In 1836, Mr. Pinkus took out a patent, for his second plan of atmospheric propulsion, which differs materially from his first, the travelling piston in the atmospheric main being dispensed with, and the system in some measure assimilated to the locomotive system. The following is a description of the plan, nearly as given in the Mechanic's Magazine: - A tube is laid down between two lines of rail, and communicates with air pumps placed along the line, which act upon the air in the tube, continually rarefying it as it is thrown in by the working of the locomotive apparatus. The main has an opening in the upper surface, two inches wide; on to the edges of this opening are attached plates, forming what Mr. Pinkus calls a metallic valve, made of an amalgam of iron and copper, hard rolled to make it elastic, l-8th, of an inch thick at the lower edge, and 1-16th at the upper, (the insides of which are to be polished smooth,) and four inches high. The annexed cuts will show the thing more clearly. Fig. 1 is a plan of the valve, and Fig. 2 a cross section of the air main with the valve attached, and the tongue (afterwards described) between the lips of the valve.
In both Figs. a a are the lips of the valve, which it will be seen, in their undisturbed state, by their elasticity press upon one another, and form an air-tight joint the whole length of the main. Working between the lips of this valve, is a hollow metallic tongue (b Fig. 2), the shape of which is seen in Fig. 1. The sides of this tongue in contact with the lips of the valve are polished, and the tendency of the latter to collapse, by their spring pressing upon these polished sides as they pass along, makes the joint air tight. This hollow tongue forms a communication through throttle valves, with a condenser or vacuum vessel, and this vacuum vessel communicates, through alternating openings, (somewhat similar to those used in steam cylinders, and worked by an eccentric from the crank,) with two cylinders in which work pistons, whose rods turn cranks which give a rotary motion to the wheels of the locomotive. The mode of action is as follows: the air in the main is kept rarefied by the exhausting engines at each end; a communication being made between it and the rarefied air or vacuum vessel by opening the throttle valve, and between the vacuum and the cylinder by the sliding passage, a partial vacuum is formed under the piston, which the outward atmosphere forces down, giving half a turn to the crank; the alternating air passages are then reversed, the other piston is acted upon in the same way, and a revolution of the crank and consequently the carriage wheel is completed.
The cylinder full of air, after having forced down the piston passes into the vacuum vessel, and through the hollow tongue into the main, from which it is pumped into the atmosphere by the stationary engines and air pumps at each end of the five mile section. As the tongue passes forward, it will open a passage for itself between the lips of the valve, which will immediately close behind it by the elasticity of the plates. The tongue is prevented from becoming hot by friction, by the current of cold air constantly passing through it from the cylinders.
Although this scheme manifests considerable ingenuity on the part of the inventor, we think it upon the whole inferior to his first plan. In particular we would notice that the advance of the train depends upon the adhesion of the wheels of the propelling carriage to the rails, so that in unfavourable states of the rails, the wheels would be liable to slip, and also the power of ascending inclines would be diminished, as on the present system of traction by locomotive steam engines, whereas by the first plan, provided a sufficient pressure could be produced at the back of the piston to overcome the friction of the load and the power of gravitation, the train must advance whatever be the state of the rails, or the steepness of the incline.
Mr. Pinkus endeavoured to form a public company, to carry his invention into effect, but did not succeed in so doing. His efforts however had the effect of drawing public attention to the subject, and provoking discussion; and paved the way for Mr. Clegg, who in 1839 took out a patent in connexion with the subject, and eventually succeeded in procuring its adoption by a company, and who may therefore be considered in one sense as the introducer of the Atmospheric railway. The title which Mr. Clegg selected for his patent was chosen very skilfully, and, although it certainly may be said to cover the invention, could at that period scarcely be supposed to refer to railways, and was therefore little likely to meet with opposition from parties who were directing their attention to that subject. The title is for a new improvement in valves, and the combination of them with machinery; but it will be seen that the improvements do not refer to valves in general, but solely to a continuous valve for the purpose of Atmospheric railways; the following is an extract from the specification:-
"My improvements consist in a method of constructing and working valves in combination with machinery. These valves work on a hinge of leather, or other flexible material, which is practically air tight, similar to the valves commonly used in air pumps; the extremity or edge of these valves is caused to fall into a trough, containing a composition of bees'-wax and tallow, orbees'-wax and oil, or any substance or composition of substances which is solid at the temperature of the atmosphere, and becomes fluid when heated a few degrees
Fig. 2 above it. After the valve is closed and its extremity is lying in the trough, the tallow is heated sufficiently to seal up or cement together the fracture round the edge or edges of the valve, which the previous opening of the valve had caused, and then the heat being removed the tallow again becomes hard, and forms an air tight joint or eement between the extremity of the valve and the trough. When it is requisite to open the valve, it is done by lifting it out of the tallow, with or without the application of heat, and the before named process of sealing it or rendering it air tight is repeated every time it is closed. This combination of valves with machinery is made in the application of these valves to railways, or other purposes of obtaining a direct tractive force, to move weights either on the railway or otherwise. This I effect by laying down a continuous length of pipe, containing a lateral slit or opening its whole length: a piston is made to travel in this pipe by exhausting or drawing out the air from the pipe on one side of the piston, and allowing free access to the atmosphere on the other side of it; an arm from this piston passes through the lateral opening, to attach to the carriages on the railway, and draws them along with it.