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



molecules changes with the temperature, and that a conductor, 

 of which one partis hotter than another, does not behave just 

 like a conductor composed of two chemically different metals 

 both possessing the same temperature. For this the follow- 

 ing reason may be given : — 



We will imagine two different conductors M and N in con- 

 tact with one another, and that M exerts a greater attraction 

 than N upon an electrical molecule m. It may here be re- 

 marked en passant that the attraction exerted by a body upon 

 an electrical molecule in its immediate vicinity must depend 

 not merely on the nature of the molecules of the body, but 

 also on their relative position and distance from one another. 

 We will now assume that the molecule m is situated on the 

 same side of the surface of contact as N, and at the distance r 

 from the same surface, and that r does not exceed the distance 

 within which the molecular forces can operate. It is then 

 evident that the force of attraction which tends to carry 

 the molecule m to the surface of contact is increased when the 

 distance from that surface is diminished ; the force reaches its 

 maximum when m is at the surface itself, but again decreases 

 as soon as m removes from it and penetrates into M. Lastly, 

 the force becomes insensible when the molecule m has pene- 

 trated into M so far that the distance from the surface of con- 

 tact attains the magnitude of the action-radius of the molecular 

 attraction-forces. Moreover, the law according to which the 

 attraction increases when in, being in N, is approaching the 

 contact-surface must be similar to the law according to which 

 the attraction decreases when m is in N, and is moving from 

 the surface mentioned. The action of the attraction which 

 in the time 2t tends to bring the molecule m to the surface of 



contact, can then be expressed by -~, in which n denotes the 



power according to which the attraction decreases when the 



distance becomes greater, and a is a constant. The expression 



2at 



—^ denotes the increment of quantity of motion which the 



molecule m would receive if it were free and conld move, and 



if a determinate invariable force— n acted upon it during the 



time 2t . If we now imagine the molecule m at the distance 

 r— pfrom the contact-surface, this attraction during the time 



t will be expressed by - ^- , and at the distance r + p the 



attraction during an equal period by— — °-yi. Therefore, if the 

 molecule m be first during the time t at the distance r—p 



