142 VOYAGE TO MADAOAfiCAK, 



water^ which ifTues from the boiler, intro* 

 duces itfelf under the pifton of the pump, 

 by the power of its expanfive force* When 

 the pifton is at its higheft degree, of eleva- 

 tion, the communication between the /team 

 that rifes from the boiler, and the cylinder 

 or body of the pump, is intercepted. At the 

 fame time the injedion of cold water occa- 

 fions a vacuum, by fuddenly condenfing 

 the fteara with which the body of the cy- 

 linder is filled^ and the weight of the exter- 

 nal air immediately forces the pifton to 

 defcend* It is well known, that the valves 

 and cocks, which open and £hut the com- 

 munication between the fteam and the in- 

 jected water, are always put in motion by 

 the movement of the pillon. The Mar- 

 quis of Worceller, in 1663, was the firft, 

 who, by the means of fteam, was able to 

 raife water to a great heiglit on alter- 

 Dately turning two cocks. After this difco- 



very, 



