James 1736-1819 Watt

A still later invention was the centrifugal governor, by which the speed of rotative engines was automatically controlled. An other of Watt's contributions to the development of the steam engine is the indicator, which draws a diagram of the relation of the steam's pressure to its volume as the stroke proceeds. The eminently philosophic notion of an indicator diagram is funda mental in the theory of thermodynamics; the instrument itself is to the steam engineer what the stethoscope is to the physician.

The commercial success of the engine was not slow. By 1783 all but one of the Newcomen pumping-engines in Cornwall had been displaced by Watt's. The mines were then far from thriving; many were even on the point of being abandoned through the difficulty of dealing with large volumes of water; and Watt's invention, by its economy, gave many of them a new lease of life. His engine used no more than a fourth of the fuel that had for merly been needed to do the same work, and the Soho firm usually claimed as royalty a sum equivalent to one-third of the saving.

Before Watt's time the steam-engine was exclusively a steam

pump, slow-working, cumbrous and excessively wasteful in fuel. His first patent made it quick in working, powerful and efficient, but still only as a steam-pump. His later inventions adapted it to drive machinery of all kinds, and left it virtually what it is to-day, save in three respects. In respect of mechanical arrange ment the modern engine differs from Watt's chiefly in that the beam, an indispensable feature in the early pumping-engines, has gradually given way to more direct modes of connecting the pis ton with the crank. The second difference is in the modern use of high-pressure steam. It is remarkable that Watt, notwithstand ing the fact that his own invention of expansive working must have opened his eyes to the advantage of high-pressure steam, declined to make use of it. He persisted in the use of pressures that were little if at all above that of the atmosphere, while Trevithick ven tured as far as 120 lb. on the square inch, a curious episode in the history of the steam-engine is an attempt by Boulton and Watt to obtain an act of parliament forbidding the use of high pressure steam on the ground that the lives of the public were endangered. The third respect in which a great improvement has been effected is in the introduction of compound expansion. Here, too, we find the Soho firm hostile, though the necessity of defending their monopoly makes their action natural enough. Hornblower had in fact stumbled on the invention of the compound engine, but as his machine employed Watt's condenser it was suppressed, to be revived after some years by Arthur Woolf (1766-1837). Watt in one of his patents (1784) describes a steam locomotive, but he never prosecuted this, and when William Murdoch, his chief assistant (famous as the inventor of gas-lighting), made experi ments on the same lines, Watt gave, him little encouragement. The notion then was to use a steam carriage on ordinary roads; its use on railways had not yet been thought of. When that idea

took form later in the last years of Watt's life, the old man refused to countenance it.

On the expiry in 1800 of the act by which the patent of 1769 had been extended, Watt gave up his share in the business of engine-building to his sons, James, who carried it on with a son of Boulton for many years, and Gregory, who died in 1804. The remainder of his life was quietly spent at Heathfield Hall, near Birmingham, where he devoted his time to mechanical pur suits. His last work was the invention of machines for copying sculpture, one for making reduced copies, another for taking facsimiles by means of a light frame, which carried a pointer over the surface of the work, while a revolving tool fixed to the frame alongside the pointer cut a corresponding surface on a suitable block. We find him not many months before his death, presenting copies of busts to his friends as the work "of a young artist just entering on his eighty-third year." His life drew to a tranquil close, and the end came at Heathfield on Aug. 19, 1819. He was buried in the parish church of Handsworth.

Watt was twice married—first in 1763 to his cousin Margaret Miller, who died ten years later. Of four children born of the marriage, two died in infancy; another was James (1769-1848), who succeeded his father in business ; the fourth was a daughter. His second wife, Anne Macgregor, whom he married before settling in Birmingham in 1775, survived him; but her two chil dren, Gregory and a daughter, died young.

One of Watt's minor inventions was the press, patented in 1780, for copying manuscript by using a glutinous ink and pressing the written page against a moistened sheet of thin paper.

In the domain of pure science Watt claims recognition as a discoverer of the composition of water. Writing to Joseph Priestley in April 1783, with reference to some of Priestley's ex periments, he suggests the theory that "water is composed of de phlogisticated air and phlogiston deprived of part of their latent or elementary heat." Watt's views were communicated to the Royal Society in 1783, Cavendish's experiments in 1784, and both are printed in the same volume of the Philosophical Transactions.

He was a man of warm friendships, and has numerous letters. They are full of insight : his own achievements are told with modesty and dry humour. In his old age Watt is described as a man stored with knowledge, full of anecdote, familiar with modern languages and a great talker. Scott so writes of him.

See J. P. Muirhead, Origin and Progress of the Mechanical Inven tions of James Watt (3 vols., 1854) ; Muirhead, Life of Watt (1858) ; Smiles, Lives of Boulton and Watt; Williamson, Memorials of the Lineage, etc., of James Watt, published by the Watt Club (Greenock, 1856) ; Correspondence of the late James WatL, on his Discovery of the Theory of the Composition of Water, edited by Muirhead (1846) ; Cowper "On the Inventions of James Watt and his Models preserved at Handsworth and South Kensington," Proc. Inst. Mech. Eng. (1883) ; Robison, Mechanical Philosophy, vol. ii. (1822).