288 Ritchie on a Double acting Air-Pump. 



modifications sustained by the latter; and in fact, it is well 

 known, that the capillary action experiences as much variation 

 in its effects from solids of different natures as from different 

 liquids. 



ON A DOUBLE-ACTING AIR-PUMP. 



By the Rev. WILLIAM RITCHIE, M.A., F.R.S., 

 Prof, of Nat. and Exper. Philos. Royal Institution. 



O EVERAL attempts have been made to construct double- 

 acting air-pumps; but from the fact that none of them are 

 in use, we may conclude that the practical difficulties attending 

 the construction of them were too great to bring them in com- 

 petition with those in common use. The following contrivance 

 appears to me sufficiently simple, and will obviously double 

 the power without adding materially to the expense, and with 

 very little additional friction. 



It consists of a barrel similar to Smeaton's air-pump, having 

 a solid piston, with a piston-rod working air-tight in a collar of 

 leather. The piston-rod has a hole drilled along its axis 



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the whole length of the barrel, for the purpose of receiv- 

 ing a brass rod, about the th of an inch in diameter. The 

 upper end of the rod is slit about an inch, and slightly opened, 

 so as to act as a spring by its friction in raising and depressing 



