STEAM ENGINE, 



385 



low that of boiling water." " When steam issues 

 from.the spout of a boiling tea-kettle, it is at first 

 invisible, and it is not till it has advanced some 

 distance in the air, that it begins to assume the ap- 

 pearance of a visible cloud. But condensed steam 

 is visible the moment that it issues from the pipe. 

 The high pressure steam, supposing the elasticity 

 double, occupies only half the space of low pressure 

 steam. The moment it comes into the atmosphere 

 its volume is doubled. This occasions a prodigious 

 increase in the capacity for heat, and at the same 

 time mixes it with the cold atmospheric air. These 

 two circumstances sink its temperature so low that 

 it is no longer capable of scalding." 



When steam is brought into contact with cold 

 bodies, so that parting with a portion of its heat it 

 is reduced below the temperature of 212, it again 

 assumes the liquid form and occupies 1700 times 

 less space. This is called condensation. Upon this 

 property, and upon its expansibility, depends its 

 efficacy as a propeller of machinery, as will be 

 shown in the subsequent article. 



STEAM ENGINE, a mechanical contrivance, 

 whereby stearn is made to produce continuous mo- 

 tion. 



History. The first idea of employing steam as a 

 motive power, seems to have occurred to Hiero of 

 Alexandria, who flourished about 40 B. C. He in- 

 troduced high pressure steam into the interior of a 

 hollow globe, revolving upon an axis, and having 

 two projecting tubes from the sides, through which 

 the steam escaped into the atmosphere, and by the 

 reaction arising from its escape into the air, the globe 

 was made to revolve. This engine acted on the 

 same principle as Barker's mill. In 1629, Branca, 

 an Italian, published an account of another form of 

 steam engine, in which the steam, issuing out from 

 a tube in the boiler, impinged upon the floats of a 

 wheel, and turned it round. These contrivances 

 are so trifling in their nature, so far as utility is 

 concerned, that they need scarcely be mentioned. 

 The first approaches at any thing like a useful ma- 

 chine was made by the marquis of Worcester, who, 

 in a work entitled a Century of the Names and 

 Scantlings of Inventions, published in the year 1668, 

 gave an account of it, from which we may infer 

 that his engine acted somewhat after the following 

 manner. Suppose a long upright tube, furnished at 

 the top with a valve opening upwards, and com- 

 municating with a vessel containing water. When 

 steam is thrown upon the surface of the water, it 

 will force the water up the pipe to a height greater 

 in proportion as the force of the steam exceeds the 

 elasticity of the air. The valve at the top of the 

 pipe would prevent the water from returning when 

 the steam was cut off. The inventor designates 

 his contrivance, " an admirable and most forcible 

 way to drive up water by means of fire ;" yet the 

 description of this engine, which forms the sixty- 

 eighth of his century of inventions, is, like most of 

 the others, in no way remarkable for its perspicui- 

 ty ; but his contrivance was inefficient in practice. 

 He was the inventor of the digester that goes by 

 his name, and of course the first who proposed or 

 used a safety valve. Amontons and Deflander in 

 1692, proposed steam wheels, neither of which could 

 be brought into useful action. Six years subsequent 

 to the above date, Thomas Savary took out letters 

 patent for a steam engine. During the course of 

 the following year, he exhibited a working model 

 of it before the Royal Society of London. The 

 proposed use of Savary 's engine was the draining of 



mines, and consisted of a long pipe inserted into 

 the well to be drained, in which pipe a valve was 

 placed, opening upwards, and at a height in the 

 pipe not exceeding twenty feet above the surface 

 of the water to be raised. Immediately above 

 this valve a side pipe branched off from the main 

 pipe, and formed a communication between it, and 

 a hollow vessel, called the receiver. In the main 

 pipe, and immediately above that part where 

 the receiver pipe branched off, there was another 

 valve opening upwards, and the top of the main 

 pipe opened into the cistern, where the water was 

 to be delivered. The receiver communicated with 

 the boiler by means of a pipe furnished with a stop 

 cock, which might be opened or shut at pleasure, 

 and the receiver was connected in a similar way 

 with the cold water cistern. Steam was admitted 

 into the receiver and consequently into the main pipe, 

 above the lower valve. When this was the case, 

 the steam cock was shut, and cold water let into 

 the receiver by the other pipe ; the steam was con- 

 densed and a vacuum formed in the receiver and 

 main pipe, and the water, by the action of the at- 

 mosphere, pressed up the main pipe from the well, 

 and was prevented from returning by the lower valve 

 which was closed by the weight of the fluid above 

 it. In this state of things the steam was again ad- 

 mitted into the receiver, and acting upon the water 

 in the main pipe, forced it through the upper valve 

 up the pipe and into the cistern. The steam, of 

 course, would at the same time force down the un- 

 der valve, and prevent the water from returning to 

 the well. Several ingenious mechanics have en- 

 deavoured to improve the engine of Savary, among 

 whom may be more especially mentioned Mr Ponti- 

 fax, Mr J. Boaz, and Mr G. Whitelaw. There 

 were several engines erected on Savary's principle, 

 but the introduction of Newcomen's, in 1705, caused 

 it to be abandoned. Letters patent were granted 

 in that year to Thomas Newcomen, a blacksmith, 

 and John Cawley, a plumber, both of Dartmouth, in 

 j conjunction with captain Savary, for a new engine 

 i for raising water from mines. This captain Savary, 

 it is to be observed, is the same Thomas Savar y, 

 ; above spoken of ; he was neither a captain in the 

 i army or navy, but received the title from the min ers, 

 j who are in the habit of calling their overseers cap- 

 , tains. The nature of this invention may be de- 

 scribed as follows. A solid piston was fitted in to a 

 hollow cylinder, and so contrived that it was cap- 

 able of moving up and down without difficulty, yet 

 at the same time so accurately fitted that, while 

 even in a state of motion, no air or steam was al- 

 lowed to escape between it and the cylinder. In to 

 this piston a rod was fixed, attached to one end of 

 a long beam, suspended in the middle, and having 

 i the pump rods at the other end. The weight of 

 the pump rods was such as to draw down that end 

 of the beam, and by raising the other, lift the piston 

 ! to the top of the cylinder. In this position steam 

 was introduced into the bottom of the cylinder, so 

 as to fill the whole space below the piston, and 

 when this was done cold water was introduced, 

 which converted the steam into water, or condensed 

 it, and formed a vacuum in the cylinder below the 

 piston. The pressure of the air on the upper sur- 

 face of the piston forced it down to the bottom of 

 the cylinder, raised the pump rods at the other end 

 of the beam, and thus drew the water from the well. 

 The re-admission of steam below the piston would 

 destroy the vacuum, and the piston would be drawn 

 to the top of the cylinder by the weight of the 

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