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 ...

YAME S WATT. 75
before the ascent could be completed. Here, then, was an
obvious and an extensive cause of the waste of heat. At
every descent of the piston, the cylinder should be cooled
below 100~; and at every ascent it should be again heated
to 210~. It, therefore, became a question whether the force
gained by the increased perfection of the vacuum was
adequate to the waste of fuel in producing the vacuum; and
it was found, on the whole, more profitable not to cool the
cylinder to so low a temperature, and consequently to work
with a very imperfect vacuum, and a diminished power.
Watt, therefore, found the engine involved in this dilemma: either much or little condensation-water must be used.
If much were used, the vacuum would be perfect; but then
the cylinder would be cooled, and would entail an extensive
waste of fuel in heating it. If little were used, a vapour
would remain, which would resist the descent of the piston,
and rob the atmosphere of a part of its power. The great
problem then pressed itself on his attention, to condense the
steam withtout cooling the cylinder.
From the small quantity of water in the form of steam
which filled the cylinder, and the large quantity of injected
water to which this communicated heat, Watt was led to
inquire what proportion the bulk of water in the liquid state
bore to its bulk in the vaporous state; and also what proportion subsisted between the heat which it contained in these
two states. He found by experiment that a cubic inch of
water formed about a cubic foot of steam; and that the cubic
foot of steam contained as much heat as would raise a cubic
inch of water to about 10000. (15.) This gave him some
surprise, as the thermometer indicated the same temperature,
2120, for both the steam and the water from which it was
raised. What then became of all the additional heat which
was contained in the steam, and not indicated by the thermometer? Watt concluded that this heat must be in some
way engaged in maintaining the water in its new form.
Struck with the singularity of this circumstance he corn