James Watt (19 January 1736 – 25 August 1819) was a Scottish inventor and mechanical engineer whose improvements to the Newcomen steam engine were fundamental to the changes brought by the Industrial Revolution in both the Kingdom of Great Britain and the world.
- I can think of nothing else than this machine.
- in a letter to a friend, Dr. Lind, April 29, 1765.
"Notes on Professor Robison's Dissertation on Steam-engines" (1769)
"Notes on Professor Robison's Dissertation on Steam-engines" (1769) from Robison's Essays on Various Subjects of Mechanical Philosophy (1822) ed. David Brewster Vol. 2, p. 347
- About the year 1761, or 1762, I tried some experiments on the force of steam in a Papin's digester, and formed a species of steam-engine by fixing upon it a syringe, one-third of an inch diameter, with a solid piston, and furnished also with a cock to admit the steam from the digester, or shut it off at pleasure, as well as to open a communication from the inside of the syringe to the open air, by which the steam contained in the syringe might escape. When the communication between the digester and syringe was opened, the steam entered the syringe, and by its action upon the piston raised a considerable weight (15 lbs.) with which it was loaded. When this was raised as high as was thought proper, the communication with the digester was shut, and that with the atmosphere opened; the steam then made its escape, and the weight descended. The operations were repeated, and, though in this experiment the cock was turned by hand, it was easy to see how it could be done by the machine itself, and to make it work with perfect regularity. But I soon relinquished the idea of constructing an engine upon its principle, from being sensible it would be liable to some of the objections against Savery's engine, viz., the danger of bursting the boiler, and the difficulty of making the joints tight, and also that a great part of the power of the steam would be lost, because no vacuum was formed to assist the descent of the piston. I, however, described this engine in the fourth article of the specification of my patent of 1769; and again in the specification of another patent in the year 1784, together with a mode of applying it to the moving of wheel-carriages.
- In the winter of 1763-4, having occasion to repair a model of Newcomen's engine belonging to the Natural Philosophy class of the University of Glasgow, my mind was again directed to it. At that period my knowledge was derived principally from Desaguliers, and partly from Belidor. I set about repairing it as a mere mechanician; and when that was done, and it was set to work, I was surprised to find that its boiler could not supply it with steam, though apparently quite large enough... By blowing the fire it was made to take a few strokes, but required an enormous quantity of injection water, though it was very lightly loaded by the column of water in the pump. It soon occurred that this was caused by the little cylinder exposing a greater surface to condense the steam, than the cylinders of larger engines did in proportion to their respective contents. It was found that by shortening the column of water in the pump, the boiler could supply the cylinder with steam, and that the engine would work regularly with a moderate quantity of injection. It now appeared that the cylinder of the model, being of brass, would conduct heat much better than the cast-iron cylinders of larger engines, (generally covered on the inside with a stony crust), and that considerable advantage could be gained by making the cylinders of some substance that would receive and give out heat slowly. Of these, wood seemed to be the most likely, provided it should prove sufficiently durable. A small engine was, therefore, constructed... made of wood, soaked in linseed oil, and baked to dryness. With this engine many experiments were made; but it was soon found that the wooden cylinder was not likely to prove durable, and that the steam condensed in filling it still exceeded the proportion of that required for large engines, according to the statements of Desaguliers. It was also found that all attempts to produce a better exhaustion by throwing in more injection, caused a disproportionate waste of steam. On reflection, the cause of this seemed to be the boiling of water in vacuo at low heats, a discovery lately made by Dr. Cullen and some other philosophers... and consequently at greater heats, the water in the cylinder would, produce a steam which would in part resist the pressure of the atmosphere.
- I perceived that, in order to make the best use of steam, it was necessary—first, that the cylinder should be maintained always as hot as the steam which entered it; and, secondly, that when the steam was condensed, the water of which it was composed, and the injection itself, should be cooled down to 100°, or lower, where that was possible. The means of accomplishing these points did not immediately present themselves; but early in 1765 it occurred to me, that if a communication were opened between a cylinder containing steam, and another vessel which was exhausted of air and other fluids, the steam, as an elastic fluid, would immediately rush into the empty vessel, and continue so to do until it had established an equilibrium; and if that vessel were kept very cool by an injection, or otherwise, more steam would continue to enter until the whole was condensed.
- In Newcomen's engine, the piston is kept tight by water, which could not be applicable in this new method; as, if any of it entered into a partially-exhausted and hot cylinder, it would boil, and prevent the production of a vacuum, and would also cool the cylinder by its evaporation during the descent of the piston. I proposed to remedy this defect by employing wax, tallow, or other grease, to lubricate and keep the piston tight. It next occurred to me, that the mouth of the cylinder being open, the air which entered to act on the piston would cool the cylinder, and condense some steam on again filling it. I therefore proposed to put an air-tight cover upon the cylinder, with a hole and stuffing-box for the piston-rod to slide through, and to admit steam above the piston to act upon it, instead of the atmosphere. ...There still remained another source of the destruction of steam, the cooling of the cylinder by the external air, which would produce an internal condensation whenever steam entered it, and which would be repeated every stroke; this I proposed to remedy by an external cylinder, containing steam, surrounded by another of wood, or of some other substance which would conduct heat slowly.
- When once the idea of the separate condensation was started, all these improvements followed as corollaries in quick succession, so that in the course of one or two days the invention was thus far complete in my mind, and I immediately set about an experiment to verify it practically.
Quotes about James Watt
- If the Steam Engine be the most powerful instrument in the hands of man, to alter the face of the physical world, it operates, at the same time, as a powerful moral lever in forwarding the great cause of civilization. ...If ...we are now met to consider of placing a monument to the memory of Mr. Watt beside the monuments of those who fell in the splendid victories of the last war, let it not be said that there is no connexion between the services of this modest and unobtrusive benefactor of his country, and the triumphs of the heroes which those monuments are destined to commemorate. ...It has been often said, that many of the great discoveries in science are due to accident; but it was well remarked by [Humphry Davy]... that this cannot be the case with the principal discovery of Mr. Watt. ... Again, it has frequently happened that those philosophers, who have made brilliant and useful discoveries... have only been able to turn their discoveries to the purpose of averting evils threatening, and often destroying, the precarious tenure of human existence. Thus Franklin disarmed the thunderbolt, and conducted it innocuous through our buildings, and close to our fire-sides—thus Jenner stripped a loathsome and destructive disease of its virulence, and rendered it harmless of devastation—thus [Davy]... sent the safety lamp into our mines to save... their useful inhabitants from the awful explosion of the fire damp. But the discovery of Mr. Watt went further: he subdued and regulated the most terrific power in the universe,—that power which, by the joint operation of pressure and heat, probably produces those tremendous convulsions of the earth, which in a moment subvert whole cities, and almost change the face of the inhabited globe. This apparently ungovernable power Mr. Watt reduced to a state of such perfect organization and discipline... that it may now be safely manœuvred and brought into irresistible action—irresistible, but still regulated, measured, and ascertained—or lulled into the most complete and secure repose, at the will of man, and under the guidance of his feeble hand. Thus one man directs it into the bowels of the earth, to tear asunder its very elements, and bring to light its hidden treasures; another places it upon the surface of the waters, to control the winds of heaven, to stem the tides, to check the currents, and defy the waves of the ocean; a third, perhaps and a fourth, are destined to apply this mighty power to other purposes, still unthought of and unsuspected, but leading to consequences, possibly not less important than those which it has already produced. ... those benefits, conferred by Mr. Watt on the whole civilized world, have been most experienced by his own country, which owes a tribute of national gratitude to a man, who has thus honoured her by his genius, and promoted her well being by his discoveries.
- William Huskisson, "Speech at the Public Meeting held at Freemasons' Hall, on the 18th June, 1824 for Erecting a Monument to the late James Watt; the Earl of Liverpool in the Chair," in The Speeches of the Right Honorable William Huskisson(1831)