, j 



DIFFUSION. 



The firet part of this factor is certainly less than unity, and probably 



boat 77. 



If the bulb is spherical and of radius r, A = 4trr* and C=r, so that the 



i _. 

 wood part is 



Hence, the larger the wet bulb, the greater will be the ratio of the effect 

 of radiation to that of conduction. If, on the other hand, the air is in motion, 

 this will increase both conduction and diffusion, so as to increase the ratio of 

 the first part to the second. By comparing actual observations of the dew- 

 point with Apjohn's formula, it has been found that the factor should l>e 

 somewhat greater than unity. According to our theory it oiight to be greater 

 if the bulb is larger, and smaller if there is much wind. 



Relation beluxen Diffusion and Electrolytic Conduction. 



Electrolysis (see separate article) is a molecular movement of the con- 

 stituents of a compound liquid in which, under the action of electromotive force, 

 one of the components travels in the positive and the other in the negative 

 direction, the flow of each component, when reckoned in electrochemical equiva- 

 lents, being in all cases numerically equal to the flow of electricity. 



Electrolysis resembles diffusion in being a molecular movement of two 

 currents in opposite directions through the same liquid ; but since the liquid 

 is of the same composition throughout, we cannot ascribe the currents to the 

 molecular agitation of a medium whose composition varies from one part to 

 another as in ordinary diffusion, but we must ascribe it to the action of the 

 electromotive force on particles having definite charges of electricity. 



The force, therefore, urging an electro-chemical equivalent of either com- 

 ponent, or ton, as it is called, in a given direction is numerically equal to the 

 electromotive force at a given point of the electrolyte, and is therefore com- 

 parable with any ordinary force. The resistance which prevents the current 

 from rising above a certain value is that arising from the encounters of the 

 molecules of the ion with other molecules as they struggle forward through 

 the liquid, and this depends on their relative velocity, and also on the nature 

 of the ion, and of the liquid through which it has to flow. 



