DIFFUSION. 639 



Hence the solution of the electrical problem leads to that of the other 

 two. For if V is the potential at any point, 



If E is the electric charge of the conductor, 



where the double integral is extended over the surface of the bulb, and dv 

 is an element of a normal to the surface. 



If H is the flow of heat in unit of time from the bulb, 



and if Q is the flow of aqueous vapour from the bulb, 



_ 



kjdv 



where k is the ratio of the pressure of aqueous vapour to its density. 

 If C is the electrical capacity of the bulb, E=CV iy 



The heat which leaves the bulb by radiation to external objects at tem- 

 perature may be written 



h=AB(0 1 -e tt ), 



where A is the surface of the bulb and R the coefficient of radiation of unit of 

 surface. 



When the temperature becomes constant 



AR 



This formula gives the result of the theory of diffusion, conduction, and 

 radiation in a still atmosphere. It differs from the formula of the convection 

 theory only by the factor in the last term. 



