612 TRANSACTIONS OF THE 



opinion. And, if the pressure is too low to work expansively, it 

 requires no acuteness to see the necessity of it; but if there be an 

 adequate pressure, an engine can draw a heavier train when cut- 

 ting off at half-stroke than wlien working with any larger admis- 

 sion; because the combined power of the engines is more equable 

 at this point than at a later point of cutting off, as may be seen by 

 a calculation of the leverage of the cranks, multiplied by the 

 pressure on the pistons. In working at half stroke with 100 lbs. 

 pressure, the combined power varies from 100 when one crank is 

 at the dead point, to 113 when both are at 45'^; but in working 

 at full stroke, with the pressure necessary for the same total 

 power, the combined power varies from 85 when the crank is at 

 the dead point, to 119 when both are art 45°. Now, the tractive 

 power of an engine, when in good order, is limited by the adhe- 

 sion of the wheels; and therefore the engine that with a given 

 total power, has a tendency of 113 to slip its wheels, will draw 

 more than one which, with the same total power, has a tendency 

 of 119 to slip its wheels. 



This equability is desirable in other cases, especially where it is 

 inconvenient to use heavy fly-wheels to equalize the power; and 

 it is to such a case that this valve piston is about to be applied. 



In favor of good distribution, I may add, that Mr. Corliss has 

 of late years been to several establishments that had engines by 

 builders of high reputation, and proposed to- furnish them with 

 new engines, take away their old ones, and accept half the saving 

 of fuel for three years, as payment for the exchange; and they 

 have, in most cases paid large sums to compound for the half of 

 the saving. The boilers have not been altered in the least, it 

 being the policy of Corliss to demonstrate that the engine alone 

 effected the saving. And this it did, solely by the superior dis- 

 tribution of steam, the chief excellence of which consists in the 

 quick cut-off, variable by the governor — that is, variable to suit 

 the exigencies of the work. The saving is effected by the princi- 

 ple of expansion, carried out boldly and vigorously, without 

 flinching from complexities that are greater than ever were pro- 

 posed to the English locomotive engineers. His maxim is, effi- 

 ciency first, then simplicity. Their maxim is, simplicity and 

 elegance first, then efficiency. li is, however, but just to add, 

 that a break-down on a railway is a matter to be avoided at a 

 great sacrifice and if a valve motion is likely to occasion it., it 

 is prudent to forego its advantages. 



I will now reply to the clinching argument of the link men, 

 namely the indicator diagrams, which, as they think, show that 



