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 ...

286 THE STEAM ENGINE.
It appears therefore from this reasoning, that when the
direct force of steam of greater pressure than the atmosphere
is used without condensation, the total mechanical effect is
always less than that produced by the condensation of atmospheric steam without expansion; but that the greater the
pressure under which the steam is produced, the less will be
the difference between these effects. In general, the proportion of the mechanical effect of high-pressure steam to the
effect produced by the condensation of atmospheric steam,
will be as the number of atmospheres expressing the pressure
of the steam to the same number increased by one. Thus,
if steam be produced under the pressure of six atmospheres,
the proportion of its effect to that of the condensation of
atmospheric steam will be as six to seven.
(133.) Another method of applying the power of steam
mechanically is, to combine its direct action with condensation, but without expansion.
The piston being, as before, loaded with one ton, the evaporation of the water will raise it through six perpendicular
inches, and the result so far will be equivalent to a ton raised
half a foot; but if the piston-rod be supposed also to act by a
chain or cord over a wheel, so as to pull a weight up, the
steam which has just raise-d the ton weight through six inches,
may be condensed, and the piston will descend with a force
of one ton into the vacuum thus produced, and another ton
may be thus raised through half a foot. The total mechanical
power thus yielded by the steam, adding to its direct action
its effect by condensation, will then be one ton raised through
one foot, being an effect exactly equal to that obtained by
the condensation of atmospheric steam.
If the piston be loaded with two tons, its direct action.
will, as we have shown, raise these two tons through four
inches, which is equivalent to two-thirds of a ton raised a
foot. By condensing this steam a ton weight may be raised
in the same manner', by the descent of the piston through a