34?8 Note by M. Ampere on Heat and Light. 



posed for the transmission of heat, —it is evident that we shall 

 find for the transmission of this force in the systems of diapa- 

 sons the same equations at which those philosophers have ar- 

 rived for temperature agreeably to their respective hypotheses. 



Let us observe here, that so long as we consider the dia- 

 pasons as having sensibly but one single dimension, we are 

 obliged to subject them to the condition of being capable of 

 vibrating in unison ; but as M. Savart has demonstrated that 

 vibrating forces of two dimensions, and with greater reason 

 vibrating bodies of three dimensions, are susceptible, by gra- 

 dual changes in the nodal lines, to take the unison of any vi- 

 brating body whatever, it suffices here to substitute, in every- 

 thing that precedes, the name of diapason for that of a vibra- 

 ting plate or solid, in order to find true everything we have 

 been saying, without any condition relative to the form or di- 

 mension of the bodies. 



Let us now apply this to the molecules of a heated body, 

 considering these molecules as so many diminutive solids 

 susceptible of vibrating independently of one another, and of 

 communicating gradually parts of the vis viva of their motion 

 to the surrounding aether, producing in it an undulation or 

 wave at every vibration, precisely as a diapason communicates 

 one part of the vis viva of its vibratory motion to the sur- 

 rounding air; and let us admit that it is only through the me- 

 dium of this aether that a neighbouring molecule, which has 

 a less intense vibratory motion, increases gradually its vis viva 

 in proportion as this force is inferior to the force of the first 

 molecule; it is evident that we shall find, by the distribution 

 of the vis viva among the different molecules, precisely the 

 same equations as those which have been given for the distri- 

 bution of heat, according to the different hypotheses respect- 

 ing the manner in which the vis viva transmitted from one 

 molecule to another depends upon the difference in their tem- 

 peratures. 



We find manifestly the same result by considering the sub- 

 ject as we have just enunciated it, according to the system of 

 emission, or according to that of vibrations, substituting for 

 the quantity of caloric in the first system, the vis viva of the 

 vibratory motions of the molecules in the second. It was in 

 order to render the analogy between the propagation of heat 

 in bodies and that of sonorous vibrations from solid to solid, 

 through the medium of the air, more easy of comprehension 

 that I supposed in this explanation that the molecules of 

 bodies do not transmit their vibratory motions one to another, 

 except through the medium of the aether: but I think that 

 the molecules can also transmit heat one to another [inane- 



