384 TRANSACTIONS OF THE 



condensation of the steam in the cylinder, before mak- 

 ing the returning stroke. 



The quantity of water evaporated with one bushel of 

 coal was, according to Mr Watt, rather more than 8 

 cubic feet, converting it into steam of 220°. It would 

 appear, from experiments in Cornwall, with engines on 

 the above principles, that there was an increase, at the 

 rate of 13.824 to .8, by each bushel of coal: 



The expansion of the steam in the cylinder, as alluded 

 to in No. 3, seems to have been the main cause of the 

 enormous advantages obtained by the extension and safe 

 application of this principle. By this, use is made of 

 a certain power that was before lost; for as, in the 

 steam engine, a certain quantity of fuel is required to 

 raise steam to a certain elasticity, so then if the steam be 

 allowed (after having moved the piston) to escape into 

 the atmosphere, without having acted expansively, the 

 fuel, which was consumed to raise it up to that elasticity, 

 will have been principally lost. Therefore it is saving, 

 and not gain, that thus results. 



The value of the advantages of clothing or covering 

 the boiler, &c., so variously estimated, is so effective, as 

 scarcely to permit the radiation from the boiler to be per- 

 ceptible, nor does the heat in the engine room materially 

 affect the boiler. It is considered that this improvement 

 has alone increased the duty of a hushel of coals ^ on the 

 average, per cent. 



Suspending the action of the piston, as described No. 

 5, produces a considerable increase of effects, as the 

 superior efficiency of engines for drawing water is de- 

 pendent upon their power being greatest at the com- 

 mencement of the lifting stroke, where more power is 

 necessary to overcome the vis inertise of the matter 

 raised, than to continue its motion. It is considered that 

 this tends to increase the duty at least one-sixth. 



