394 ?be Steam [Book VII. 



valves, one of which admits the fteam to pafs from 

 the infterftice into the inner -cylinder below the pifton, 

 or fhuts it out at pleaflire ; the other opens or fhuts 

 the end of a pipe, which leads to the condenfer. The 

 condenfer confiils of one or more pumps furnifhed 

 with clacks and buckets (nearly the lame as in com' 

 mon pumps) which are wrought by chains fattened 

 to the great working beam of the engine. The pipe, 

 which comes from the cylinder, is joined to the bottom 

 of thefe pumps, and the whole condenfer Hands im- 

 merfed in a ciftern of cold water fupplied by the engine. 

 The place of this ciftern is either within the houfe or 

 under the floor, between the cylinder and the lever 

 wall -, or without the houfe between that wall and the 

 engine (haft, as conveniency may require. The con- 

 denfer being exhaufted of air by blowing, and both 

 the cylinders being filled with fteam, the regulating 

 valve which admits the fteam into the inner cylinder 

 is fhut, and the other regulator which communicates 

 with the condenfer is opened, and the fteam rufhes 

 into the vacuum of the condenfer with violence ; but 

 there it comes into contact with the cold fides of the 

 pumps and pipes, and meets a jet of cold water, which 

 was opened at the fame time with the ex'hauftion regu- 

 lator ; thefe inftantly deprive it of its heat, and reduce 

 it to water; and the vacuum remaining perfect, more 

 fteam continues to rufh in, and be condenfed until the 

 inner cylinder is 'exhaufted. Then the fteam which 

 is above- the pifton, ceafing to be counteracted by 

 that which was below .it, acts upon the piftcn with its 

 whole elafticity, and farces it to defcend to the bottom 

 of the cylinder, and fo raifes the buckets of the pumps 

 which are hung to the other end of the beam. The 

 exhauftion regulator is now flint, and the fteam one 

 opened again, which, by letting in .the fteam, allows 



the 



