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 ...

180 THE STEAM ENGINE.
instances tubes have been introduced, even to the number of
150, of 1 inch diameter. In the Meteor, 20 square feet
are exposed to radiation, and 139 to the contact of heated
air; in the Arrow, 20 square feet to radiation, and 145 to the
contact of heated air. The superior economy of fuel gained
by this means will be apparent by inspecting the following
table, which exhibits the consumption of fuel which was requisite to convey a ton weight a mile in each of four engines,
expressing also the rate of the motion:Average rate of Consumption of
Engines. speed in miles coke in pounds
per hour. per ton per mile.
No. 1. Rocket....... 14 2-41
2. Sanspareil.... 15 2'47
3. Phoenix...... 12 1'42
4. Arrow....... 12 1-25
(92.) Since the period at which the railway was opened
for the actual purposes of transport, the locomotive engines
have been in a state of progressive improvement. Scarcely
a month has passed without suggesting some change in the
details, by which fuel might be economized, the production
of steam rendered more rapid, the wear of the engine rendered slower, the proportionate strength of the different
parts improved, or some other desirable end obtained. The
consequence of this has been, that the particular engines to
which we have alluded, and others of the same class, without having, as it were, lived their natural life, or without
having been worn out by work, have been laid aside to give
place to others of improved powers. By the exposure of
the cylinders to the atmosphere in the Rocket, and engines
of a similar form, a great waste of heat was incurred, and it
was accordingly determined to remove them from the exterior of the boiler, and to place them within a casing immediately under the chimney: this chamber was necessarily
kept warm by its proximity to the end of the boiler, but
more by the current of heated air which constantly rushed