already alluded to, have hitherto excluded the use of the steam-engine upon canals, and, as far as I can now see, are likely to continue its exclusion, it is superfluous here to discuss the comparative merits of its power and that of horses. We must for the present regard the latter as the only power practically available upon canals for general use, and this power generally limited to a speed not exceeding 3 miles an hour.
It is not necessary here to notice particularly the application of a steam-engine upon great rivers and ship canals. There, it has no rival as a moving power, at any speed within twelve miles an hour, and its application is not restricted by any of those difficulties which attach to ordinary canals.
There are two methods by which the steam-engine may be applied to a great advantage to draw or impel carriages on At certain stations, placed at convenient intervals, there may be fixed steam-engines which act upon ropes extending along the road; and by working these ropes, may draw any wheel carriages which are attached to them. In this manner, carriages may be drawn from station to station, on a straight line of road upon which engines of this kind may be provided. The other method in general use consists in drawing the carriages by a travelling steam-engine, which impels itself together with its load. In the former method, large and powerful low-pressure, or condensing engines, are admissible; because they are stationary, their weight and complexity are not limited, and a sufficient supply of water may generally be provided at the several stations. The travelling steam-engines must, however, be light in their weight, small in their bulk, and simple in their structure. For this reason, a road.
