THE STEAM-ENGINE. 



517 



nearly 15 tons, it follows that 15 cubic inches of water converted into steam 

 per minute, or 900 cubic inches per hour, will produce a mechanical force 

 equal to one horse. If, therefore, to 900 cubic inches be added the quantity 

 of water per hour necessary to move the engine itself, independently of its 

 load, we shall obtain the quantity of water per hour which must be supplied 

 by the boiler to the engine for each horse-power ; and this will be the same, 

 whatever may be the magnitude or proportions of the cylinder : 



