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WAT series of sermons on the Assembly's Catechism; and "The Art of Divine Contentment." He died about 1690.—F.  WATSON,, brother of Caroline Watson, and like her celebrated for his mezzotint engravings after Reynolds and other contemporary portrait painters, was born in 1748. Among his best prints after Reynolds are those of Georgina, Countess Spencer; Mrs. Crewe; Mrs. Sheridan as St. Cecilia; and Bishop Newton. He also engraved some of Lely's Beauties of the Court of Charles II.; a Virgin and Child after Correggio; and Baucis and Philemon after Rembrandt. He died in 1781.—, another of the family, attained nearly equal celebrity by his prints, in the same manner, after Reynolds.—J. T—e.  WATSON,, an English physician and botanist, was born in 1715, and died on the 10th May, 1787. He devoted his attention in the first instance to pharmacy. He made important discoveries in regard to electricity, and prosecuted botany with vigour. In 1741 he was admitted a fellow of the Royal Society of London. He was also nominated by Sir Hans Sloane one of the conservators of the British museum. In 1745 the Royal Society awarded to him the Copley medal. In 1772 he was appointed to examine the powder magazine at Purfleet, and, in conjunction with Cavendish and Franklin, he made observations on lightning conductors. The universities of Halle and Wittemberg conferred on him the degree of doctor of medicine, and he entered into practice as a physician. He joined the College of Physicians, and he became one of the physicians of the Foundling hospital. He became vice-president of the Royal Society. In 1786 he had the honour of knighthood conferred upon him. To the Philosophical Transactions he communicated papers on mushrooms, on the properties of electricity, &c. He also published a few medical papers, one of them being on the best mode of inoculating for small-pox.—J. H. B.  WATT,, the great engineer and natural philosopher, and the chief inventor of the steam-engine, was born at Greenock in Scotland on the 19th of January, 1736, and died at Heathfield, near Birmingham, on the 19th of August, 1819. His father, James Watt, was a shipbuilder, engineer, ship-chandler, and merchant, and for many years a town-councillor and magistrate of Greenock. His grandfather was a teacher of mathematics and navigation in the same place, and long held the office of baron bailie or chief magistrate of the burgh of Carsdyke, now forming part of the town of Greenock. His great-grandfather is stated to have been a farmer or small landowner in Aberdeenshire, who lost his life and his whole possessions during the civil wars of the seventeenth century. The wife of James Watt the elder, and mother of the engineer, was Agnes Muirheid or Muirhead, a lady of an ancient and honourable Scottish family. Owing to the delicacy of his health in childhood much of his education was carried on at home; and he showed at an early age a taste for practical mechanics and experimental science, which his parents wisely indulged. Having already acquired some knowledge of mathematical instrument making, he went in 1755 to London, to perfect himself in that art, which he did by means of one year's apprenticeship under John Morgan of Finch Lane. In 1756 he returned to Scotland, and endeavoured to establish himself in business in Glasgow; but as he did not possess the privileges of a burgess of that city, he was prevented from engaging in trade within its bounds. Being thus excluded from the city of Glasgow, he took shelter in the university, whose members—being already aware of his abilities through the skill which he had shown in repairing and fitting up the instruments of their observatory—granted him in 1757 the use of a shop within the college, with the title of mathematical instrument maker to the university. Here he carried on business with moderate success until 1763, at first alone and afterwards in partnership with Mr. John Craig. The extensive range of his talents and information was at this time well-known in the university; and in consequence of this and of his amiable and social character, he enjoyed the intimate friendship of the most eminent of the professors, such as Black and Robison, and was often consulted by the students when they met with difficulties in the course of their studies. In 1763 he obtained a shop and a dwelling-house in Glasgow, and in 1764 he married a most excellent wife, whom he lost nine years afterwards. The extent of his scientific knowledge and mechanical skill enabled him, while established in Glasgow, to combine a variety of other pursuits with that of a mathematical instrument maker. Although deficient in a musical ear he made and repaired organs and other musical instruments; he invented and constructed many curious and useful machines; and he was extensively employed as a civil engineer. In conjunction with an uncle, John Watt, he made and published a Survey of the River and Firth of Clyde. He planned and executed the Monkland canal, which connects the Forth and Clyde canal with a district rich in coal and iron; the Crinan canal, which connects the Firth of Clyde with the Atlantic, and other works; and in 1773 he surveyed and reported on the projected Caledonian canal, afterwards executed by Telford. His attention was first directed to the steam-engine by Robison in 1759. The leading events in its previous history are stated in the articles of Alexandria,, and , which are here enumerated in the order of time. In 1761 and 1762 Watt made some experiments on a small model of a high-pressure or noncondensing steam-engine, composed of a digester for a boiler, and a syringe for a cylinder. In 1763 his mind was specially directed to the defects of the existing steam-engines, and the means of removing those defects, through his being charged with the repair of a working model belonging to the university of Glasgow, and since preserved as a most precious relic. That model represented Newcomen's atmospheric steam-engine, in which steam was introduced into the cylinder below the piston, while the piston was drawn up by the descent of a counterpoise; that steam was then condensed by the injection of a jet of cold water into the cylinder, and the piston was forced down by the excess of the pressure of the atmosphere above that of the uncondensed vapour. Watt perceived, while experimenting with this model, that much of the steam expended was evidently wasted without performing work, and that the condensation at the same time was imperfect. In seeking for the causes of those defects, and for their remedies, he set to work scientifically from the outset; and he was the first inquirer into the action of the steam-engine who ever did so. He studied the laws of the pressure of elastic fluids and the evaporating action of heat; he ascertained as accurately as he could, with the means of experimenting at his disposal, the expenditure of fuel in evaporating a given quantity of water, the quantity of cold water required in order to condense it again, and the relations between the temperature, pressure, and volume of the steam. Then reasoning from the data which he had thus obtained, he framed a body of principles expressing the conditions of the efficient and economic working of the steam-engine, which with very little addition or modification continue to be the foundation of its excellence to this day, and which cannot be expressed more clearly or concisely than in the words used by Watt himself in the specification of his patent of 1768-69:—"First, that vessel in which the powers of steam are to be employed to work the engine, which is called the cylinder, . . . must, during the whole time the engine is at work, be kept as hot as the steam that enters it; first, by inclosing it in a case of wood or any other materials that transmit heat slowly; secondly, by surrounding it with steam or other heated bodies; and thirdly, by suffering neither water nor any other substance colder than the steam to enter or touch it during that time. Secondly, in engines that are to be worked wholly or partially by the condensation of steam, the steam is to be condensed in vessels distinct from the . . . cylinders, although occasionally communicating with them. Thirdly, whatever air or other elastic vapour is not condensed by the cold of the condenser and may impede the working of the engine, is to be drawn out by means of pumps. .. Fourthly, I intend, in many cases, to employ the expansive force of steam to press on the pistons,. . . in the same manner in which the pressure of the atmosphere is now employed. . . . In cases where cold water cannot be had in plenty, the engines may be wrought by this force of steam only, by discharging the steam into the air after it has done its office." The fifth head of the specification relates to the use of oils and other lubricants for the piston, instead of water. The expense of obtaining a patent for Watt's invention in 1768-69, and commencing the working it out, was undertaken by Dr. John Roebuck (see ) on condition of his receiving two-thirds of the profit. But before any profit could be realized. Roebuck became unfortunately involved in pecuniary difficulties, which rendered it impossible for him to carry on the enterprise. In 1775 Roebuck's share in the patent was bought by Matthew Boulton of Birmingham, who immediately promoted the carrying out of the invention with the utmost 