510 Prof. E. Edlund on the Thermal Phenomena of the 



What is hero advanced can of course be applied to any mo- 

 lecule whatever that is sufficiently near to the contact- 

 surface. 



We now assume that the electric fluid consists of the lumi- 

 ferous aether, and that the heat of a body is caused, at least 

 a given portion of it, by the vibrations of the aether mole- 

 cules about their positions of equilibrium *. The quantity 

 of heat contained by the body is then determined by the 

 sum of the vis viva of the molecules ; and its temperature, 

 reckonecj from absolute zero, can be regarded as proportional 

 to this sum ; for the deviation that may take place does not 

 affect the final result. If the body at an ordinary tempera- 

 ture receives an inconsiderable elevation of its degree of heat, 

 e. g. from 10° to 20°, there are no physical grounds for the 

 assumption that the period of a vibration of the molecules is 

 thereby altered ; on the contrary, it must remain unaltered, 

 because the elasticity-forces, on which the motion and the 

 rate of vibration depend, cannot thereby undergo any sensible 

 change. On the other hand, the amplitudes of the molecule- 

 vibrations are augmented by the small rise of temperature, 

 while the path remains of the same form as at the lower tem- 

 perature. The vibration-paths of the aether molecules also 

 satisfy the condition stated, that they be divided into two 

 equal halves by a plane which passes through the position of 

 equilibrium of the molecules and is parallel to the surface of 

 contact between M and N. But if the increment of tempe- 

 rature is great, experiment shows that not only is the time of 

 a vibration of the molecules lessened, but also the molecules 

 of the body change their position and increase their distance 

 from each other. Therefore it is only for slight increments 

 of temperature that the above conclusion can be applied to 

 the calculation of change of attraction. It is self-evident 

 that p 2 is proportional to the vis viva of the aether molecules, 

 and therefore that, if T denotes the absolute temperature of 

 the body, we can write p 2 =/T, where / signifies a constant. 

 If A is the amount of the attraction at the temperature T , 

 and A x at the somewhat higher temperature T 1? we get 



A 1 -A =D(T 1 -T ), 



in which D is a constant which depends inter alia on the 



* The heat possessed by a body is doubtless occasioned also in part by 

 the vibrations of the body's own molecules ; yet it is readily seen that the 

 variation of the attraction which results from the vis viva of the material 

 molecules need not be taken into account, because the action of this varia- 

 tion, when a thermoelectrical ricg is in question, becomes, for the entire 

 ring, equal to nil. 



