The rapid increase in the coal-trade of the Tyne about the beginning of the present century had the effect of stimulating the ingenuity of mechanics, and encouraging them to devise improved methods of transporting the coal from the pits to the shipping-places. From our introductory chapter, it will have been observed that the improvements which had thus far been effected were confined almost entirely to the road. The railway wagons still continued to be drawn by horses. By improving and flattening the tram-way, considerable economy in horse-power had been secured; but, unless some more effective method of mechanical traction could be devised, it was clear that railway improvement had almost reached its limits. Notwithstanding Trevithick's comparatively successful experiment with the first railway locomotive on the Merthyr Tydvil tram-road in 1804, described in a former chapter, he seems to have taken no farther steps to bring his invention into notice. He was probably discouraged by the breakage of the cast-iron plates, of which the road was formed, which were crushed under the load of his engine, and could not induce the owners of the line to relay it with better materials so as to give his locomotive a fair trial. An imaginary difficulty, also, seems to have tended, among other obstacles, to prevent the adoption of the locomotive, viz., the idea that, if a heavy weight were placed behind the engine, the "grip" or "bite" of its smooth wheels upon the equally smooth iron rail must necessarily be so slight that they would whirl round upon it, and, consequently, that the machine would not make any progress.[31] Hence Trevithick, in his patent, provided that the periphery of the driving-wheels should be made rough by the projection of bolts or cross-grooves, so that the adhesion of the wheels to the road might thereby be better secured. Trevithick himself does not seem to have erected another engine, but we gather from the evidence given by Mr. Rastrick in the committee on the Liverpool and Manchester Bill in 1825, that ten or twelve years before that time he had made an engine for Trevithick after his patent, and that the engine was exhibited in London. "A circular railroad was laid down," said Mr. Rastrick, "and it was stated that this engine was to run against a horse, and that which went a sufficient number of miles was to win." It is not known what afterward became of this engine. There were, however, at a much earlier period, several wealthy and enterprising men, both in Yorkshire and Northumberland, who were willing to give the locomotive a fair trial; and had Trevithick but possessed the requisite tenacity of purpose--had he not been too soon discouraged by partially successful experiments--he might have risen to both fame and fortune, not only as the inventor of the locomotive, but as the practical introducer of railway locomotion.