In the year 1810, Mr. Medhurst took out a patent for conveying letters and goods by the pressure of air; and shortly afterwards he issued a prospectus, to show the practicability of conveying persons and goods with ease and safety at the rate of fifty miles an hour. The plan was to propel a carriage through a long tube or tunnel, by forcing air into the tube behind the carriage; these two parts being made so nearly to fit that very little air would escape past the carriage. No attempt, that we have heard of, was made to carry out this scheme; but in 1824, Mr. John Vallence obtained a patent for a different mode of applying the air as a means of transport. Instead of forcing the air at the back of the carriage, he exhausted the tube in front of the carriage or train, and allowed the natural pressure of the atmosphere to operate at the back. This arrangement appeared more feasible than Mr. Medhurst's; and we have heard that Mr. Vallence set up a large model in his garden, to demonstrate the practicability of his plan; the eligibility, however, of travelling through a continuous tube was not satisfactorily shown, and it shared the fate of its precursors. The last-mentioned objection was subsequently completely obviated by Mr. Henry Pinkus, a highly ingenious American gentleman.

His invention consists in transferring the action produced upon a piston or diaphragm, moving in the interior of a tunnel or tube, to its exterior, by connecting a vehicle or machine, (termed the dynamic traveller,) situated within the tube, with a car or carriage without, (denominated the governor,) to which the train of transport carriages is attached. The pneumatic railway admits of several methods of application, in each of which the dimensions, economy, and details, vary. It will be sufficient in this place to describe one, in doing which, we shall avail ourselves of a condensed extract from the specification.

" The length of the pneumatic tube will be equal to the whole length of the railway or canal to which it may be applied, and it should be cast in portions of the greatest length possible, in smooth metal moulds, so that their inner sides should be very even and true, and they are to be connected by the ordinary socket joint. Fig. 1 of the annexed wood-cuts exhibits a perspective sketch of a portion of a line of pneumatic railway, laid down, exhibiting the ' governor ' drawing a train of carriages along it. The upper half only of the air tunnel a a is seen, the other half being imbedded in a semicircular trench; on the edges of which trench rest strong projecting ledges, which are cast to the outsides of the tunnel, in a longitudinal direction. These ledges are about three inches wide on their upper surfaces, and constitute the railway upon which the wheels h h of the governor or drag, and those of the train, run. To explain the mode adopted of communicating the motive force generated in the interior of the tunnel to the governor on the outside, we must refer the reader to Fig. 2, which represents a sectional perspective of a portion of the tunnel; wherein it will be seen that a strong flat bar f is bolted to the governor, so as to depend vertically through a longitudinal chase made in the top of the tunnel, and reaching to the centre of it.

Here it is firmly fastened to a species of carriage, of the form of a velocipede, which operates as a guide and stiffening-frame to the piston or diaphragm c, that receives the impulse of the atmosphere; the expanding piston having a conical steel ring around its periphery, one foot wide, and placed at an angle of about 15° from the surface of the cylinder, against which one edge of the cone acts with a slight pressure of the air, so as to conform to any slight inequality of the cylinder. A more exact comprehension of these arrangements will be afforded by the subjoined Fig. 3, which exhibits a transverse section of the pneumatic railway; an end elevation of the governor, its connexions and position; also the rear wheel of the dynamic traveller; its position within the cylinder; the guide rail (cast to the interior of the cylinder) on which it runs; and the piston in advance, a a a is the cylinder, the lower semi-circumference of which is of greater thickness than the upper, to enable it to withstand the greater strain on this part, to which it is subjected by the weight of the carriages rolling upon the projecting ledges or rails b b; ccc shows the area of the piston strengthened by cross bars; dddd stay rods, connecting the piston to the frame of the dynamic traveller. the hind wheel only. e. of which can be seen in this view. f exhibits an edge view of the bar that connects the dynamic traveller to the governor g, of which h h are the running wheels, connected by a cranked axle-tree. .In connexion with the vertical arm f are inflexible horizontal arms, from which are suspended by pivots or vertical axles anti-friction wheels i i, whose peripheries roll on the outer sides of the longitudinal chase, and keep the vertical arm in the centre, so as to prevent its touching on either side.

This figure also shows the shape of the longitudinal chase or aperture, through which the connexion is made from the interior to the exterior; this chase is cast with the cylinders, and is necessarily continued the whole length of the tunnel. In order that the running wheels of the governor, as well as those of the train of carriages that follow it, may be kept truly upon the centre line of the projecting rails, and never rub against the sides of the tunnel, metallic arms are projected from their frames, carrying anti-friction wheels, the peripheries of which roll against the outer sides of the longitudinal chase and underneath the flange: this latter circumstance affords a great security against upsetting. And for the purpose of keeping the peripheries of these anti-friction wheels always in contact with the chase, whatever curves may be made in the line of railway, their axles turn in slots, and are pressed inward by springs. Into the trough, an elastic flexible padded chain, called by the patentee, the valvular cord, is fitted the whole length of the tunnel, forming, as it were, a continuous valve. In the annexed figure, this valve is shown in section on a greater scale, with the flexible cord l in its place.