1 20 Inquiry concerning the Nature of Heat, 



the difficulty of explaining how, or by what mechanism, 

 it can be possible for the same body to receive and 

 retain, and reject and drive away, the same kind of sub- 

 stance, at one and the same time (an operation not 

 only incomprehensible, but apparently impossible, and 

 to which there is nothing to be found analogous, to 

 render it probable), many other reasons might be brought 

 to show that this hypothesis of the supposed continual 

 interchanges of caloric between neighbouring bodies is 

 very improbable; and, among the rest, there is one which 

 appears to me to be quite conclusive. 



As the point in dispute seems to be of great impor- 

 tance to the science of heat, I shall endeavour to ex- 

 amine it with all possible attention; and, in order to 

 put the hypothesis in question to the test, we will see 

 if it will accord with the results of some of the fore- 

 going experiments, which, in order to their being more 

 easily comprehended and examined, I shall elucidate by 

 figures. 



Let the two opposite ends of the cylinders A and B 

 (Plate III. Fig. 4) represent the two vertical metallic 

 disks of equal dimensions, which were presented at the 

 same time to the ball of the thermoscope C, in the ex- 

 periment No. 23. 



In that experiment the disk A being at the tempera- 

 ture of 32 F. (that of freezing water), and the disk B 

 at 112 F., while the ball of the thermoscope C and all 

 other surrounding bodies were at 72, it was found that 

 the temperature of the thermoscope was not changed by 

 the simultaneous actions of these two bodies, the one 

 hot and the other cold. 



In order to account for this result on the hypothesis 

 before mentioned, we must begin by supposing that the 



