386 fbe Steam [Book VII. 



of the {learn from efcaping. In this way the pump 

 handle would be driven quite out at the mouth of the 

 tube, but let us imagine, that before this can happen 

 valve is opened, which allows a fmall quantity of cold 

 water to be fpouted into the tube, which effectually 

 and inftantaneoufly deflroys, or, more properly, con*. 

 denfes the fleam. The tube being now left empty, 

 there is nothing to counteract the preflure of the at- 

 mofphere, which again forces down the handle into 

 the tube, into which no fleam is permitted to enter, on 

 account of a valve which now flops the touch- hole 

 below; but when the handle is thus prefled down, the 

 valve below is again opened, and new fleam entering 

 again prefTes the handle upwards ; when the handle 

 comes near the top, the fleam is again cooled and 

 condenfed as before, and the handle is again prefled 

 down by the weight of the atmofphere. In this man- 

 ner it is alternately driven upwards and downwards by 

 the expanfive power of the fleam and the prefiiire of 

 the external air, and works the pump with unwearied 

 affiduity. 



, .Though the principle however, is plain, the ma- 

 chinery is complex in the fleam engine j but the 

 annexed plate IV. will probably render it tolerably 

 intelligible. 



In fig. I. A feprefents the fire-place under the 

 boiler, for the boiling of the water, and the afh- 

 hole below it. 



B, the boiler, filled with water about three feet above 

 the bottom, made of iron plates. 



C 3 the fleam pipe, through which the fleam pafTes 

 from the boiler into the receiver. 



D, the receiver, a clofe iron veflel, in which is the 

 regulator or fleam-cock, which opens sfticf {huts the 

 hole of communication at each flroke. 



E, the 



