Symington and Sadler, "the hunters of shadows" referred to by Watt, did little to advance the question. Of Sadler we know nothing beyond that in 1786 he was making experiments as to the application of steam-power to the driving of wheel-carriages. This came to the knowledge of Boulton and Watt, who gave him notice, on the 4th of July of the same year, that "the sole privilege of making steam-engines by the elastic force of steam acting on a piston, with or without condensation, had been granted to Mr. Watt by Act of Parliament, and also that among other improvements and applications of his principle he hath particularly specified the application of steam-engines for driving wheel carriages in a patent which he took out in the year 1784." They accordingly cautioned him against proceeding farther in the matter; and as we hear no more of Sadler's steam-carriage, it is probable that the notice had its effect. The name of William Symington is better known in connection with the history of steam locomotion by sea. He was born at Leadhills, in Scotland, in 1763. His father was a practical mechanic, who superintended the engines and machinery of the Mining Company at Wanlockhead, where one of Boulton and Watt's pumping-engines was at work. Young Symington was of an ingenious turn of mind from his boyhood, and at an early period he seems to have conceived the idea of employing the steam-engine to drive wheel-carriages. His father and he worked together, and by the year 1786, when the son was only twenty-three years of age, they succeeded in completing a working model of a road locomotive. Mr. Meason, the manager of the mine, was so much pleased with the model, the merit of which principally belonged to young Symington, that he sent him to Edinburg for the purpose of exhibiting it before the scientific gentlemen of that city, in the hope that it might lead, in some way, to his future advancement in life. Mr. Meason also allowed the model to be exhibited at his own house there, and he invited many gentlemen of distinction to inspect it. [Illustration: SYMINGTON'S MODEL STEAM-CARRIAGE, 1786.]