the Weights of Atoms. 189 



molecules of solid matter in their thickness. The gases in 

 contact with the near faces of the porous plates would how- 

 ever, probably be somewhat approximately pure in practice 





G Q G 



R R R 



11 



with a practically realisable thinness of the porous plates, if 

 a, the distance between the two plates, is not less than five or 

 six centimetres and the scouring velocities moderately, but 

 not impracticably, great. According to the notation of § 37, 



