The Life of James Watt

"dispensed with in the others." On the 21st of October, 1784, he writes:-"The new central perpendicular motion answers beyond expectation, and does not make the shadow "of a noise." *

The manufacturing profits which Boulton and Watt stipulated to receive from the Cornish miners who used their engines, were at first one-third of the savings of fuel made by each engine, when compared with a common one burning the same kind of coal, to be paid annually or half-yearly, with an option of redemption at ten years' purchase. In point of fact, they did not receive nearly that proportion; but still, such was the agreement made, and such, had it been honestly adhered to by the miners, would have been the amount paid. It therefore became essential to ascertain the exact number of strokes made by each engine during any given time, in a way that should be independent of all possibility of deception or interference by those employed about the engine. This object was fully attained by Mr. Watt's invention of his "Counter;" a neat piece of clockwork containing a pendulum, a train of wheels with an escapement, and several dials like those of watches graduated with numbers, and each with its index: the first index marking, on its own dial, tens; the next, hundreds; the next, thousands; and so on in the same ratio up to any required amount. Eight dials, with their respective indices, were found sufficient to count the strokes of an engine going constantly, day and night, for a year. The pendulum was fixed horizontally and transversely across the width of the beam, with the axes of the wheels vertical, while the beam was horizontal, and the piston at the middle of a stroke: thus, at every inclination of the beam either downwards or upwards, the pendulum moved across the width of the box, and, by the vibratory movement of the pendulum and pallets, the escapement wheel was turned one tooth for each complete stroke of

*The specification of the patent of April 28th, 1784, is printed in the Mechanical Inventions of James 'Watt,' 1854, vol. iii., pp. 88 to 114;

and the relative drawings are engraved on Plates XX., XXI., XXII., XXIII., XXIV., XXV., XXVI., XXVII., and XXVIII.

the piston. And the whole work of the counter being enclosed in a box which was fastened by screws from within on the great beam of the engine and then locked, was inaccessible except to those in possession of the key.

Some other equally ingenious inventions, introduced by Mr. Watt at various periods, very greatly increased the utility of the engine; and although it would be vain here to attempt to give anything like a complete enumeration of his almost endless contrivances connected with the details of the different parts, yet we may mention especially, as among the leading improvements, the Throttle-Valve, the application of the Governor, the Barometer or Float, the Steam-Gauge, and the Indicator.

The great use of the Throttle-Valve was to regulate the speed of the rotative engines for mill-work, a matter essential to their application to cotton-spinning and many other like purposes; it is described by Mr. Watt as "a circular plate of metal, having a spindle fixed across its diameter, the plate being accurately fitted to an aperture in a metal ring of "some thickness, through the edgeway of which the spindle " is fitted steam-tight, and the ring fixed between the two "flanches of the joint of the steam-pipe which is next to the cylinder. One end of the spindle, which has a square upon "it, comes through the ring, and has a spanner fixed upon it, "by which it can be turned in either direction. When the "valve is parallel to the outsides of the ring, it shuts the opening nearly perfectly; but when its plane lies at an angle to the ring, it admits more or less steam according to "the degree it has opened; consequently the piston is acted "upon with more or less force. For many purposes engines "are thus regulated by hand at the pleasure of the attendant; but where a regular velocity is required, other means "must be applied to open and shut it, without any attention on the part of those who have the care of it.

"For this purpose Mr. Watt had various methods, but at "last fixed upon what he calls the Governor, consisting of a "perpendicular axis, turned by the engine: to a joint near "the top of this axis are suspended two iron rods carrying

"heavy balls of metal at their lower ends, in the nature of pendulums. When this axis is put in motion by the engine, "the balls recede from the perpendicular by the centrifugal "force, and, by means of a combination of levers fixed to their upper end, raise the end of a lever which acts upon the spanner of the throttle-valve, and shuts it more or less according to the speed of the engine, so that as the velocity augments, the valve is shut, until the speed of the engine "and the opening of the valve come to a maximum, and "balance each other. The application of the centrifugal principle was not a new invention, but had been applied by "others to the regulation of water and wind mills, and other things; but Mr. Watt improved the mechanism by which it "acted upon the machines, and adapted it to his engines."

Such," says M. Arago,—in describing Mr. Watt's application to the steam-engine of this "governor," or "regulator by centrifugal force,"-" was its efficacy, that there was to "be seen at Manchester a few years ago, in the cotton-mill "of Mr. Lee, a man of great mechanical talents, a clock "which was set in motion by the steam-engine used in the "work, and which marked time very well, even beside a "common pendulum clock."*

"From the beginning, Mr. Watt applied a gauge to show "the height of the water in his little boiler; which consisted "of a glass tube communicating at the lower end with the "water in the boiler, and at the upper end with the steam "contained in it. This gauge was of great use in his experiments, but in practice other methods are adopted. He has "always used a barometer to indicate the degree of exhaus"tion in his engines. Sometimes that instrument is, as “usual, a glass tube 33 or 34 inches long, immersed at "bottom in a cistern of mercury, and at top communicating "by means of a small pipe and cock with the condenser. "The oscillations are in a great degree prevented by throttling the passage for the steam by means of the cock.

"But, as glass tubes were liable to be broken by the work"men, barometers were made of iron tubes, in the form of "inverted syphons, one leg about half the length of the "other; to the upper end of the long leg a pipe and cock "were joined, which communicated with the condenser; a proper quantity of mercury was poured into the short leg " of the syphon, and naturally stood level in the two legs; a light Float with a slender stem was placed in the short leg, "and a scale, divided into half-inches, applied to it, which, (as by the exhaustion the mercury rose as much in the long leg as it fell in the short one), represented inches on the "common barometer.

"The Steam-Gauge is a short glass tube with its lower end "immersed in a cistern of mercury, which is placed within an iron box screwed to the boiler steam-pipe, or to some "other part communicating freely with the steam, which, pressing on the surface of the mercury in the cistern, raises "the mercury in the tube, (which is open to the air at the upper end), and its altitude serves to show the elastic power "of the steam over that of the atmosphere.

"These instruments are of great use when they are kept "in order, in showing the superintendent the state of the engine; but slovenly engine-tenders are but too apt to put "them out of order, or to suffer them to be so. It is the "interest, however, of every owner of an engine to see that they, as well as all other parts of the engine, are kept in "order.

"The barometer being adapted only to ascertain the degree of exhaustion in the condenser where its variations "were small, the vibrations of the mercury rendered it very "difficult, if not impracticable, to ascertain the state of the "exhaustion of the cylinder at the different periods of the "stroke of the engine; it became therefore necessary to con"trive an instrument for that purpose that should be less subject to vibration, and should show nearly the degree of "exhaustion in the cylinder at all periods. The following "instrument, called the Indicator, is found to answer the end sufficiently. A cylinder about an inch diameter, and six

"inches long, exceedingly truly bored, has a solid piston "accurately fitted to it, so as to slide easy by the help of some "oil; the stem of the piston is guided in the direction of the "axis of the cylinder, so that it may not be subject to jam, "or cause friction in any part of its motion. The bottom of “this cylinder has a cock and small pipe joined to it, which, having a conical end, may be inserted in a hole drilled in "the cylinder of the engine near one of the ends, so that, by "opening the small cock, a communication may be effected "between the inside of the cylinder and the indicator.

"The cylinder of the indicator is fastened upon a wooden or "metal frame, more than twice its own length; one end of a "spiral steel spring, like that of a spring steelyard, is attached "to the upper part of the frame, and the other end of the "spring is attached to the upper end of the piston-rod of the "indicator. The spring is made of such a strength, that "when the cylinder of the indicator is perfectly exhausted, "the pressure of the atmosphere may force its piston down “within an inch of its bottom. An index being fixed to the top of its piston-rod, the point where it stands, when quite "exhausted, is marked from an observation of a barometer "communicating with the same exhausted vessel, and the "scale divided accordingly."

"The joints of the cylinder, and other parts of Newco"men's engines, were generally made tight by being screwed

together upon rings of lead covered with glazier's putty, "which method was sufficient, as the entry of small quan"tities of air did not materially affect the working of those engines where only a very imperfect exhaustion was required. But the contrary being the case in the improved "engines, this method would not answer Mr. Watt's purpose. "He at first made his joints very true, and screwed them together upon pasteboard, softened by soaking in water, "which answered tolerably well for a time, but was not sufficiently durable. He therefore endeavoured to find out "some more lasting substance; and, observing that at the "iron foundries they filled up flaws by iron borings or filings "moistened by an ammoniacal liquor, which in time became

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The Life of James Watt: With Selections from His Correspondence