Papin. - Medhurst. - Pinkus's patent.- Vallance. - Pinkus's first patent Atmospheric railway. - Pinkus's second patent. - Clef's patent Atmospheric railway. - Dalkey line. - Mallett's report on Dalkey line. - Conflicting opinions on the Atmospheric system of traction. - Vignoles. - Cubitt. - Brunel. - Mr. Stephenson's report.- Herepath's report. - Bergin's evidence. - Pilbrow's Atmospheric railway. - Keene and Nickel's Pneumatic railway Hallette's Atmospheric railway Hallette's Pneumatic railway Taylor and Conder's electro-magnetic railway. - Saxton'sDifferential Pulley. - Badnall'sUndulating railway.- Rope friction, Blackwall railway. - Farrill's Patent Archimedean railway. - Parker's Windmill railway.
That mode of propulsion which is effected by Pneumatic pressure, is generally known as the Atmospheric system of railway; from the circumstance of the elastic medium which we breathe being, in most cases, the impelling power. The practical introduction of this system is very recent, and our experience on the subject is consequently very limited. But it has numerous sanguine advocates and partisans; and is now, under variously modified forms, occupying the attention and study of different parties, who are devoting their talents and energies to perfect their several schemes, and bring them into practical operation. We propose first to describe such of the plans as have been carried into effect, and afterwards notice those modifications of the pneumatic principle of motion, which have been suggested as improvements upon the original idea.
The idea of imparting motion to machinery at a distance from the prime mover by the intervention of air, is by no means of recent date. As far back as the close of the 17th century, Papin (for whom the French claim the invention of the steam engine) suggested the plan, and we believe tried it, both by the compression of air, and by its rarefaction, but completely failed. Many years afterwards a trial of the plan was made upon a large scale in Wales, but with no better result, and the plan seems to have fallen into oblivion, when, in 1810, Mr. Medhurst of Denmark-street, Soho, published an account of a "new method of conveying goods and letters by air," followed in 1812 by a prospectus of a plan, by which he endeavoured to prove that goods and passengers might be cheaply and safely conveyed at a rate of 50 miles per hour. To effect this, he proposed to construct an air tight tube of sufficient dimensions to allow a carriage to run within it, and having a pair of cast-iron wheel tracks securely laid along the bottom, for the carriage to run upon.
The carriage was to be of nearly the form and dimensions of the tunnel, so as to prevent any considerable quantity of air from passing by it; and the carriage was to be impelled along the tube by the pressure of air forced into the tube behind the carriage. Supposing the tube to be six feet in diameter, Mr. Medhurst calculated that to produce a speed of 50 miles per hour, would require a constant impelling power of 861 lbs. moving 73 feet per second, which he reckoned as equal to the continual power of 180 horses; and taking the consumption of fuel of a steam engine of that power at 12 bushels of coals per hour, 3 tons of goods might thus be conveyed 50 miles at a cost of 12 shillings, and at a speed of 50 miles per hour.
The plan attracted but little attention at the time, and was for a long period overlooked; but in 1824, Mr. Vallance of Brighton obtained a patent for a similar invention, with this difference, that he proposed to exhaust the air in the tube in the front of the carriages, instead of forcing it in behind them as in the plan of Mr. Medhurst. Mr. Vallance subsequently constructed a short tube id his garden at Brighton, to demonstrate the practicability of the plan, and mention was occasionally made in the public prints of experimental trips which had taken place; but the apparatus was not of sufficient extent to show forth either the difficulties of the plan, or the extent to which they would be overcome; and this scheme, like the previous one of Mr. Medhurst, was never carried into effect.
The most obvious objection to the plans we have just described, is the necessity for the passengers to travel within the tube, excluded from daylight, and this alone would have been sufficient to prevent their ever being acted upon. This objection was first overcome by Mr. Pinkus, who by thus bringing the plan within the sphere of feasibility, may be considered as practically the inventor of the Atmospheric railway. His plans, it is true, have not been adopted in all their details as originally proposed by him, but, variously modified, they form the basis of the most promising schemes which have since been brought forward for propelling by the pressure of the atmosphere. Mr. Pinkus's first plan, and for which he obtained a patent in 1834, is fully described in the first part of the Encyclopedia, under the article "Air;" it will be sufficient therefore in this place to say that it consisted of a tube laid down between a pair of rails on which the carriages were to run, and having on the top of it a longitudinal groove extending throughout its length. Within this tube was a piston, attached to the leading carriage of the train by an arm passing through the groove.
This groove was closed by a thick cord, saturated with a composition of wax and tallow, in order to form an air-tight joint throughout the length of the tube, except at the part where the piston arm projected through the slit, where it was raised out of the groove by rollers attached to the arm, so as to leave an opening for the admission of the air into the tube, at the back of the piston. The tube in front of the piston was connected with an air pump, and a partial vacuum being formed in the tube, the pressure of the atmosphere upon the back of the piston would propel it along the tube, and with it the carriages connected to it.