NIPHER — OUTPUT OF THE XOX-CONDENSING STEAM ENGINE. 439 



For any constant boiler pressure there will be some definite 

 speed which will make ^5111' a maximum. The condition is 



L J/- 



Imposing this condition we have 

 (// + /") (/i^Po-\-B) = [A-\-Po-\-E-{-{5-]-c) «]2 



(II) 



The speed must be such that the boiler pressure required to drive 

 the unloaded engine at that speed, is a mean proportional be- 

 tween the constant boiler pressure under consideration, and the 

 boiler pressure required to start the unloaded engine, [see (7),] 

 all pressures being measured from vacuum. The load corres- 

 ponding to this maximum is of course found by imposing this 

 condition in (9) by the elimination of n. 



400 



600 



Equation (11) gives the relation between n and P' for a max- 

 imum output at any boiler pressure P' . It is the equation of 

 a parabola, which crosses the pressure axis at its intersection 

 with the line of zero load (7). The slope of this parabola is 



dP' 



dn 



= 2(3+c)+2 





(12) 



