WATT, JAMES, the celebrated improver of the steam-engine, was the eldest son of James Watt, a merchant in Greenock, and was born on the 19th January 1736. lie received the rudiments of his education in his native town, and evinced an early partiality for mechanical pursuits. The bent of his mind led him to follow the profession of a ma thematical instrument make•,and in his 18th year he went to Loudon and remained a year under the tuition of a maker of mathematical instruments. The weak state of his health compelled him to return to Greenock, and after adding to his stock of practical acquirements by occasional visits to Glasgow, he resolved in. 1757 to establish himself in that city. The corporation, however, considered this step as subversive of their privileges, and the professors of the college gave him apartments within its pre cincts, as mathematical instrument maker to the university. In this situation he became acquainted with Dr. Black, and with Mr. Robison, who was then a student at the university.
Mr. Watt continued in the college till the year 1763, when he took up his residence in the town, previous to his marriage with his cousin, Miss Miller, which took place in the summer of 1764.
The subject of the steam-engine had frequently been discussed between him and Mr. Robison. who had suggested the practicability of its being applied as the moving power of wheel carriages. So early as 1761 or 1762, Mr. Watt made some experiments on the force of steam with a Pa pin's digester, and he had even constructed a small model consisting of an inverted syringe, the bottom of the rod of which was loaded with a weight. This model he wrought with strong steam, which was alternately admitted below the piston and let off into the atmos phere. He soon abandoned this construction on account of its imperfections, and in the manner which we have already fully detailed in our History of the Steam-Engine, he was gradually conducted to those great improvements upon the steam-engine which have immortalized his name.
In the year 1767 Mr. Watt surveyed the Forth and Clyde canal, hut as the bill was lost in parlia ment, he was enabled to superintend the execution of the Mcnkland canal, for which he had prepared the survey and estimates. Some time after he sur veyed for the Board of Trustees, the projected canal from Perth to Forfar, and at the desire of the commissioners of the annexed estates, he made a survey of the Crinan canal, which was afterwards executed by Mr. Rennie. • Mr. 1Vatt's reputation was now widely extended; and he was employed in a great variety of public which were then undertaken in Scotland; and he terminated his labours as an engineer with the survey or the Great Caledonian canal, since executed upon a more magnificent scale by Mr. Tellord.* Near the close of 1773, when Mr. Watt was en gaged in this last survey, he had the misfortune to lose his wife, by whom he had a son and a daughter. A short time after this event he seems to have ac cepted the invitation of Mr. Boulton to settle in England; and thus commenced that illustrious firm, the formation of which forms an epoch in the an nals of the arts of England.
In the year 1775 Mr. Watt married his second wife, Miss Alacgrigor, who still survives him, and from that period his time was occupied in those important arrangements regarding his patents, and in perfecting those inventions which we have already fully described.
While Mr. Watt was engaged in the survey of
the Crinan, and Gi1p, and Tarbet intended canals in 1772 and 1773, he employed two ingenious micro metors of his own invention for measuring distances, such as the breadth of arms of the sea, which could not be ascertained by the chain.
The following is Mr. Watt's own account and history of these inventions, as communicated by himself to Dr. Brewster in 1816.
The instrument I used was a telescope, with an object-glass of twelve inches, and an eye-glass of one and a-half inch focus, consequently magnifying eight times In the focus of the eye-glass there were placed two horizontal hairs, and one perpen dicular hair. The horizontal hairs were about one-tenth of an inch distant from each other, and as strictly parallel to each other, and at right angles to the perpendicular hair, as I could make them. A rod being placed upright at twenty chains dis tant, or any other convenient distance, on level ground, an index, consisting of a round disk of about eight inches diameter, painted white, with a horizontal line of one inch wide, painted on its horizontal diameter with vermilion, was fixed upon the rod about one foot from the ground, and another similar index was moved up and down the rod, until, upon looking through the telescope, the two horizontal hairs covered the red stripes on the lower and upper indexes; the telescope being turned on its axis until the perpendicular hair was parallel to the rod. The indexes being thus covered by the horizontal hairs accurately, the upper index was fixed to the rod, and the distance between the mid dle of the red stripes, on the two indexes, was di vided from the red into twenty parts, representing so many chains, which, with the instrument I used, were upon the rod about four and a-half inches each; and for distances exceeding five chains, this division into equal parts was sufficiently accurate; but for short distances it is not strictly so. I therefore lilted a pin at every chain, and holding up the rod at each of them, made the necessary cor rection: and as the focus of the object-glass is also affected by the distance, it is proper to adjust the eye-glass to it at every station. The divisions on the rod being marked with the number of chains they represent, it was only necessary to send an assistant with the rod to any place the distance of which was'wanted to be measured, and by signs to make him move the upper index up and down, until the two horizontal hairs covered the red stripes on the upper and lower indexes; the divisions on the rod then showed the distance, which I found could be ascertained to within less than one-hun dredth part of the whole distance, and with a higher magnifying power, could be done proportionally more accurate. The rod I commonly used was twelve feet long, and consequently could measure thirty chains; but by sliding another rod upon it, so as to lengthen it, I measured greater distances; and where still greater were wanted, I stretched a tape horizontally, and turning the telescope on its axis, made the single hair parallel to it, fixing an index at the end of the tape, and sliding the other along it, until it subtended the distance between the rivers. 1 then measured the subtended tape with the rod, and so ascertained the distance; but this expedient I rarely had recourse to, the distance 1 generally had occasion to measure rarely exceed ing half a mile, or forty chains.