THE DKrOSTTION OF SMOKE AND DUST. 189 



the denser atmospliorc, than to rise in the ascending 

 current. 



Very interesting is it to note that tlio converse of what 

 has jast been mentioaed as taking pllaee with regard to a 

 hot body is true with regard to a cold body. To Lord 

 liayleigh is due the discovery that from a cold body a 

 stream of dnst-freo air descends. Both tliese jihcnomena 

 can be shown by means of the lantern in front of which a 

 glass chamber filled with smoke has been placed. A length 

 of platinum wii'e (placed on the base of the chamber) is 

 I'endered incandescent by the passage of an electric current 

 supplying a source of heat for the' first experiment ; and in 

 the second experiment iced water is passed through a metal 

 tube against the uppermost side of the chamber alrca-dy 

 tilled with lieated smoke. 



There is another process to which, smoke and dust can be 

 sabjocted with a view to their condetisation or deposition, 

 a process differing entirely from those already alluded to. 



Between thirty and forty years- ago an observer noted 

 what he termed the- "perfectly rttagical effect" produced 

 by an electrical discharge taking place in a body of smoke' 

 confined within a bell jar. He describes his jar as resting 

 in water in order to exclude the disturbing action of the 

 outside air, and he allowed small (|aautities of smoke to 

 onter through the top. Upon his electrical machine being 

 started, immediate condensation of the' smoke occurred. 



Hero the matter seemed to drop; M. Gnitard does not 

 appear to have made any farther investigation as to the 

 practical utility of his discovery for condensing objection- 

 able and waste smoke or fame. This experiment can be 

 performed more easily by an electrical machine such as that 

 desi'med by Mr. Wimshurst, than with the appliances which 

 were at M. Guiisard's command. If a pointed wire be led 



