steam expanded; thereby preventing that wasteful expenditure of heat, which was the necessary result of the old plan of condensing the steam in the working cylinder, by admitting a jet of cold water directly under the piston. In addition to this Watt surrounded the cylinder with a second casing to be filled with the surplus steam, for the purpose of preventing radiation of heat, and closed in the top (which in Newcomen's engine had been left open for the sake of the pressure of the atmosphere upon the piston) by putting a cover on, with a hole and stuffing box for the piston rod to slide through; a plan which enabled steam pressure to be used in place of atmospheric. Newcomen's engine, at this time used only for pumping out water in mines, thus became a true steam-engine of immense power, capable of being worked with economy, and of being turned to the various uses to which science has since applied it. For these great improvements a patent, dated January 5, 1769, was taken out by Watt and Dr. Roebuck, the founder of the Carron iron works, with whom Watt had become acquainted. Little, however, was done for some years in manufacturing engines on a large scale; Roebuck fell into difficulties, while Watt, harassed, depressed in spirits, and in want of money, was forced to obtain employment as a civil engineer and land-surveyor. Among the many works that he was engaged on in this capacity may be mentioned: the Crinan Canal, afterwards completed by Rennie; the deepening of the river Clyde; improvements in the harbours of Ayr, Port Glasgow, and Greenock; the building of bridges at Hamilton and Rutherglen; and lastly, surveying and estimating a line of canal between Fort William and Inverness, which was subsequently executed by Telford on a larger scale than was then proposed, under the name of the Caledonian Canal. In the latter half of the year 1773 Roebuck's affairs came to a crisis; and Watt, through the agency of Dr. Small, having been brought into relation with Mr. Boulton, a man possessing an intimate knowledge of business, with extended views and a liberal spirit of enterprise, an arrangement was entered into between them, and the firm of Boulton and Watt established at Soho. This was the turning point in Watt's fortunes; under the vigorous management of Boulton, his great invention at length began to be appreciated, and the saving of fuel was found to be nearly three-fourths of the quantity consumed by Newcomen's engine. In 1775 an extension of the original patent until the year 1800 was obtained. This gave a fresh stimulus to Watt's fertile brain, and resulted in patents being taken out, between the years 1781-1785, for the rotatory motion of the sun and planet wheels (the crank having been pirated by Wasbrough), _the expansive principle of working steam_; _the double engine_; _the parallel motion_; _the smokeless furnace_; _the float to regulate the supply of water into the boiler_; and _the governor_. At