A 



JOURNAL 



OF 



NATURAL PHILOSOPHY, CHEMISTRY, 



AND 



THE ARTS. 



SUPPLEMENT to VOL. XII. 



ARTICLE I. 



A Defcription of an Air Pump upon a new Conjiruclion, By 

 Elizur Wright. Communicated, by Benj. Silliman, 

 Efq. Profejfor of Natural Philofophy, fyc. in Yale College, 

 Nezvhaven, America, 



UPON reading the improvements made in the air pump by The general im« 



Smeaton, Haas, Prince, Ruffe!, and Cuthbertfon, it occurred P? rfe ? ions of 



* the air pump 



to me that the end which they aimed at might in fome meafure explained, 

 be attained upon a principle that is different from either of thofe 

 by which their pumps have been conftructed It is well known 

 that in a common air pump the valve at the bottom of the bar- 

 rel depends upon the air in the receiver to open it. When the 

 air in the receiver is rarified to a certain degree, its fpring be- 

 comes too weak to overcome even the fmall refinance which 

 will arife from the weight of the valve, its ooheiion to the plate 

 occafioned by the oil, and its being ftretched tight over the 

 hole. Here the progreCs of exhauftion will flop. And this 

 would hold true, could it be poffible to produce a perfect va- 

 cuum in the barrel. But as the fame obftructions belong to the 

 pifton valve, together with the additional one arifing from the 

 prefiure of the external air upon it, and becauic the pifton can- 

 Vol. XII,— Supplement. X not 



