Chap. 3.] Pump. 449 



cular height is that of the raifing pipe above the fur* 

 face of the water ; fo that when the raifing pipe is full, 

 the charge upon the pifton is equal to the weight of 

 a cylinder of water, the diameter of which is equal to 

 that of the pifton, and the height equal to that of the 

 raifing pipe above the furface of the water, whatever 

 may be the diameter of the mourning pipe j and this 

 charge or weight upon the pifton is eafily calculated, 

 when it is known that a cylinder of water of one foot 

 diameter and one foot high weighs about fifty-five 

 (French) pounds. 



It follows, therefore, that the weight of a column of 

 water is not diminimed by diminifhing the diameter 

 of the raifing pipe; but that, on the contrary, the re- 

 fiflance which ought to be overcome is even augmented 

 on account of the increafe of the friction, which is 

 more confiderable in fmall pipes than in large ones, 

 becaufe the relative furfaces augment as the diameters 

 diminiih. Thus, only for the expence, it would be 

 wrong to make, as is commonly done, the raifing pipe 

 fmaller than the body of the pump j on the contrary, 

 it would be better to conftruct it of a diameter greater 

 than that of the body of the pump, as the friction 

 would tje proportionably diminiflied. 



The forcing pump is compofed of the body of the 

 pump C D, (Plate VII Fig. 4.) flopped clofe at the 

 bottom, but entirely open above, and in which is a 

 pifton K, which only differs from that of the pump 

 already defcribed in this, that its fucker S is placed 

 at the bottom inftead of the top. This pifton, like 

 that of the pump juft mentioned, is put in action by 

 means of the lever Y X Z, which has its point of 

 fiipport in Z. The raifing pipe A O is placed at the 

 fide of the body of the pump, with which it commu- 

 nicates, and is furaiihed with a fucker s in its lower 



VOL. II. G g part, 



