﻿Nature of the Large Ions in the Air, 517 



The relation may be written 



exdpjo w p')\dd) p ' 



where m refers to the mass of the vapour. 

 Changing the variable this becomes 



If we now makejthe assumption that the density of the 

 adsorbed fluid is considerable compared with that of the sur- 

 rounding vapour, so that 1/p' may be neglected in comparison 

 with 1/cr', then taking p = a'R0, the equation becomes 



For water, making a similar assumption that 1/p may be 

 neglected in. comparison with 1/cr, we have 



X 1 ^P 



=m Fd§, 



l(dp\ 

 p\dO) 



so X p\d6, 



x = T7dPV' 



Y\dd) 

 Putting X'/X — l/n we may write 



ldp_ ±dP 

 p dO ~ nP dd ' 



If at two temperatures, 0j and 2 , corresponding values 

 are p 1 and P l5 p 2 and P 2 , then integrating we have 



©L-Vg 



That is, the mass of adsorbed fluid, and consequently the 

 mobility, will be the same at a temperature 6 2 as at a 

 temperature 6\ if the new vapour-pressure is 



P% 



n /P 2 



This equation, according to the assumptions which have 

 been made, is the formula for reducing the observed mobi- 

 lities to a common temperature, and thus affords a basis for 

 a discussion of the observations. 



