These results must be understood to be subject to modifications in particular cases, and to be only average calculations. Different steam-engines, as well as different horses, varying in their performance to a considerable extent; and the roads on which horses work being in different states of perfection, and subject to different declivities, the performance must vary accordingly.
In the practical comparison, also, of the results of so powerful an agent as steam applied on railways, with so slight a power as that of horses on common roads, it must be considered that the great subdivision of load, and frequent times of starting, operate in favour of the performance of horses; inasmuch as it would oftener occur that engines capable of transporting enormous weights would start with loads inferior to their power, than would happen in the application of horse-power, where small loads may start at short intervals. This, in fact, constitutes a practical difficulty in the application of steam engines on railroads; and will, perhaps, for the present, limit their application to lines connecting places of great intercourse.
The most striking effect of steam power, applied on a railroad, is the extreme speed of transport which is attained by it; and it is the more remarkable, as this advantage never was foreseen before experience proved it. When the Liverpool and Manchester line was projected, the transport of heavy goods was the object chiefly contemplated; and although an intercourse in passengers was expected, it was not foreseen that this would be the greatest source of revenue to the proprietors. The calculations of future projectors will, therefore, be materially altered, and a great intercourse in passengers will be regarded as a necessary condition for the prosperity of such an undertaking.
If this advantage of speed be taken into account, horse-power can scarcely admit of any comparison whatever with steam-power on a railway. In the experiments which I have already detailed, it appears that a steam engine is capable of drawing 90 tons at the rate of about 20 miles an hour, and that it could transport that weight twice between Liverpool and Manchester in about 3 hours. Two hundred and seventy horses working in wagons would be necessary to transport the same load the same distance in a day. It may be objected, that this was an experiment performed under favourable circumstances, and that assistance was obtained at the difficult point of the inclined plane. In the ordinary performance, however, of the engines drawing merchandise, where great speed is not attempted, the rate of motion is not less than 15 miles an hour. In the trains which draw passengers, the chief difficulty of maintaining a great speed arises from the stoppages on the road to take up and let down passengers. There are two classes of carriages at present used: the first class stops but once, at a point half-way between Liverpool and Manchester, for the space of a few minutes. This class performs the thirty miles in an hour and a half, and sometimes in 1 hour and 10 minutes. On the level part of the road its common rate of motion is 27 miles an hour; and I have occasionally marked its rate, and found it above 30 miles an hour.