The steam engine familiarly explained and illustrated; with an historical sketch of its invention and progressive improvement; its applications to navigation and railways; with plain maxims for railway speculators. By the Rev. Dionysius Lardner ... With additions and notes by James Renwick ...

282 THE STEAM ENGINE
water, and at the same time let another }, ilf ton of water be
supplied to the vessel w; the pressure beloOr the piston being
entirely removed, the atmospheric pressure will act above it
with undiminished force; and this force, amunting to one
ton, will draw up the vessel w, with its conten,'s. When the
piston descends, as it will do, to the bottom of the tube, the
ton of water contained in the vessel w will be raised through
two perpendicular feet."
Now, in this process it will be observed that the quantity
of steam consumed is not more than in the former case, viz.
the vapour produced by boiling one cubic inch of water.
Let us consider, however, the mechanical effect which has
resulted from it; half a ton of water has been allowed to
descend through one foot, while a ton has been raised through
two feet: deducting the force lost by the descent of half a
ton through one foot from the force obtained by the ascent
of one ton through the two feet, we obtain for the whole
mechanical effect one ton and a half raised through one foot;
for it is evident that half a ton has been raised from the
lowest point to which the vessel w descended one foot above
that point, and one ton has been raised through the other
foot, which is equivalent to one ton and a half through one
foot.
Comparing this with the effect produced in the first case,
where the steam was condensed without causing its expansion, it will be evident that there is an increase of 50 per
cent. upon the whole mechanical effect produced.
But this is not the limit of the increase of power by expansion. Instead of condensing the steam when the piston
had arrived at P", let a further quantity of water amounting
to one sixth of a ton be poured into the vessel wv, in addition to the half ton which it previously contained; the
Strictly speaking, the quantity of water supposed in these cases to be
placed in the vessel w would just balance the atmospheric pressure. A
slight preponderance must therefore be given to the piston, to produce the
motion.