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 ...

58 THE STEAM ENGINE.
engine is presented in fig. 9. The different parts already
described will easily be recognised, being marked with the
same letters as in figs. 6, 7.
(33.) In order duly to appreciate the value of improvements, it is necessary first to perceive the defects which
these improvements are designed to remove. Savery's
steam engine, considering how little was known of the
value and properties of steam, and how low the general
standard of mechanical knowledge was in his day, is certainly highly creditable to his genius. Nevertheless it had
very considerable defects, and was finally found to be inefficient for the most important purposes to which he proposed
applying it.
At the time of this invention, the mines in England had
greatly increased in depth, and the process of draining them
had become both expensive and difficult; so much so, that
it was found in many instances that their produce did not
cover the cost of workin'g them. The drainage of these
mines was the most important purpose to which Savery
proposed to apply his steam engine.
It has been already stated that the pressure of the atmosphere amounts to about 15 lbs. (3) on every square inch.
Now, a column of water, whose base is one square inch, and
whose height is 34 feet, weighs about 15lbs. If we suppose
that a perfect vacuum were produced in the steam vessels v
v' (fig. 8) by condensation, the atmospheric pressure on I.
would fail to force up the water, if the height of the top of
these vessels exceeded 34 feet. It is plain, therefore, that
the engine cannot be more than 34 feet above the water
which it is intended to elevate. But in fact it cannot be so
much; for the vacuum produced in the steam vessels v v
is never perfect. Water, when not submitted to the pressure
adopt an arrangement of parts somewhat different from that of the real machine
When once the nature and principles on which the machine acts are well under
stood, the reader will find no difficulty in transferring every part to its propet
place, which is represented in the perspective drawings.