476 TRANSACTIONS OF THE AMERICAN INSTITUTE. 



Mr. Fisher opened, and stated the conditions under which steam could 

 be used expansively with profit; the main object should be to keep the 

 steam dry and hot, and to this end a heated jacket around the cylinder was 

 essential. 



Dr. Warren Rowell. — Mr. Cliairman, in order to show the theoretical and 

 practical value of the use of steam expansively, it will be necessary first 

 to show the theory as stated in several works on steam engines, some of 

 which have been edited and published by Bourne, Lardner, and others. In 

 the treatise on the steam engine, by the Artisan Club, edited by John 

 Bourne, London, 1849, I find the following statement at page 12: 



"The next improvement of Watts, that we have to mention, is his plan 

 of working steam expansively. This method consists in arresting the flow 

 of the steam into the cylinder, at a certain part of the stroke, leaving the 

 remainder of the stroke to be accomplished by the effort of the steam shut 

 up within the cylinder to occupy a large volume. The power of the engine 

 is, of course, diminished by this procedure, for the piston will descend 

 with less force when urged merely by the diminishing effort of the ex- 

 panding steam, than if pressed upon by steam entering at full pressure to 

 the end of the stroke. But steam, or in other words, fuel is saved in a 

 greater proportion than the power of the engine is diminished, so that the 

 expansive principle augments, and very materially too, the motive efiicacy 

 of the fuel. In fact, whatever power is obtained from the steam during 

 the act of expanding, is obtained without any expense, for if the steam 

 valve of the cylinder be closed when half the stroke of the piston is per- 

 formed, there will only be half the steam expended; but the steam shut 

 within the cylinder will press with a varying force on the piston to 

 the end of the strote, and the power thus realized is evidently got 

 without any expenditure of fuel. We think it probable that this improve- 

 ment originated in the desire merely to moderate the force of the single 

 acting engine towards the end of the stroke, and indeed Prof Robison, 

 who, from his intimacy with Watt, was probably well acquainted with the 

 circumstances of the discovery, virtually says that such was the case. * * * 

 The realization of an increase of power * * * by this expedient was an un- 

 expected result, but Watt immediately saw the importance of the principle, 

 which, in a letter from Glasgow, in 1169, to Dr. Small, of Birmingham, he 

 describes as doubling the effect of the steam. The distractions inci- 

 dental to his other pursuits, prevented him from carrying the principle of 

 expansion into practice till the year 1716, when it was tried upon the 

 engine at Soho, and in 1178 it was applied to an engine for raising water 

 erected at Shadwell. In 1782 Watt took out a patent for improvements 

 in the steam engine, in which the principle of expansion formed a promi- 

 nent feature; having been, probably, instigated to that act by a patent 

 taken out by Hornblower, in 1781, for a metliod of using the steam twice 

 over, by first impelling a small piston, by high pressure on Leopold's 

 method, and then using it on a large piston by the method of condensation. 

 This scheme is identical in principle with the plan of using the steam 

 expansively, for it is obvious that the same power will be given out by a 

 cylinder, whether it be tall and narrow or short and wide, provided its 

 capacity remains the same. 



