In 1814, an engine was constructed at Killingworth colliery, near Newcastle, having two cylinders with a cylindrical boiler, and working two pair of wheels by cranks placed at right angles, so that when one was in full operation, the other was at its dead points. By these means the propelling power was always in ac tion. The cranks were maintained in this position by an endless chain, which passed round the two cog wheels placed under the engine, and fixed on the same axles on which the wheels were placed. The wheels in this case were fixed on the axles, and turned with them.
In an engine subsequently constructed by Mr. Stevenson for the same railway, the mode adopted of connecting the wheels by an endless chain and cog wheels was abandoned, and the same effect was produced by connecting the two cranks by a straight rod. This method is still used in the coupled en gines which are applied to draw the trains of merchandise on the present railways.
The next stimulus which the progress of . this invention received, arose from the project of constructing a railway be tween Liverpool and Manchester, for the purpose of general traffic. When this project was undertaken it was not decided what moving power was most eligible whetherhorse power, stationary steam en gines, or locomotive engines : but the first for many obvious reasons, was soon reject ed, in favor of one or other of the last two.
The steam engine may be applied to move carriages on a railway by two dis tinct methods. By one, the engine is fixed and draws a train of carriages towards it by a rope extending the whole length of the road on which the engine works. By this method the line is divi ded into a number of short stages, at the extremity of each of which an engine is placed. The wagons or carriages, when drawn by an engine to its station, are de tached, and connected with the extremity of the rope-work by the next stationary engine, and thus the journey is performed from station to station by separate en gines. By the other method, each load transported along the lines drawn by an engine which travels with it as horses travel with a carriage on a common road.
Until the period to which we now ad vert, railways had been almost exclusive ly confined to the transport of mineral products from the mines up to the places of shipment, and to this purpose exclu sively had the locomotive engine been applied ; but the ends to be attained by a railway of thirty miles in length, con necting the largest manufacturing town, in the greatest manufacturing country in the world, with the greatest, most active, and most opulent commercial port, were of a nature so much more extensive and important, that it was considered that more than ordinary means should be re sorted to to obtain a moving power com mensurate with the traffic which might be expected under such circumstances.
Prizes were therefore proposed to be given, under certain stipulations, to those who would construct the most effective locomotive engines for the purposes of the road. This proposal produced, as was anticipated, much competition ; and the spirit of emulation being roused, a trial was appointed, which took place on the railway in October, 1829. Engines of several forms were produced ; and the prize was awarded to one, called the Rocket, constructed by Mr. Robert Ste venson, the son of Mr. George Stevenson, the engineer of the railway. In the first trial, this engine attained the then aston ishing speed of twenty-nine miles an hour ; and when, unhappily, at the cere mony of the opening of the railway, the accident occurred which deprived the country of Mr. Huskisson, his wounded body was conveyed by the same engine, a distance of about fifteen miles in twen ty-five minutes, being at the rate of thirty six miles an hour.
The circumstances in this mechanical arrangement, on which the rapid pro-. duction of steam depends, are two-fold : first, the extensive surface exposed to the radiant beat of the fire, by the casing surrounding the fire box, and by the tubes, twenty-five in number and only three inches in diameter, by which the flame and, heated air are conducted through the boiler from the fire box to the chimney ; and, secondly, by the power ful draught maintained in the furnace by the current of steam constantly discharged up the chimney. It has been mainly by bringing these principles more fully into operation, that all the improvements since made in the locomotive engine have been effected.
The railway was not long in operation, when the arrangement of the tubes in the boiler was improved ; their number was increased from twenty-five to one hundred and upwards, and their diame ters diminished from three inches to an inch and a half. This change alone pro duced an increased efficiency of the fuel, the proportion of nearly two to one ; the consumption of coke in the Rocket hav ing been very nearly 21 pounds per ton per mile, while, by the change above mentioned, the consumption of fuel in the new engines was reduced to lt pound per ton per mile. The position of the cylinder was also advantageously changed. Instead of being placed, as in the Rocket, outside the boiler, and exposed to the cold, air, through which the engine passed with such a velocity, they were now placed in that part of the engine called the smoke box, an enclosed space at the base of the chimney, into which the flame and heated air escaping from the tubes passed. By this arrangement the cylin ders were always maintained as hot as the air which issued from the fines, and all condensation of steam by their ex posure prevented.