Page:A biographical dictionary of eminent Scotsmen, vol 7.djvu/292

428 six contrivances for regulating the motion—double acting engine—two cylinders—parallel motion, by rack and sector—semirotative engine—and steam wheel. A third was granted in 1784, for a rotative engine parallel motions portable engine and steam carriage working hammers improved hand gear, and new method of working the valves. The most important of these inventions are, the double acting engine, in which steam is admitted both below and above the piston alternately, steam pressure being thus employed to press on each side of the piston, while a vacuum was formed over the other. By this contrivance, he was enabled to double the power of the engine, without increasing the dimensions of the cylinder. To the complete effecting of this, he was obliged to cause the piston rod to move through a stuffing box at the top of the cylinder; a contrivance, it must be stated, which had been some years previous applied by Smeaton, in the construction of pumps. Simple as these additions may at first appear, they were, nevertheless, followed by many great advantages. They increased the uniformity of motion, and at the same time diminished the extent of cooling surface, the size of boiler, and the weight and magnitude of the whole machinery. Another vast improvement involved in these patents, is the expansive engine in which the steam was let fully in, at the beginning of the stroke, and the valves shut, when the piston had advanced through a part of its progress, the rest being completed by the expansion of the steam; which arrangement greatly increases the power. This engine was included in the patent for 1782; though Mr Hornblower had published something of the same nature the year before. But an engine on the expansive principle was erected by Walt at Shad well iron works in 1778, and even two years before expansive engines had been manufactured at Soho; facts which secure to Watt the honour of the priority of discovery. That ingenious combination of levers which guided the piston rod, and is called the parallel motion, was secured by patent of 1784, and remains to this day unsurpassed as a beautifully simple mechanical contrivance.

In 1785, a patent was granted to Mr Watt for a new method of constructing furnaces, and the consumption of smoke. He likewise applied to the steam engine the governor, or conical pendulum, the steam and condension gauges, and the indicator. About the same time, in consequence of the delay and expense attendant on the numerous experiments towards the perfection of this vast creator and distributor of power, he found it necessary to apply to parliament for an extension of his patent, which was granted to the end of the eighteenth century. By this grant, the proprietors of the Soho foundery were enabled speedily to realize a great fortune.

In the winter of the year 1786, the subject of this memoir, together with his able and active partner, went to Paris, at the solicitation of the French government, in order to improve the method of raising water at Marley. Here Mr Watt met with most of the eminent men of science, who at that time adorned the French metropolis; and among the rest, the celebrated chemist, Berthollet. The French philosopher had discovered, in 1785, the bleaching properties of chlorine, and communicated the fact to Mr Watt, with the power of patenting the invention in England. This Mr Watt modestly declined doing, on the ground that he was not the author of the discovery. Mr Watt saw the value of this new process, and communicated the matter, through the course of the following year, to his father-in-law, Mr M'Gregor, who at that time carried on a large bleaching establishment in the vicinity of Glasgow. He sent an account of the process, together with some of the bleaching liquor, in March, 1787; and the process of bleaching by the new method was immediately com- menced at MrM'Gregor's field, and five hundred pieces were speedily executed