Chap, i.] Steam Engine. 3&5 



experiment, that the force of gunpowder is feeble, 

 when compared to that of rifing fceam. An hundred 

 and forty pounds of gunpowder blew up a weight of 

 thirty thoufand pounds ; but on the other hand, an t 

 hundred and forty pounds of water, converted by heat 

 into fleam, lifted a weight ,of feventy-feven thoufand 

 pounds, and would life a much greater, if there were 

 means of giving the (team greater heat with fafety; 

 for the hotter the fteam the greater is its force. 



The fteam engine, to which I had formerly occa- 

 fion fiightly to advert *, is a machine which may be, 

 and is occasionally applied' 1 to various mechanical pur- 

 poles where great force is required; but which has. 

 hitherto been principally ufed to clear mines from 

 water, and to raife water to a proper height for the 

 fupply of* cities. In thefe cafes, the expanfive power 

 of fteam is fo managed as to operate on immenfe 

 pumps, which could not conveniently be worked by 

 any other means. In order to give the reader a fu- 

 perficial idea of this machine, let us imagine a com- 

 mon pump prepared, and that we want to move the 

 Jiandle of this pump upwards by the force of fteam 

 only. In the firft place, let us fuppofe, that the handle 

 of the pump, or ibmething connected to it, was fo 

 contrived as to admit of being inferted in the barrel of 

 a gun, of fome cylindrical tube, fet upright over a 

 cauldron containing boiling water. Next let us fup- 

 pofe, that the fteam could be admitted into the tube, 

 through the touch- hole, and fo confined as to pafs 

 only by that way. Now as the fire begins to dilate the 

 fteam, a part of it will enter the tube by the touch- 

 hole, and this will prefs up the pump, which is fup- 

 pofed to be fo fitted to the tube as to prevent any part 



* See vol. i. p. li; 



VOL. II. G c of 



