112 Mr Ritchie on anAh-pnmp without Artificial Valves. 



II. Phascolome (Geoff.) 

 Wombat of Bass. — Didelphis, Shaw. — Phascolome, St Hilaire, 

 Cuvier. 

 For the anatomy and natural history, see Anatomie Comparie, 

 and the Annales du Museum. 



On an Air-Pump without Artificial Valves. By William 

 Ritchie, A- M., Rector of Tain Academy. (Communicated 

 by the Author.) 



1 N the common construction of the air-pump, the valves are 

 very liable to be deranged, the repairing of which is attended 

 with much trouble and expence. In the following construction 

 no such derangement can possibly take place, which must of it- 

 self give this air-pump a decided advantage. 



The machine consists of a barrel shut at the lower end, and 

 having a small aperture at C, forming a free communication 

 with the receiver, F. (Plate I. fig. 8.) The piston D is solid, and 

 stuffed in the usual way. The piston rod works in a small stuf- 

 fing box at A, so as to render it completely air-tight. There is 

 a small aperture at E in the top of the barrel, to allow the air to 

 make its escape, when the piston is raised. This air-pump may 

 be worked in the usual way, or by the method of continued mo- 

 tion. In commencing the exhaustion of the receiver, the piston 

 is supposed to be below the small aperture at C. The piston is 

 then raised, and the air which occupied the barrel is forced out 

 through the aperture at E. The point of one of the fingers is 

 applied to the perforation, in the same manner as in playing the 

 German flute. The air easily passes by the finger, which, when 

 the piston begins to descend, shuts the opening, and completely 

 prevents the entrance of the external air. The piston is again 

 forced down below the opening C, the air in the receiver rushes 

 into the barrel, and is again expelled by the ascending piston. 



Since the air in the receiver has no valve to open by its elas- 

 ticity, it is obvious that there is no limit to the degree of exhaus- 

 tion, as in the common construction. 



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