VI P15EFACE. 



we must add Ridwell, C'liattock. Beattie, Rtissel, Smithells, and Dawson), and the 

 papers will be foiiml without difficulty l>y consultinix recent numbers of the 

 riiiluisopliical Mayaziin. [MoieoNer, Vioi. Menitt, M. Bec(pieiel, and otlieis liave 

 given historical accounts of other phases of it. 



I may say in concluding, that coudensationally, Kelvin's nuclei and Aitken's 

 "dust " have not yet Ijeen quite supei"seded. The use of these somewhat antiquated 

 terms is therefore not merely dictated l)y convenience. Their appearance is in a 

 measure inevitable. To enqdoy them interchangeably with ' ion," would, in a 

 reseaich like the present, be hazardous. 



C. B. 



