24 g EIGHTEENTH CENTURY. PT. in. 



because there will always be an empty space or vacuum in 

 A to receive the steam as it rises. When the tap, c, is shut, 

 the steam in B will become very dense, and when it is 

 opened again, the greater part of the steam will rush out and 

 be cooled down in A, while B remains hot as before. 



FIG. 44. 

 Steam condensed in a separate vessel. 



A, Flask empty of air. B, Flask half-full of water and empty of air. c, Tap con- 

 necting the two bottles. D, Spirit-lamp keeping the water in B boiling. E, Basin 

 of ice cooling down the steam which passes into A. 



Watt's Engine. This was exactly the plan Watt 

 adopted in his steam-engine ; B answers to his cylinder 

 (Fig. 45), which could be kept always hot, and A to his 

 condenser, in which his steam was turned back into water. 

 We cannot follow out all the different steps of his inven- 

 tion, and must content ourselves with a rough description 

 of his engine after he had completed it, as shown in Fig. 45. 



In the first place you must notice that cold water is 

 kept flowing down from the tank A into B, and out through 

 the pipe c, so that the condenser standing inside B is kept 

 quite cold; and, secondly, I must tell you that the rods, i and 

 2, are so placed that when the engine-end of the lever-beam 

 is raised, as in the figure, the stopcocks a and c are open, 

 and b and d are shut ; and when that end of the beam falls, 

 b and d will be open, and a and c will be shut. 



