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 ...

250 THE STEAM ENGINE.
increased durability of the engines; the prevention of accidents through carelessness, or otherwise, arising from the
condenser and air-pump becoming choked with injection
water; and the additional security against the boilers being
burnt in consequence of the water being suffered to get too
low. But the greatest advantages, compared with which
they consider all others to be of secondary importance, are
the increased durability of the boilers and the saving of
fuel.
About sixteen engines, built either wholly upon Mr. Hall's
principle, or having his condenser attached to them, have
now (October, 1835) been working in different parts of
England, and on board different vessels for various periods,
from three years to three months; and it appears from the
concurrent testimony of the proprietors and managers of
them, that they are attended with' all the advantages which
the patentee engaged for. The part of the contrivance the
performance of which would have appeared most doubtful
would have been the maintenance of a sufficiently good
vacuum in the condenser, in the absence of the usual method
of condensation by the injection of cold water; nevertheless
it appears that a better vacuum is sustained in these engines
than in the ordinary engines which condense by jet. The
barometer gauge varies from 29 to 29' inches, and in some
eases comes up to 30 inches, according to the state of the
barometer: this is a vacuum very nearly perfect, and indeed
may be said to be so for all practical purposes. The Prince
Liewellyn and the ~dir steam packets, belonging to the St.
George Steam Packet Company, have worked such a pair
of these engines for about a year. The City of London
steam packet, the property of the General Steam Navigation
Company, has been furnished with two fifty-horse engines,
and has worked them during the same period. In all cases
the boilers have been found perfectly free from scale or
incrustation; and the deposite is either absolutely nothing or
very trifling, requiring the boiler to he swept about once in