■±12 C. Barns — Behavior of Nuclei of Pure Water. 



the molecule proper is reached, tlie evidences of which are 

 now beyond question. In case of fog particles, when the 

 evaporation is reduced to extreme slowness, we may conceive 

 that all groups of molecules evaporate together at about the 

 same rate, and that therefore the residue, i. e. the persistent 

 water nuclei, are present in least amount. On the other hand, 

 when the evaporation is forced, or accelerated by the heat due 

 to compression, the more volatile constituents of the fog par- 

 ticles evaporate faster than the less volatile, and there is a 

 correspondingly greater residue of persistent water nuclei, 

 because of this concentration of the less volatile molecular 

 aggregates of water in each fog particle. It follows also that 

 relatively more persistent nuclei are obtained by the evapora- 

 tion of large fog particles than by the evaporation of small 

 particles, because a greater relative number of these droplets 

 would contain a sufficient number of the less volatile groups 

 to persist ; i. e., the opportunities for concentrating the less 

 volatile aggregates are enhanced. Finally it should never be 

 possible to replace all fog particles by the water nuclei derived 

 from them. All of these deductions are in keeping with the 

 experimental evidence as pointed out. 



