Page:Popular Science Monthly Volume 12.djvu/272

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gested by Papin. It consists of two single-acting cylinders, r s, receiving steam alternately from the same steam-pipe through a "four-way-cock," and exhausting into the atmosphere. We find no evidence that this engine was ever built.

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Fig. 23.—Leupold's Papin Engine, 1720.

When, during the last century, the steam-engine had so far been perfected that the possibility of its application to other purposes than the elevation of water had become generally recognized, the problem of its adaptation to the propulsion of carriages was attacked by many engineers and inventors.

As early as 1759, Dr. Robison, who was at the time a graduate of the University of Glasgow, and an applicant for an assistant professorship there, and who had made the acquaintance of the instrument-maker, James Watt, when visiting the workshop, called the attention of the latter, who was probably then more ignorant of the principles of the steam-engine than was the young student, to the possibility of constructing a carriage to be driven by a steam-engine, thus, perhaps, setting in operation that train of thoughtful experiment which finally earned for Watt his splendid fame.

46. Watt, at a very early period, proposed to apply his engine to locomotion, and contemplated using either a non-condensing engine, or an air-surface condenser. He actually included the locomotive-engine in his patent of 1784, and his assistant, Murdoch, in the same year, made a working-model locomotive which was capable of running at a rapid rate.

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Fig. 24.—Murdoch's Model, 1784.

This model, now deposited in the Patent Museum, at South Kensington, London, had a flue-boiler, and a "grass-hopper" engine. Its steam-cylinder was three-quarters of an inch in diameter, and had two inches stroke of piston (Fig. 24). The driving-wheels were nine and a half inches in diameter. It is reported to have run six to eight miles an hour, its little driving-wheels making from two hundred to two hundred and seventy-five revolutions per minute.