453 ne Fire [Book VII. 



a icrevv ferule, intended to receive a nut, by means of 

 which the leathern pipe is joined to this end of the 

 engine, and which ferves inftead of the raifing pipe 

 in the common forcing pump. All this apparatus is 

 placed (as may be feen in Plate IX. Fig. 2.) upon a 

 box or cafe N O lined with lead, which contains the 

 water. The crofs bar Q^fupports the upper end F 

 (Fig. i.) of the body of the pump, which, for that 

 purpcfe, is of a Imaller diameter than the reft ; and 

 the lid L (Fig. 2.) of the box has an aperture in the 

 middle, to admit the afpiration pipe H T to pafs 

 through it. 



From this explanation it will be evident, that if the 

 pifton M is raifed up by putting the lever Y X Z in 

 the fituation y n Z, the fucker s and the valve ^, placed 

 at C, will be cJofed by the preffure of the exterior air. 

 This fame prefiure, exercifmg its force upon the fur- 

 face of the water V V, obliges it to pafs into the body 

 of the pump by raifing up the fucker S. It then acts 

 #s a fucking pump ; but when the pifton M is lowered, 

 its preffure clofes the fucker S, and opens the valve 

 which is at C ; the water then pafTes, not only into the 

 leathern pipe a b d, (Fig. 2.) by raifing up the fucker s 

 (Fig. i.) but alfo into the fpace between the body of 

 the pump and the pipe which inclofes it, by rifing 

 towards I K, and compreffes the air which is confined 

 there. Immediately after the pifton M is raifed 

 again, that air, being no longer compreffed, unfolds 

 itfelf by its elafticity, acts upon the water which is be^ 

 tween the body of the pump and the pipe which in- 

 ciofed it, and forces it alfo into the leathern pipe, fo 

 that when the pifton is lowered, the water is forced by 

 the pifton itfelf, and when it is raifed, the water is 

 forced by the elafticity of the air, which furnifhes a 

 continued ftream, though the pump has only one body 

 or principal tube, 



