concerning Heat. 149 



particle D be in cooling it, the temperature of the particle 

 C ought not to be changed. But experience has shown 

 that, at equal distances and equal intervals of tempera- 

 ture, the calorific influences of hot bodies and the frigo- 

 rific influences of cold bodies are exactly equal ; and as 

 the distance from B to C is equal to the distance from 

 D to C, while the interval of temperature between B 

 and C, = 45, is the same as that between D and C, 

 = 45, it is evident that the temperature of the par- 

 ticle C, which is in the middle of the cylinder, can be 

 no way affected by the introduction of the intermediate 

 particles B and D. 



By the same way of reasoning may be proved, that 

 the introduction of an indefinite number .of . interme- 

 diate particles would produce no change in the tempera- 

 ture of the middle of the axis of the cylinder, or in any 

 part of it; and if the introduction of an indefinite num- 

 ber of intermediate particles make no change in the state 

 of a thermometer placed in the middle of the axis of 

 the cylinder, we may conclude that the thermometer 

 would remain equally stationary if the number of inter- 

 mediate particles were increased till they had that prox- 

 imity to each other which is necessary to constitute a 

 solid body. If, instead of a single row of particles in a 

 right line, there were a bundle composed of an indefinite 

 number of such rows placed side by side, forming a 

 solid cylinder, the temperature in the different parts of 

 the line A E would remain the same. 



From this reasoning we may infer that the tempera- 

 tures of the different parts of the cylinder should de- 

 crease in arithmetical progression from one extremity 

 of the cylinder to the other. 



But it is evident that this law of decrement of tern- 



