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

which expresses the whole mechanical effect per minute in pounds raised one foot.

If the steam be worked expansively, let it be cut off after the piston has moved through a part of the stroke expressed by e.

The volume of steam of the undiminished pressure P′ admitted per minute through the valve would then be

VA (e + c);

and the ratio of this volume to that of the water producing it being expressed by S′, we should have

S′ =	VA(e + c)	.
	W

The final volume into which this steam is subsequently expanded being VA(1 + c), its ratio to that of the water will be

S =	VA (1 + c)	.
	W

The pressure P′, till the steam is cut off, will be

P′ =	Wa	− b.(18.)
	VA(e + c)