of its Communication. 121 



ball of the thermoscope gives off radiant caloric con- 

 tinually in all directions, and receives it in return from 

 the surfaces of all the bodies by which it is surrounded. 



With regard to all these surrounding bodies (ex- 

 cepting the disks A and B), as they are at the same 

 temperature as the ball of the thermoscope (that of 72), 

 they will give- continually to that instrument just as 

 much radiant caloric as they receive from it, and no 

 change of temperature will result from these equal 

 interchanges. 



But in respect to the disk A, as that is colder than 

 the ball of the thermoscope, it returns to it a smaller 

 quantity of radiant caloric than it receives from it ; 

 consequently the thermoscope receives continually less 

 than it gives : it would of course be gradually exhausted 

 of caloric and become colder were it not for the com- 

 pensation it receives for this loss from the^disk B. This 

 disk, being hotter than the thermoscope, gives to it 

 continually more radiant caloric than it receives from 

 it ; and were it not for the simultaneous loss of caloric 

 which the instrument sustains in its interchanges with 

 the cold disk A, its quantity of caloric would be aug- 

 mented, and it would become hotter. 



Now, as the temperature of the ball of the thermo- 

 scope is an arithmetical mean between that of the disk 

 A and that of the disk B, it is reasonable to suppose 

 that the thermoscope receives just as much more caloric 

 from B than it gives to it as it gives to A more than it 

 receives from it ; and if that be the case in fact, it is evi- 

 dent that the simultaneous actions of the two disks on 

 the ball of the thermoscope (or the traffic which they 

 carry on with it in caloric) can neither tend to increase 

 nor to diminish the original stock of that substance be- 



