concerning Heat. 147 



those results which it ought to have exhibited, on the 

 supposition that heat is propagated, even in the interior 

 of solid bodies, by radiations emanating from the sur- 

 faces of the particles composing these bodies. 



On this supposition, we must necessarily consider 

 the particles that compose bodies as being separate from 

 each other, and even by pretty considerable distances, 

 compared with the diameters of these particles ; but 

 there is nothing repugnant to the admission of this sup- 

 position ; on the contrary, there are many phenomena 

 which apparently indicate that all the solid bodies with 

 which we are acquainted are thus formed. 



To see now by what law heat would be propagated 

 in a solid cylinder, let us represent the axis of this cylin- 

 der by a right line A E, Plate IV. Fig. i ; and let 

 us begin with supposing that the cylinder consists of 

 three particles of matter only, ACE, placed at equal 

 distances in that line. 



Let us farther suppose that the extremity, A, of the 

 cylinder is constantly at the temperature of boiling water, 

 while its other extremity, E, remains invariably at the 

 freezing point. 



By an experiment, of which I have already given an 

 account to the Class,* I found that when two equal 

 bodies, A B, one hotter than the other, are isolated and 

 placed opposite each other, the intensities of their ra- 

 diations are such, that a third body, C, placed in the 

 middle of the space that separates them, will acquire a 

 temperature, by the simultaneous action of these ra- 

 diations, which will be an arithmetical mean between 

 those of the two bodies A and B. 



From the result of this experiment we have ground 



* See the preceding paper. 



