14 Trans. Acad. Sci. of St. Louis. 



being the velocity with which the fluid flows in the wire, 

 we shall have an equation similar to the last, or 



On the condenser core, the convection current is carried 

 on a thin film of its surface. In the wire of resistance R, 

 the same current is distributed uniformly over a cross- 

 section s. The relation between the conduction resist- 

 ance R and what may be called the convection resistance is 



2logeP -U 



V , ks 

 When the values of v and p satisfy this equation the 

 potential of the condenser core will be constant and the 

 current through R will therefore be constant. The veloci- 

 ties V and v' will then be such as to satisfy the condition. 



dQ ^^,dQ 



dL dl 



If the wire of resistance R were now to be replaced by 



one having a length 21 and a section 25, the current would 



remain unchanged. The potential or electrical pressure 



at the end which joins to the condenser core would remain 



unchanged. The current per unit cross-section and the 



drop in potential per unit length will be half as great as 



before. If we are to consider the amount of moving 



electric fluid contained in Ice of the wire to be the same 



as before, then v' will have been reduced to half its former 



do 

 value, and -^ will have been doubled. It would then 



require four times the time for a given element of the 

 fluid to traverse the resistance R, that was needed for the 

 wire of half the length. This involves an abrupt change 

 in the velocity of the corpuscles, at the point where the 

 cross-section s changes, in any circuit. Assume that a 

 conductor of different material in which k is greater and 

 I correspondingly greater replaces the one first 

 discussed. It seems possible that the molecular structure 

 might be such that v' might be either greater or less than 

 in the conductor which it replaced. 



