Page:Inland Transit - Cundy - 1834.djvu/45

 in the resistance. It is therefore possible to assign such a velocity to a boat moved on a canal, that the resistance will exactly equal the resistance of the road to the carriage loaded with a weight equal to that of the boat.

Now, as the resistance of a canal below this limit will be less, while the resistance of the road will remain the same, it follows that at lower velocities the canal, cæteris paribus, will present less resistance to the force of traction. On the other hand, by increasing the speed beyond the limit assigned, the resistance of the canal increases faster than the square of the velocity, while the resistance of the road suffers no increase whatever. Hence, above this limit, the road will possess considerable advantage over a canal.

But besides this, the resistance of the road to the carriage increases in the direct proportion of the weight of the load; while the resistance of a canal to the boat is, comparatively speaking, but slightly increased by an increase of the weight. From these circumstances it is easy to infer, that very great weights, moved at very low velocities, require a less power of traction on canals than on common roads. But, on the other hand, when the speed is increased, or when the load is more moderate in its amount, the advantage of a common road prevails, and more especially with reference to the increase of speed. The greatest speed at which canals can be advantageously worked is from two to two and a half miles an hour. Now, we shall see hereafter, that when adequate moving powers are applied, even with very considerable weights, the speed attainable, without loss of advantage on roads, bears a large proportion to this.