engine. He then thought that, by conveying the eduction steam into the chimney by means of a small pipe after it had performed its office in the cylinders, and allowing it to escape in a vertical direction, its velocity would be imparted to the smoke from the fire, or to the ascending current of air in the chimney, thereby increasing the draft, and consequently the intensity of combustion in the furnace.

The experiment was no sooner made than the power of the engine was at once more than doubled: combustion was stimulated by the blast; consequently the capability of the boiler to generate steam was greatly increased, and the effective power of the engine augmented in precisely the same proportion, without in any way adding to its weight.

This simple but beautiful expedient, though it has hitherto received but slight notice as an original idea on the part of its author, was really fraught with the most important consequences to railway communication; and it is not too much to say that the success of the locomotive depended upon its adoption. Without the steam blast, the advantages of the "multitubular boiler" could never have been fairly tested;

* Mr. Nicholas Wood gives the following account of the circumstances which led to the invention of the steam blast by Mr. Stephenson:-"When the engines were first made, the steam escaped into the atmosphere, and made comparatively little noise. It was found difficult thus to produce steam in sufficient quantity to keep the engine constantly working, or rather to obtain an adequate rapidity of current in the chimney to give sufficient intensity to the fire. To effect a greater rapidity, or to increase the draft of the chimney, Mr. Stephenson thought that, by causing the steam to escape into the chimney through a pipe with its end turned upwards, the velocity of the current would be accelerated; and such was the effect." (Practical Treatise on Railroads, by Nicholas Wood, C.E. Ed. 1825, p. 292.) This passage clearly shows the preconceived design and purpose of Mr. Stephenson in inventing the steam blast. A claim has, nevertheless, been set up in behalf of Timothy Hackworth as its inventor in 1829, although the design, mechanism, and rationale of the invention, as effected by Mr. Stephenson in 1815, and adopted by him in all the Killingworth engines from that year downwards, were clearly described by Mr. Wood in 1825!

CHAP. IX.]

INVENTION OF THE STEAM BLAST.

93

and it was these two improvements, working together, which afterwards secured the triumph of the locomotive on the opening of the Liverpool and Manchester Railway. Without the steam blast, by which the intensity of combustion was kept up to the highest point, and the evolution of steam thus rapidly effected, high rates of speed by means of the combustion of coke could not have been attained, and locomotives might still have been dragging themselves unwieldily along at little more than five or six miles an hour.

The steam blast had scarcely been adopted, with so decided a success, when Mr. Stephenson, observing the numerous defects in his engine, and profiting by the experience which he had already acquired, determined to construct a second engine, in which to embody his improvements in their best form. Careful and cautious observation of the working of his locomotive had convinced him that the complication arising out of the action of the two cylinders being combined by spurwheels would prevent its coming into practical use. He accordingly directed his attention to an entire change in the construction and mechanical arrangements of the machine; and in the following year, conjointly with Mr. Dodds, who provided the necessary funds, he took out a patent, dated the 28th of February, 1815*, for an engine which combined in a remarkable degree the essential requisites of an economical locomotive; that is to say, few parts, simplicity in their action, and directness in the mode by which the power was communicated to the wheels supporting the engine.

This locomotive, like the first, had two vertical cylinders, which communicated directly with each pair of the four wheels that supported the engine, by means of a cross head and a

* A grant to Ralph Dodds and George Stephenson, both of Killingworth, engineers, for their various Improvements in the Construction of Locomotive Engines. Patent Office, No. 3887.

yur of connecting-rods. But, in attempting to establish a rect communication between the cylinders and the wheels I rolled upon the rails, considerable difficulties presented hanselves The ordinary joints could not be employed to ... the parts of the engine, which was a rigid mass, with the his ning upon the irregular surface of the rails; for il that the two rails of the line of wayAny in the early days of imperfect construction AAN - could not always be maintained at —that the wheel at one end of the axle might of the line which had subsided, ver hei wod be comparatively elevated; 2 MAY 28 axle and wheels, it was obvious cara berween the cross head and the 11e Hee it became necessary to

cona yun ah ah rod where it united with he cross head to preserve ties via de sale of the wheels with which

ver the bee of exibility combined with but was er for ensuring power and seling nowless and jas from irregularities in the 4. Nehense made of the ball and socket" Ponas estance to the hip-joint of the deoding in between the ends of the edhe per ex and with the connecting rods, and who the onecting rods where they were

www she is attached to each driving wheel. By this arrangement the parallelism between the cross head and the axle was at all times maintained and preserved, without producing any serious jar or friction on any part of the machine

important point was, to combine each pair of means of some simple mechanism, instead of by

CHAP. IX.]

HIS SECOND LOCOMOTIVE.

95

the cogwheels which had formerly been used. And, with this object, Mr. Stephenson began by making in each axle cranks at right angles to each other, with rods communicating horizontally between them.

A locomotive was accordingly constructed upon this plan in the year 1815, and it was found to answer extremely well. But at that period the mechanical skill of the country was not equal to the task of forging cranked axles of the soundness and strength necessary to stand the jars incident to locomotive work. Mr. Stephenson was accordingly compelled to fall back upon a substitute, which, although less simple and efficient, was within the mechanical capabilities of the workmen of that day, in respect of construction as well as repair. He adopted a chain which rolled over indented wheels placed on the centre of each axle, and so arranged that the two pairs of wheels were effectually coupled and made to keep pace with each other. The chain, however, after a few years' use, became stretched; and then the engines were liable to irregularity in their working, especially in changing from working back to working forward again. Eventually the chain was laid aside, and the front and hind wheels were united by rods on the outside, instead of by rods and crank axles inside, as specified in the original patent. This expedient completely answered the purpose required, without involving any expensive or difficult workmanship.

Thus, in the year 1815, Mr. Stephenson, by dint of patient and persevering labour,-by careful observation of the works of others, and never neglecting to avail himself of their suggestions, had succeeded in manufacturing an engine which included the following important improvements on all previous attempts in the same direction:-viz., simple and direct communication between the cylinder and the wheels rolling upon the rails; joint adhesion of all the wheels, attained by the use of horizontal connecting rods; and finally, a beautiful method

of exciting the combustion of the fuel by employing the waste steam, which had formerly been allowed uselessly to escape into the air. Although many improvements in detail were afterwards introduced in the locomotive by Mr. Stephenson himself, as well as by his equally distinguished son, it is perhaps not too much to say that this engine, as a mechanical contrivance, contained the germ of all that has since been effected. It may in fact be regarded as the type of the present locomotive engine.