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piece V, have two other orifices at a and c, where the two 

 pipes- ^ b, fig. I, and c d, fig. 2. communicate with the two 

 canals in the piece of metal, being connected with them only 

 by the help of cement, that the barrel with its cock may be 

 occafionally disjoined from them : thus a feparate communica- 

 tion is formed between each of the pipes and the barrel. 



The pipe a 3, is only tV'^'^ of an inch in diameter, except at 

 its orifices which are widened ; one of them is connefled at b, 

 with a dudl formed in the piece of metal i, attached to the 

 box of leathers C, at the top of the barrel, which du(fl turn- 

 ing in an angle, without penetrating the box, opens into the 

 barrel : this pipe and du(fl are joined by a fimple application 

 of their orifices, which are made in the contiguous fides of 

 both, and the joint made air-tight by cement melted around 

 with a blow pipe ; and the fame might be eflPeded by the 

 preflTure of a fcrew clofing the furfaces, with oiled leather in- 

 terpofed. By this pipe, when the valve is fhut, and the key 

 of the cock fo placed that the communication of this pipe with 

 the bottom of the barrel is open, if the pifton be deprefiTed 

 from the top, all the air which is under it will be forced to 

 pafs, by this pipe, into thebarrel above the pifton ; and vice verfa, 

 if the pifton be elevated from the bottom ; fo that according 

 to the motion of the pifton, the air under or over it within 

 the barrel is made to change its place, and to circulate from 



the 



