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Atmospheric and Pneumatic Railways

The ultimate responsibility for this topic :-) belongs to George Medhurst (1759-1827), of England. During a period of a few years about 1810, he invented three distinct forms of air-propelled transport. None of them was implemented during his lifetime; but all of them saw use eventually, reaching their greatest extent in the reverse order of their original invention.

Medhurst's first method involved moving air through a tube a few inches in diameter, pushing a capsule along it; this simple idea was the pneumatic dispatch tube. Next he realized that if the same system was built much larger, it could carry passengers (or freight items larger than letters); it was natural to run the vehicle on tracks, and so this became known as a pneumatic railway.

But would anyone actually want to ride along mile after mile inside an opaque pipe? Not likely. So he then thought of having only a piston moving within the pipe, somehow dragging along a vehicle outside it. He proposed several versions of this idea; in most of them the vehicle ran on rails, so this became known as an atmospheric railway (though a distinction between that term and the pneumatic railway was not always observed). The key feature of all versions of the system was a longitudinal valve: some sort of flexible flap running the length of the pipe, which would be held closed by air pressure except when the piston was actually passing. Medhurst did try to raise capital to implement this system, but failed.

Now, while the first operable steam locomotive was built about 1804, steam-powered trains did not see regular use for passengers for some 25 years after that. It was in the 1830's and 1840's that the steam railway was shown to be practical in both engineering and financial senses.

But the same technical developments that made possible the practical steam railway also made the atmospheric railway, if not certainly practical, at least worth a try. And it offered the prospect of considerable advantages. Since the trains wouldn't have to carry their prime mover, they would be lighter; therefore the track could be built cheaper, and the trains' performance would be better. The trains wouldn't trail smoke wherever they went (and into the passenger cars in particular), and they would also be quiet. And if one section of the route was hilly and required more motive power, all that were needed would be more or larger pumping stations along that section; no need to add extra locomotives. In short, very much the same advantages that electricity gave a few decades later. (Plus one more: a derailed train would tend to be kept near the track by the pipe and piston.)

The success of the 1830's railways gave rise to the Railway Mania of the 1840's, when interest in railway shares reached absurd levels. In that climate the proposers of atmospheric lines could find the backing they needed, and four atmospheric lines opened in a period of about 3 years. In order of opening, these were:

• The Dublin & Kingstown, from Kingstown to Dalkey in Ireland, 1.5 miles long; operated 1844-54.
• The London & Croydon, from Croydon to Forest Hill in London, England, 5 miles, then extended to New Cross for a total of 7.5 miles; operated 1846-47.
• The Paris & St-Germain, from Bois de Vezinet to St-Germain in Paris, France, 1.4 miles long; operated 1847-60.
• The South Devon, from Exeter to Teignmouth in Devonshire, England, 15 miles, then extended to Newton (now Newton Abbot), 20 miles altogether; operated 1847-48.

I note in passing that while I (as a fan of his) might like Isambard Kingdom Brunel to have invented the atmospheric system used on the South Devon, it is wrong to say that he did so, as is sometimes done. He did choose it for the line and actively promoted it (well, "actively" is redundant with Brunel). It was actually developed by Samuel Clegg and Joseph and Jacob Samuda.

Both of the longer, if shorter-lived, English lines used atmospheric propulsion in both directions of travel, whereas the French and Irish lines were built on hills and their trains simply returned downhill by gravity. Since all were single-track lines, the one-way system simplified the valves needed to let the pistons in and out of the pipes at their ends (possibly while traveling at speed).

All four lines were converted to ordinary steam railways in the end. For one thing, steam locomotive technology had too much of a head start in development over the atmospheric system; steam railways might have delays due to engine failure but they never had to shut down for 6 weeks while a new design of longitudinal valve was installed along the entire length of the route!

(The valve involved metal and leather parts and a greasy or waxy sealant "composition". Although stories were told about rats eating the composition, and this probably did happen sometimes, it wasn't really a serious thing; the biggest problems in fact were freezing and deterioration of the leather, and corrosion of the metal parts.)

Also, the atmospheric system was inflexible, in that if the power requirements for a section of route were greater than estimated, very little could be done short of splitting the section and adding a whole new pumping station. (All the lines used vacuum rather than positive pressure in the pipes, which limited the pressure differential to about 0.9 atmosphere in practice; but the valve designs were marginal anyway and likely wouldn't have stood up to greater pressures if they could have been used.)

What today might be seen as the most serious disadvantage of all, the requirement for long interruptions of the motive power at junctions, was not so noticeable in those days. If the train didn't have enough speed to coast across the gap, well, the third-class passengers could always get out and push, or maybe there would be a horse conveniently at hand. At some stations a small auxiliary pipe was used to advance the train from the platform to the start of the main pipe.

There were many other proposals in those days for atmospheric lines, but in view of these early failures, none of them were ever built as atmospheric railways, and the atmospheric system appeared dead. In fact, it was nearly 130 years before another atmospheric railway appeared!

While the first atmospheric railways were vanishing, the first pneumatic dispatch tubes were beginning to appear; I'll get into that later. But from that start, the pneumatic railway idea began to return also. At first these were designed for freight. Engineers J. Latimer Clark and T. W. Rammell formed the Pneumatic Despatch Company, which built a demonstration tube above ground in Battersea in 1861. This line successfully carried loads up to 3 tons... and even a few passengers, lying down in the vehicles in the 30-inch pipe! With the large pipe and small vehicles, a much lower pressure could be used, no more than 0.025 atmosphere. Vehicles ran on a 2-foot gauge track formed right into the tube segments, and speeds up to 40 mph were reached.

When the Post Office became interested in the system, the company built a tunnel from Euston station north about 1/2 mile to the PO's North-West District Office, reusing the tube segments from the Battersea demonstration. This entered service in 1863 and was used until the financial crisis of 1866.

A second line more than 2 miles long was built, south and east from Euston to the General Post Office near St. Paul's. This used a tunnel 4 feet wide, containing track of gauge 3 feet 8.5 inches; The end-to-end time was 9 minutes.

The Pneumatic Dispatch Railway, as it became known, operated until 1874, but at this point the Post Office decided that the time saving wasn't worth the cost, not to mention the risk of a vehicle becoming stuck in the tube. The tunnel was later interrupted in places by Underground construction, but the surviving segments saw some use as utility conduits. However, gas tended to leak into them; and one day in 1928, a workman apparently used a match to see where to plug in a fan to blow the gas out, and instead blew it *up*, over a half-mile length of tunnel.

(In the 1920's, when electricity was available, London got a new driverless train system with similar sized tunnels to the PDR's. This Post Office "tube" Railway, later renamed MailRail, continues in use today. Such systems also exist in Switzerland, which had it first, and in Germany.)

Meanwhile, while these lines were moving the mail from the streets of London to tunnels underneath, the first underground railways were doing the same with passenger traffic. The first section of the Metropolitan Railway (from Farringdon, now Farringdon Street, to Paddington station) opened in 1863. It was promptly followed by extensions, as well as competition in the form of the Metro- politan District Railway, a subsidiary that got away. (Their routes in central London today form the London Underground's Metropolitan, District, Circle, and Hammersmith & City Lines.)

Now there was no thought of operating the Metropolitan with anything but steam locomotives, despite the line being mostly in tunnel. Sir John Fowler, who later co-designed the Forth Bridge, did have the idea of a steam locomotive where the heat from the fire would be retained in a cylinder of bricks, and therefore the fire could be put out when traveling in the tunnels. One example of this design, later called Fowler's Ghost, was tried in 1862. It was thermodynamically absurd: as C. Hamilton Ellis put it, "the trouble was that her boiler not only refrained from producing smoke, it produced very little steam either".

In the end both the Met and the District were worked with condensing steam locomotives: these emitted smoke as usual, but their exhaust steam, while running in tunnels, was directed back into the water tanks and condensed. The tanks were drained at the end of the run and refilled with cold water.

So people were not only willing to travel in what amounted to an opaque tube after all, but in one filled with smoke at that! (The smoke problem was bad enough on the Met that they arranged for ducts to take air from the PDR's line where they crossed; later they built "blowholes" from the tunnel into the street. Neither helped much.) But then why not a tube *without* smoke? And so the pneumatic railway was now tried; but it never got past the demonstration stage.

The longest line to carry passengers was opened at the Crystal Palace in London in 1864. It used a tunnel about 9 by 10 feet, 1800 feet long. The driving fan was 22 feet across, generating about 0.01 atmosphere of pressure -- the larger the tube, the lower the pressure you need. The vehicle was a full-size broad gauge railway car ringed with bristles; it carried 35 passengers. The trip took 50 seconds, thus averaging about 25 mph. Another, smaller demonstration line was built at a fair in the US in 1867 by Alfred Ely Beach, the publisher of Scientific American.

Beach then formed the Beach Pneumatic Transit Company, which obtained permission to build a freight-carrying pneumatic line under Broadway in New York. But what he actually opened in 1870 was a passenger-carrying pneumatic subway, the only one to actually operate under a city street. It was only 312 feet long, from Warren Street to Murray Street. The tunnel was 9 feet in diameter, and was worked by a single car with a capacity of 18 passengers.

Beach tried but failed to get permission to extend the line. It closed after some months, and New York did not get a subway again until 1904.

In London, a pneumatic underground line was started *with* permission, but construction was never completed. This was the Waterloo and Whitehall Railway, which planned to connect Waterloo station to Great Scotland Yard, 1/2 mile away, with a 12'9" diameter tunnel passing under the Thames. Considering that the Thames Tunnel project of Sir Marc Brunel and Isambard Kingdom Brunel -- now now part of the Underground's East London Line -- had faced massive technical and financial difficulties before its long-delayed completion only about 20 years previously, this was no mean undertaking.

The Waterloo & Whitehall was halted by the financial crisis of 1866; and it was never revived. The tunnel had been started from the Great Scotland Yard end, and had just reached the river; work on the underwater section was beginning. There were other proposals for passenger-carrying pneumatic lines, but none saw construction in that form. (At least one, under the Mersey at Liverpool, England, was eventually opened as an ordinary railway. Before electrification it used condensing steam engines like the Metropolitan Railway's.)

The next type of underground line to open in London was the Tower Subway, which also passed under the Thames. It was a short route, just under the river, worked by a small cable car. It opened in 1870 and was short-lived. (The tunnel served as a footway for a while after that, then was taken over for utilities after the Tower Bridge opened in 1894. The Thames Tunnel, conversely, had been used first as a footway, then converted to railway use.)

After this time, electric railways began to become practical. The next underground line to open was the City & South London, now part of the Underground's Northern Line. Its first section (from Stockwell to a now disused terminus at King William Street, replaced by the present Bank station) opened in 1890. It used the new deep-level tube tunnels, with more limited ventilation than on the Metropolitan Railway, so steam was out of the question in any case. The original plan was for cable haulage, but instead the new electric locomotives were tried and the line has always been operated electrically. The line was first built with tunnels as small as 10'2" diameter, forcing use of rather small cars. (The cars also had only tiny windows, on the grounds that there was nothing to see -- so they got the nickname of "padded cells".)

All of the later lines that went into the London Underground system, opened from 1898 onwards, were built on the same general pattern as the C&SL, with deep-level tubes and electric traction -- usually by multiple-unit trains, and the two lines that used electric locomotives were later converted. The tube lines were generally built with tunnels of 12 feet diameter or a little smaller; the two lines that were under 11'8.25" diameter were enlarged in the 1920's and 1930's to that minimum. This is still rather small compared to most other subways in the world, and gives the tube trains their distinctive shape.

With the success of the electric lines, the Metropolitan and District faced the loss of traffic, and they too were converted to electricity -- at least for the underground sections in central London -- in 1905. The first line of the present New York subway system opened in 1904 and this, too, has always used electricity. (This was the original Interborough Rapid Transit route, from City Hall station along the present Lexington Avenue, 42nd Street shuttle, and 7th Avenue lines, initially as far as 145th Street). Beach's tunnel had been almost forgotten when the crews constructing a new subway line there broke into it in 1912.

Meanwhile, the humble original concept of the pneumatic dispatch tube continued to develop. The first of them, 1.5 inches in diameter, had been built in 1853 by J. Latimer Clark; it connected the Electrical and [sic] International Telegraph Company's office in Telegraph Street, London, with their branch 675 feet away at the Stock Exchange.

The key invention was J. W. Willmott's double sluice valve of 1870, which allowed rapid dispatching of successive capsules. It was also possible, as had been done on the pneumatic railways, to use both positive pressure (on the order of 1 atmosphere) and vacuum, to drive the capsules both ways from a single pumping station. The tubes became quite common; many miles were built in various European and North American cities. By 1886 London had over 34 miles of them for the Post Office's telegraph service alone. The New York post office system, which operated 1893-1953, eventually had east side and west side tubes running for most of the length of Manhattan. In Paris, a person could pay a fee for a message to be sent specifically by the tube; such messages were sometimes called pneumatograms.

Pneumatic dispatch tubes were also used within large buildings, or between a main building and outbuilding, and some survive in such uses to this day. Since they can carry small packages, one important use of them has been for transporting money, between a cashier and central office. Methods for automatic routing to different destinations were developed; in one system, each capsule carried one of several different reeds so that it made a musical note as it advanced through the pipe, and a sound detector switched the pipe according to the note.

As well as the atmospheric and pneumatic railways and their cousin the pneumatic dispatch tube, there was a fourth way that air pressure was used to move people or freight. In this design, rather than a compressed-air or vacuum pipe running the length of the route, the vehicles themselves carried a compressed-air reservoir. Air from the reservoir was simply used to drive cylinders in the same fashion as the steam from the boiler of a regular locomotive.

A few streetcar lines were operated on this system in both Europe and the US. The French city of Nantes adopted it on a large scale, building a whole fleet of compressed-air streetcars that ran from 1879 to 1917. One of the later models, of which 148 were built starting in 1900, was charged with 530 pounds weight of air compressed into about 95 cubic feet: 80 atmospheres of pressure. The compressed-air storage was under the floor, and the air had to be heated before use, to keep the cylinders from freezing up.

But the major niche for this form of compressed-air power was in indus- trial applications such as mines, where fire was a major hazard and compressed air was already in use for other purposes but steam was not. (Steam was more convenient, since you can get more of it at the same pressure from the same size pressure vessel by filling it with boiling hot water.) Compressed-air locomotives for this purpose lasted so long that I wouldn't be surprised to hear that a few are still in use today.

As mentioned above, in the late 20th century the atmospheric railway reappeared. In 1983 in Porto Alegre, Brazil, an aviation engineer named Oskar Coester constructed a demonstration line with unmanned vehicles. In 1987 he joined the Sur Elevator company in a partnership called Sur Coester; they market the system under the name Aeromovel. And they have had a line in service at a fairground in Djakarta, Indonesia, since December 1989.

This line is 2 miles long, elevated, on a concrete structure. The cars use steel wheels on steel rails. The air pipe is rectangular, made of concrete, and larger than those on the 19th century lines. The longi- tudinal valve is made of heavy cloth-reinforced rubber. The vehicles are controlled remotely by computer.

In January 1997, an educational program on the BBC called Local Heroes showed the construction of a miniature atmospheric railway, powered by a vacuum cleaner. A simple 2-inch cardboard tube was used first as the pipe, and this turned out to be flexible enough to seal itself, needing no longitudinal valve at all. When a 6-inch tube was tried, a line of Post-It notes sufficed to form the valve. Young viewers were invited to try the experiments themselves. Of course, these constructions did not need to stand up to the weather.

Oh yes.

Pneumatic dispatch tubes were depicted in the 1985 movie "Brazil"; Beach's tunnel was depicted, in rather distorted form, in the 1989 movie "Ghostbusters II"; the modern form of the New York subway has been depicted in many movies, notably the 1974 one "The Taking of Pelham One Two Three"; but I don't believe the atmospheric or pneumatic systems have ever been depicted at work in any movie. Clearly this needs to be rectified! :-)

References and credits

Almost all the information in this posting about the pneumatic and atmospheric systems comes from one book... "Atmospheric Railways: A Victorian Venture in Silent Speed" by Charles Hadfield, 1967, reprinted 1985 by Alan Sutton Publishing, Gloucester, England; ISBN 0-86299-204-4.

The information on the Nantes compressed-air streetcars is from the Musee des Transports Urbains at Paris. The information about Aeromovel comes from net postings by Andrew Waugh (citing the November 24, 1990, issue of "New Scientist" magazine), Russell Day, and Jerry Schneider. The BBC information was found on their web site. The information on the PDR is mostly from an article by Roger Cline in the September 1993 issue of Underground News (published by the London Underground Railway Society).

For other topics, I principally consulted "The Pictorial Encyclopedia of Railways", 1976 edition, by (C.) Hamilton Ellis, Hamlyn Publishing; ISBN 0-600-37585-4. Some details came from other books or my memory.