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 ...

238 THE STEAM ENGINE.
The bars upon which the fire rests are of solid metal; and
such is the intense heat to which they are subject, that, in
an engine constantly at work, it is unlikely that they will
last, without being renewed, more than about a week, if so
much. The draft is maintained in this engine by means of
a revolving fan worked by the engine. This, perhaps, is
one of the greatest defects as compared with other locomotives. The quantity of power requisite to work this bellows, and of which the engine is robbed, is very great. This
defect is so fatal, that I consider it is quite impossible that
the ingenious inventor can persevere in the use of it. Mr.
Hancock has abandoned the use of the cranks upon his
working axle, and has substituted an endless chain and ragwheels. This also appears to me defective, and a source by
which considerable power is lost. On the other hand, however, the weakness of the axle which is always produced by
cranks is avoided.
(111.) Mr. Nathaniel Ogle of Southampton obtained a
patent for a locomotive carriage, and worked it for some
time experimentally; but as his operations do not appear to
have been continued, I suppose he was unsuccessful in fulfilling those conditions, without which the machine could
not be worked with economy and profit. In his evidence
before a committee of the House of Commons, he has thus
described his contrivance:" The base of the boiler and the summit are composed of
cross pieces, cylindrical within and square without; there
are holes bored through these cross pieces, and inserted
through the whole is an air tube. The inner hole of the
lower surface, and the under hole of the upper surface, are
rather larger than the other-ones. Round the air tube is
placed a small cylinder, the collar of which fits round the
larger aperture on the inner surface of the lower frame, and
the under surface of the upper frame-work. These are both
drawn together by screws from the top; these cross pieces
are united by connecting pieces, the whole strongly bolted