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 ...

LOCOMIOTIVE ENGINES ON RAILWAYS. 201
the load which they are capable of transporting diminishes
in a very rapid ratio as the speed increases: thus, if 121 express the load which a horse is able to transport a given distance in a day, working at the rate of four miles an hour,
the same horse will not be able to transport more than the
load expressed by 64, the same distance, at 7 miles an hour;
and, at 10 miles an hour, the load which he can transport
will be reduced to 25. The most advantageous speed at
which a horse can work being 2 miles an hour, it is found
that, at this rate, working for 10 hours daily, he can transport 12 tons, on a level railway, a distance of 20 miles; so
that the whole effect of a day's work may be expressed by
240 tons carried I mile.
But this rate of transport is inapplicable to the purposes
of travelling; and therefore it becomes necessary, when
horses are the moving power, to have carriages for passengers distinct from those intended for the conveyance of
goods; so that the goods may be conveyed at that rate of speed
at which the whole effect of the horse will be the greatest
possible; while the passengers are conveyed at that speed
which, whatever the cost, is indispensably necessary. The
weight of an ordinary mail-coach is about two tons; and, on
a tolerably level turnpike road, it travels at the rate of 10
miles an hour. At this rate, the number of horses necessary to keep it constantly at work, including the spare horses
indispensably necessary to be kept at the several stages, is
computed at the rate of a horse per mile. Assuming the
distance between London and Birmingham at 100 miles, a
mail-coach running between these two places would require
100 horses; making the journey to and from Birmingham
daily. The performance, therefore, of a horse working at
this rate may be estimated at 2 tons carried 2 miles per day,
or 4 tons carried 1 mile in a day. The force of traction on
a good turnpike road is at least 20 times its amount on a
level railroad. It therefore follows, that the performance
of a horse on a railroad will be 20 times the amount of its
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