the power may be increased in a greater ratio than the weight; but, with our limited knowledge of the application of Steam, and with the present formation of the Public Roads, the point will be very soon attained, when the advantage of increased power will be counterbalanced by the difficulties attendant on the increased weight of the engines.
The weight of the Steam Carriages at present in use varies from 53 to 80 cwt.; but it must be recollected that they are mere models; they were made with attention to strength only, to bear the uncertain strain to which they would be exposed in the course of experiments, and a very considerable diminution of weight may be anticipated.
The weight drawn, at the rate of ten miles per hour, by Mr. Gurney's Engine, has not, on any extent of road, exceeded the weight of the drawing Carriage; nor is it likely, with the difficulties to be encountered on the present line of road, from their quality and the numerous ascents, that the weight drawn will be in excess of the strength of the roads. The immense quantity of spare power required to surmount the different degrees of resistance likely to occur, would render the Engine too unmanageable. This will appear evident from the force of traction required to draw a Waggon over the Holyhead and Shrewsbury road, which varied from 40 to upwards of 300lbs.
In considering the effect on roads, we must not overlook one peculiarity, in which they have a great advantage over other Carriages. In Coaches drawn by horses, the power being without the machine to be moved, it becomes an object of the greatest importance to give as much effect as possible to the power, by diminishing the resistance, arising from the friction of the wheels upon the surface of the road. For this purpose, the proprietors of Coaches and Waggons have adopted every possible contrivance, so to reduce the tires of their wheels, that a very small portion of them may press on the road; in some Coaches they are made circular in their cross section, so that the entire weight of the Carriage presses on
