confirmation to the decision of the directors, by exhibiting the great power of the locomotive, that it appears to have put the rival system out of sight for some years; but the idea of stationary power was too plausible not to be revived. The broad fact was obvious enough, that to convey an engine and its boiler through the air, at a speed of twenty or thirty miles an hour, exposed to all weathers, and to all accidents of a precarious road, and consuming a large portion of its energy in moving its own weight along, was not the most advantageous way of applying steam-power. It was not wonderful, therefore, that any plan should be received with favour, which offered an apparently feasible application, to railway haulage, of the power of an engine, safely housed with its various appurtenances in a fixed building, where it could be worked in the most advantageous way.

The invention of the atmospheric plan of propulsion offered this promise. It was assumed that the principal fault of the stationary system, as hitherto applied, lay in the rope, as a means of transferring the power from the fixed engine to the moving train; and undoubtedly, by its great friction and liability to accident, the rope was a serious evil. The principle of the atmospheric invention consisted simply in substituting for the rope another means of transmitting the power, which was conceived to be much superior, and the introduction of which, it was thought, would entirely remove the objections to the stationary system, and leave its admitted advantages available, without the drawbacks that had formerly interfered with its application.

The first idea of transmitting power to a distance by

means of pneumatic pressure appears to belong to the celebrated Denys Papin, who described, in 1688, an apparatus, in which a partial vacuum, produced in a long tube by air-pumps fixed at one end, caused the motion of pistons placed at the other end. Mr. Farey, a well-known mechanical authority, writing of this scheme of Papin's in 1827, says: It is rather surprising that so simple and advantageous a method of exerting power at a distance from the first mover, should have remained neglected and unnoticed so long as it has been.'

But the more proximate inventor of the system of which we are now treating, was a London mechanical engineer named George Medhurst, who, long before railways were thought of as a general means of conveyance, proposed and described a plan of locomotion by atmospheric pressure, precisely similar in principle to that afterwards used.

His first notions on the subject were published in 1810, when he described his invention of 'New machinery for the rapid conveyance of letters, goods, and passengers by air.' He proposed to enclose letters and papers in a light hollow vessel, so formed as to fill the area of a tube, and to move freely through it; when, by forcing air into one end of the tube, he assumed that he would be able to drive the vessel through the tube at a great velocity. He further proposed to extend the principle by making the tube large enough for a four-wheeled

* Medhurst has sometimes been described as a Danish engineer; but the only explanation to be given for this statement is that he lived in Denmark Street, Soho!

+ Exactly as has been lately proposed by the 'Pneumatic Conveyance Company.'

carriage to run inside it, on an iron road, carrying goods and passengers through the kind of tunnel so formed.

In 1812 he again published a notice of his scheme, but adding the important conception that the necessity of putting the passengers and goods within the tube might be avoided, by substituting a much smaller pipe, the piston of which should communicate by a particular contrivance through the side of the tube' with the carriage outside, and so drag it along. The nature of this 'particular contrivance' he did not, however, disclose till 1827, when, in a third pamphlet, he described various modes of effecting this object. The mode with which we have to do here, introduced, on the top of the tube, a kind of longitudinal flap, riveted along one side, but loose on the other. The piston, running within the tube, had a wheel in front, which, as it passed along, lifted up the flap, forming a slit sufficient to allow a bent rod to pass through from the piston on the inside to the carriage on the outside, so as to give motion to the latter as the former was propelled by the pressure of the air. When the piston had passed, the flap closed of itself, the loose edge falling against a face of leather, or some other soft yielding substance, which made a joint sufficiently tight to prevent leakage under the small pressure the inventor proposed to employ.

Another important step in Medhurst's scheme of 1827 was that he proposed to work his piston both ways— one way by forcing air into the tube behind the piston, or by what may be called the plenum impulse;—the other way by exhausting the air before the piston, or by the vacuum impulse. Taking this latter modification,

we have the perfect anticipation, as far as the idea is concerned, of the atmospheric system subsequently introduced upon railways. The merit of later inventions consisted in the perfection of the details of the apparatus, which Medhurst does not seem to have considered with much care. His invention was probably far too much in advance of the then notions of locomotion to meet with any encouragement for its actual trial.

It is right to mention that the first publication of any proposal for locomotion by Papin's vacuum principle appears to have been by a Mr. John Vallance of Brighton, who, in 1824, re-proposed Medhurst's plan of a gigantic tube, substituting, however, the vacuum for the plenum mode of action.

An agitation was got up at Brighton a year or two later for the trial of Vallance's plan between that town and London. A short trial-tube of the full size was constructed and worked by way of experiment; and it is well remembered how, for want of due precaution in checking the impetus of the carriage, the venturesome experimental passengers were occasionally blown out of the end of the pipe into a field beyond. But this attempt only had the result of furnishing jokes for the pantomimes of the day, and of producing a rather acrimonious paper war between the supporters and the opponents of the scheme. Mr. Vallance does not seem to have known or thought of the much more feasible plan of smaller tubes.

In 1834 Mr. Henry Pinkus, an American engineer, proposed a modified contrivance for opening and closing a slit at the top of the tube, by means of a flexible valvular cord. This was patented in the same year, as

also were other modifications for the same object in 1835; but the proposition appears to have had no practical result, and Medhurst's ideas remained in abeyance until a few years afterwards, when Mr. Samuel Clegg, an engineer well-known for the important part he took in the introduction of gas-lighting, turned his attention to the subject. After studying it well, he adopted Medhurst's general arrangement of a vacuum tube, with a longitudinal slit in its top, but he contrived a form of valve for closing the aperture much superior to any that had preceded it. This was patented by Mr. Clegg, January 3, 1839, and a tract giving an account of the whole system of locomotion thus arranged, and calling attention to its advantages, was published in the same year.

But Mr. Clegg did not work alone in the matter, for, before the date of his patent, he had associated himself with an engineering firm-Messrs. Jacob and Joseph d'Aguilar Samuda, eminent manufacturing engineers of Southwark-who, apparently impressed with the value of the invention, lent it powerful aid, not only by their mechanical and engineering skill, but by the energy with which they advocated its advantages. Messrs. Samuda, in 1844, obtained a supplementary patent for improvements, and through all the experiments and discussions which took place on the subject they were the most active and prominent supporters of the plan.

Soon after the date of the patent, Messrs. Clegg and Samuda laid down at their own premises and elsewhere small model tubes, which answered their expectations; but, not being satisfied with private experiments, they endeavoured to get the system tried actually upon a