Trevithick had, however, by means of his Pen-y-darran engine, in a great measure solved the problem of steam locomotion on railways. He had produced a compact engine, working on the high-pressure principle, capable of carrying fuel and water sufficient for a journey of considerable length, and of drawing loaded wagons at five and a half miles an hour. He had shown by his smooth-wheeled locomotive that the weight of the engine had given sufficient adhesion for the haulage of the load. He had discharged the steam into the chimney, though not for the purpose of increasing the draught, as he employed bellows for that purpose. It appears, however, that Trevithick's friend, Mr. Davies Gilbert, afterward President of the Royal Society, especially noticed the effect of discharging the waste steam into the chimney of the Pen-y-darran engine. He observed that when the engine moved, at each puff the fire brightened, while scarcely any visible steam or smoke came from the chimney. Mr. Gilbert published the result of his observations in "Nicholson's Journal" for September, 1805, and the attention of Mr. Nicholson, the editor, having thereby been called to the subject, he proceeded to make a series of experiments, the result of which was that in 1806 he took out a patent for a steam-blasting apparatus, by which he proposed to apply high-pressure steam to force along currents of air for various useful purposes, including the urging of furnace and other fires. It is thus obvious that the principle of the blast-pipe was known to both Gilbert and Nicholson at this early period; but it is somewhat remarkable that Trevithick himself should have remained skeptical as to its use, for as late as 1815 we find him taking out a patent, in which, among other improvements, he included a method of urging his fire by fanners, similar to a winnowing machine.