It will be observed from these remarks that the doctor's notions were of the crudest sort, and, as he obviously contemplated but a modification of the Newcomen engine, then chiefly employed in pumping water from mines, the action of which was slow, clumsy, and expensive, the steam being condensed by injection of cold water, it is clear that, even though Boulton had taken up and prosecuted Darwin's idea, it could not have issued in a practicable or economical working locomotive. But, although Darwin himself--his time engrossed by his increasing medical practice--proceeded no farther with his scheme of a "fiery chariot," he succeeded in inflaming the mind of his young friend, Richard Lovell Edgeworth, who had settled for a time in his neighborhood, and induced him to direct his attention to the introduction of improved means of locomotion by steam. In a letter written by Dr. Small to Watt in 1768, we find him describing Edgeworth as "a gentleman of fortune, young, mechanical, and indefatigable, who has taken a resolution to move land and water carriages by steam, and has made considerable progress in the short space of time that he has devoted to the study." One of the first-fruits of Edgeworth's investigations was his paper "On Railroads," which he read before the Society of Arts in 1768, and for which he was awarded the society's gold medal. He there proposed that four iron railroads be laid down on one of the great roads out of London; two for carts and wagons, and two for light carriages and stage-coaches. The post-chaises and gentlemen's carriages might, he thought, be made to go at eight miles an hour, and the stage-coaches at six miles an hour, drawn by a single horse. He urged that such a method of transport would be attended with great economy of power and consequent cheapness. Many years later, in 1802, he published his views on the same subject in a more matured form. By that time Watt's steam-engine had come into general use, and he suggested that small stationary engines should be fixed along his proposed railroad, and made, by means of circulating chains, to draw the carriages along with a great diminution of horse labor and expense. It is creditable to Mr. Edgeworth's forethought that both the models proposed by him have since been adopted. Horse-traction of carriages on railways is now in general use in the towns of the United States; and omnibuses on the same principle regularly ply between the Place de la Concorde at Paris and St. Cloud, both being found highly convenient for the public, and profitable to the proprietors. The system of working railways by fixed engines was also regularly employed on some lines in the infancy of the railway system, though it has since fallen into disuse, in consequence of the increased power given to the modern locomotive, which enables it to surmount gradients formerly considered impracticable.