CHAMBERS'S INFORMATION FOR THE PEOPLE. 



cylinder, and consequently raises the other end of 

 the beam, to which the pump-rod, N, is attached. 

 In this manner, the water is raised from the mine, 

 and by a repetition of the movements already 

 noticed, a constant discharge of water results. 



It will be noticed that the work in this engine is 

 not clone by the pressure of the steam, but by the 

 pressure of the atmosphere on the upper side of 

 the piston, when the steam in the cylinder is 

 reduced by condensation to a very small density. 

 Hence arises its name of ' atmospheric ' engine. 



At the beginning of the i8th century, a boy 

 named Humphrey Potter (to save, it is said, the 

 trouble of personal superintendence) devised a 

 system of strings and levers, by which the engine 

 was made to work its own valves. In 1717, Henry 

 Beighton, an F.R.S., invented a simpler and more 

 scientific system of ' hand-gear,' which rendered 

 the engine completely self-acting. During the 

 latter part of the time that elapsed before Watt's 

 discoveries changed everything, Smeaton brought 

 Newcomen's engine to a very high degree of per- 

 fection. As the result of study and experiment, 

 he made many improvements in it, in the form of 

 the boiler, the proportions of the cylinder, &c. It 

 was he, too, who invented the cataract, a very 

 ingenious self-acting valve arrangement, which is 

 still universally used in Cornish engines. It is 

 worth mentioning that, in 1725, Leupold invented 

 an engine in which steam of a higher pressure 

 than that of the atmosphere was employed in the 

 cylinder, but his engine possessed defects that 

 prevented it ever being practically used. 



Great as was the advance of the steam-engine 

 between 1700 and 1770, its defects were still most 

 serious, the chief among them being its enormous 

 waste of heat. Much steam was lost in reheating 

 the cylinder after each condensation, for it had 

 always at least to be raised to the temperature of 

 the steam before the steam could, as such, con- 

 tinue in it, and be in any degree efficient ; and on 

 the other hand, the cold air which followed the 

 descent of the piston necessarily withdrew a con- 

 siderable portion of heat. By the calculations of 

 Watt, it was estimated that three times as much 

 steam was expended in this manner as would have 

 been equal to work the engine a loss, therefore, 

 equal to 75 per cent. Nevertheless, this, as has 

 been correctly observed, ' was the first really 

 efficient steam-engine that is, the first engine 

 which could be applied profitably and safely to 

 the most important purposes for which such 

 machines were required at the time of its 

 invention.' 



The great philosopher and inventor, James 

 Watt, to whom we really owe the steam-engine 

 in its present form, was, as is well known, a 

 mathematical instrument-maker in Glasgow. He 

 appears to have made experiments on the proper- 

 ties of steam about 1761, but it was not till three 

 years afterwards that he took the steam-engine up 

 in earnest. In 1764, he had to repair, in the 

 course of his business, a model of an atmospheric 

 engine belonging to the university of Glasgow. It 

 was a very small machine, with a cylinder 2 inches 

 diameter, and 6 inches stroke. Its defects, how- 

 ever, led him to study its principles (a thing 

 which no one had really done before him), and 

 in the course of a few years he had given to the 

 world the wonderful series of inventions which 

 practically made the steam-engine what it is 



424 



still, all subsequent improvements having been 

 comparatively matters of detail. 



Former inventors and improvers had worked at 

 the steam-engine empirically ; Watt went into the 

 whole matter scientifically. He studied the pro- 

 perties of heat, and the laws of elastic fluids, as 

 far as they were known in his time, and the rela- 

 tions between the temperature, volume, and pres- 

 sure of steam. In the specification of his patent 

 of 1769 he embodied the principles which his 

 studies had led him to recognise in the following 

 memorable clauses : 



'My method of lessening the consumption of 

 steam, and consequently fuel, in fire-engines, 

 consists of the following principles : 



' First, That vessel in which the powers of steam 

 are to be employed to work the engine, which is 

 called the cylinder in common fire-engines, and 

 which I call the steam-vessel, must, during the 

 whole time the engine is at work, be kept as hot 

 as the steam which 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 condensation of steam, the 

 steam is to be condensed in vessels distinct from 

 the steam-vessels or cylinders, although occasion- 

 ally communicating with them \ these vessels I 

 call condensers ; and whilst the engines are work- 

 ing, these condensers ought at least to be kept as 

 cold as the air in the neighbourhood of the engines, 

 by application of water, or other cold bodies. 



' 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 of the steam-vessels or condensers 

 by means of pumps, wrought by the engines them- 

 selves, or otherwise. 



' Fourthly, I intend, in many cases, to employ 

 the expansive force of steam to press on the 

 pistons, or whatever may be used instead of them, 

 in the same manner in which the pressure of the 

 atmosphere is now employed in common fire- 

 engines. 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. 



' Lastly, Instead of using water to render the 

 pistons and other parts of the engines air and 

 steam tight, I employ oils, wax, resinous bodies, 

 fat of animals, quicksilver, and other metals in 

 their fluid state.' 



Watt's principal inventions were isf, The con- 

 densation of steam in a vessel separate from the 

 cylinder, so as to avoid the cooling of the latter ; 

 2d, The use of a pump, called an ' air-pump,' to 

 withdraw the condensed water, and mixed steam 

 and air, from the condenser; 3^, To surround 

 I the cylinder either with a steam-jacket, or with 

 , some non-conducting body, in order to prevent 

 \ radiation of heat (these three, with others, were 

 included in the specification of 1769) ; 4/4, To 

 : use the steam expansively in the way explained 

 in a former part of this article (this was invented 

 before 1769, but not published till 1782); and 

 5//z, The now universally used double-acting 

 engine, and the conversion of the reciprocating 



