It is conceded on all hands, that where speed is required in draught, the horse cannot compete with mechanical power. At three miles an hour, the horse is the most perfect locomotive machine; but if his velocity be increased to ten, most of his power is consumed in moving himself. The average exertion in each horse in a four-horse heavy coach, is calculated by the author of the excellent Treatise on Draught, appended to the work published on the Horse by the Society for the Diffusion of Useful Knowledge, not to be equal to a strain of more than 62-1/2 lbs., and at twelve miles an hour to be barely 40 lbs. It is therefore useless to rely oh horse-power to enable a neighbourhood to retain its advantages in competition with a railway. To meet this difficulty many ingenious men turned their attention to the possibility of inventing a steam-engine applicable to common roads; and although, in several instances, their experiments succeeded, and many of the difficulties were overcome, still it is not to be denied that, on the whole, macadamized roads are not adapted to locomotive machines. Even when the road is in the best possible condition, the concussion is found so great as materially to interfere with the action of the machinery; and if the road be slightly muddy, or sandy, or newly gravelled, the draught will be double, or even treble what it is on the same road when free from dirt or dust. The author of the _Treatise on Draught_, accordingly, concludes against the use of steam-carriages on common roads, chiefly on account of their want of uniform hardness and smoothness, and the consequent wear and tear of the coach. "Perfection in a road," he says, "would be a plain, level, hard surface;" and in another passage--"Hardness, therefore, and consequently the absence of dust and dirt, which is easily crushed or displaced, is the grand desideratum in roads." These opinions were published in 1831, and since that period the desideratum has been supplied. A method of preparing a road has been discovered, uniting all the qualities required for the perfection of a highway. We allude to the system recently introduced of paving a road with wood. On this smooth and hard surface a steam coach goes more easily than on iron rails, and the expense of laying it down is trifling in comparison.