510 



LOCOMOTIVE ENGINE. 



qualities of substnnce and structure, no piece of inert 

 meclianism is so favourably adapted as the wheel- 

 carriage. It was introduced into use in very early 

 ages. Wheels diminish friction, and also surmount 

 obstacles or inequalities of the road, with morn 

 advantage tlian bodies of any other form, in their 

 place, could do. The friction is diminished by 

 transferring it from the surface of the ground to 

 the centre of the wheel, or, rather, to the place 

 of contact between the axletree and the box of the 

 wheel ; so that it is lessened by the mechanical 

 advantage of the lever, in the proportion which the 

 diameter of the axletree bears to the diameter of the 

 wheel. The rubbing surfaces, also, being kept 

 polished, and smeared with some unctuous sub- 

 stance, are in the best possible condition to resist 

 friction. In like manner, the common obstacles 

 that present themselves in the public roads, are 

 surmounted by a wheel wilh peculiar facility. As 

 soon as the wheel strikes against a stone or similar 

 hard body, it is converted into a lever for lifting the 

 load over the resisting object. If an obstacle eight 

 or ten inches in height were presented to the body 

 of a carriage unprovided with wheels, it would stop 

 its progress, or subject it to such violence as would 

 endanger its safety. But by the action of a wheel, 

 the load is lifted, and its centre of gravity passes 

 over in the direction of an easy arc, the obstacle 

 furnishing the fulcrum on which the lever acts. 

 Rollers placed under a heavy body diminish the 

 friction in a greater degree than wheels, provided 

 they are true spheres or cylinders, without any axis 

 on which they are constrained to move ; but a cylin- 

 drical roller occasions friction, whenever its path 

 deviates in the least from a straight line. The 

 mechanical advantages of a wheel are proportionate 

 to its size, and the larger it is, the more effectually 

 does it diminish the ordinary resistances. A large 

 wheel will surmount stones and similar obstacles 

 better than a small one, since the arm of the lever 

 on which the force acts is longer, and the curve 

 described by the centre of the load is the arc of a 

 larger circle, and, of course, the ascent is more 

 gradual and easy. In passing over holes, ruts, or 

 excavations, also, a large wheel sinks less than a 

 small one, and consequently occasions less jolting 

 and expenditure of power. The wear also of large 

 wheels is less than that of small ones, for if we 

 suppose a wheel to be three feet in diameter, it 

 will turn round twice, while one of six feet in dia- 

 meter turns round once ; so that its tire will come 

 twice as often in contact with the ground, and its 

 spokes will twice as often have to support the weight 

 of the load. In practice, however, it is found neces- 

 sary to confine the size of wheels within certain 

 limits, partly because the materials used would make 

 wheels of great size heavy and cumbersome, since the 

 separate parts would necessarily be of large pro- 

 portions to have the requisite strength, and partly 

 because they would be disproportioned to the size of 

 the animals employed in draught, and compel them 

 to pull obliquely downwards, and therefore to expend 

 a part of their force in acting against the ground. 



LOCOMOTIVE ENGINE is that which is cal- 

 culated to produce locomotion, or motion from place 

 to place. 



In this article, it is our intention to give an his- 

 torical and descriptive account of locomotive engines, 

 and to reserve the consideration of their effects upon 



ailways, until we come to treat of railways, (q. v.) 

 I)r Robinson, while a student at Glasgow college in 



1759, seems to have been the first who suggested the 

 application of steam power to the propelling of 

 carriages. Oliver Evans, an ingenious American, 

 thought of the same thing twenty-three years after 



wards, but it does not appear that any thing more 

 than a good high pressure fixed engine was the result 

 of his labours. In 1784, James Watt took out a 

 patent for the application of his steam engine to 

 move carriages, and three years afterwards, Mr 

 William Symington exhibited a model of a steam 

 carriage of his own invention at Edinburgh, the 

 engine being of the low pressure kind. In 1802, a 

 carriage on four wheels, was erected by Mr Richard 

 Trevithick, having a high pressure engine and boiler 

 contained in the carriage. The great defect of 

 Trevithick's carriage, consisted in the slipping of 

 the wheels, which Mr Blinkensop endeavoured to 

 obviate in 1811, by employing a rack rail, in which a 

 large toothed wheel was to work. In the year fol- 

 lowing, Messrs Chapman brought forward a steam 

 carriage, in which the weight was distributed over a 

 larger surface, and consequently less injury done to the 

 rail. About the same time, Mr Brunton of Batterly, 

 contrived a carriage to be propelled by fevers, act- 

 ing like horse's feet. A railway carriage invented 

 by M George Stevenson in July, 1814, was reckoned 

 the most perfect for many years. That gentleman 

 employed two cylinders, and increased the efficacy 

 of the machine, by distributing the friction over 

 four wheels, instead of over two as in Trevithick's 

 machine. In 1830, steam carriages of a still bet- 

 ter construction, were started upon the Liverpool 

 and Manchester railway. The carriages tried were 

 the Sanspareil by Mr Hawkworth, the Novelty 

 by Messrs Braithwait and Ericson, and the Rocket 

 by Mr Stevenson : after a fair trial, the Rocket 

 obtained the reward. Mr Stevenson has, how- 

 ever, made farther improvements upon his steam 

 carriage, which we shall now proceed to describe. 

 Various views of this railway steam carriage are 

 given in plates 51. No. l,and 51. No. 2. A side 

 elevation is shown in fig. 1, plate 51. No. 1; figs. 2 

 and 3 are end elevations, the former showing the 

 back, and the latter the front elevation, fig. 4, is an 

 end view of the boiler. Fig. 1, plate 51. No. 2. is a 

 ground plan, and fig. 2 a section and 3 a side view, with 

 some parts taken away, in order to show the more 

 concealed portions of the machinery. The same let- 

 ters of reference are used in all the figures. 



Our attention must in the first place, be directed 

 to the boiler, an end view of which is represented in 

 fig. 4, plate 51. No. 1. It consists of a metallic 

 cylinder, having two flat ends, the cylinder being 

 commonly about six feet in length. The under half 

 of this cylinder is occupied by eighty or 100 copper 

 tubes traversing the whole length, and each of about 

 lg inches diameter. These tubes are so many flues 

 being open at both ends, the one end communicating 

 with the fire box, or furnace, and the other opening 

 into the chimney, thus affording a passage for the 

 smoke and hot air. These pipes being heated, they 

 communicate their caloric to the water which sur- 

 rounds them, the boiler or cylinder being filled with 

 water to such a height as to cover the tubes. The 

 boiler lies lengthwise in the carriage, as may be seen 

 at A A' in the longitudinal section, fig. 2, plate 51. 

 No. 2. One end of the boiler, as was before observed, 

 opens into a fire-box or furnace, seen at b b a I in the 

 same section. The furnace bars are laid horizontally 

 at a, as may be seen also in the ground plan, fig. 

 1, plate 51. No. 2. The fire box or furnace, is a 

 square box formed of two casings, the one with- 

 in the other, with a space between them to contain 

 I water, and communicating with the boiler, and in 

 fact forms part of it. Therefore when water is pour- 

 ed into the boiler it flows into the space between the 

 casings round the fire-box, and as the boiler is con- 

 stantly kept about half filled with water, the space 

 is always full. 



