The Steam Engine Explained and Illustrated (Seventh Edition) / With an Account of Its Invention and Progressive Improvement, and Its Application to Navigation and Railways; Including Also a Memoir of Watt

by Dionysius Lardner

For brevity, let

e′ = a{	e	+ log.	1 + c	};
	e + c		e + c

∵ RVA(1 + m) = We′ − VA(b + r).(22.)

By solving this for VA, we obtain

VA =	We′	;
	R(1 + m) + b + r
∵ RVA =	We′R	.(23.)
	R(1 + m) + b + r

This quantity RVA, being the product of the resistance RA, of the load reduced to the surface of the piston, multiplied by the space through which the piston is moved, will be equal to the load itself multiplied by the space through which it is moved. This being, in fact, the useful effect of the engine, let it be expressed by U, and we shall have

U =	We′R	.(24.)
	R(1 + m) + b + r

Or by (22.),

U(1 + m) = We′ − VA(b + r).(25.)

The value of the useful effect obtained from these formulæ will be expressed in pounds, raised one foot per minute, W being the effective evaporation in cubic feet per minute, A the area of the piston in square feet, and V the space per minute through which it is moved, in feet.