Early suggestions for atmospheric power
Proposals to use atmospheric power have existed from as far back as the 17th century when Denis Papin (1647 - 1712) proposed a waterwheel driven air pump as a means of generating atmospheric pressure. Further proposals emanated from George Medhurst (1759 - 1827), a Danish engineer, as a proposed system to convey letters at 100mph through a small tube. 1 Medhurst appears to have expanded on his thoughts as in 1812, he proposed twin iron tubes 6ft high by 5ft wide for conveyance of goods or passengers. To cope with the possibility of passengers not being impressed with incarceration inside a dark box, however temporary, he suggested that the carriage be placed outside the tube, a pamphlet produced by him advocated a 12in tube "having a moving box or piston to fit and move freely within side, and made to communicate by particular contrivance through the side of that tube to the carriage without, it will be impelled � by the internal Air." He went to further develop these ideas and 15 years later, he produced 3 further proposals, one of which was a 24in tube laid beneath rails. There would be a 2 inch opening protected by deep flanges and submerged in a trough of water. Compressed air would drive a piston through the tube. As the trough would need to lie flat, he proposed a rise/fall at intervals, using the train's own velocity to bridge the subsequent gap.
Successful development
In Brighton, England in 1826/7, John Vallence constructed a tube of wooden boards with a canvas covering to make it airtight. 150 foot long and c.8 foot in diameter, it contained a carriage 5'6" wide and 22 foot long running on rails within the tube. Air pumps were used to create the necessary vacuum. This was the first successful application of the technology.
11 years later, in 1838, Samuel Clegg & Jacob and Joseph Samuda patented "a new improvement in valves, and the combination of them with machinery". Their work was based heavily on that of a gentleman by the name of Henry Pinkus, an American living in London, whose work was based on that of Medhurst.2
SAMUDA/CLEGG PATENT
The patent obtained suggested the use of a hinge of leather, plated with iron, the lower plate convex to fit the circular tube, sealing composition and a heater, so providing what seemed like a practical solution to the problem of keeping an atmospheric tube reasonably free from leaks.3
The basic principle involved was that of a pipe which would have the air within pumped out, thereby creating a vacuum. As nature abhors a vacuum, anything in the pipe would move along the pipe in an attempt to close the vacuum. If this object was a piston, connected to the outside world through an otherwise sealed opening (apart from the small section necessary to allow this connection), carriages could be connected to the piston and thereby be moved by this act of pumping.
The Samuda's initial experiments were located at their ironworks in Southwark, followed by an experimental line at Wormwood Scrubs in London. But the idea needed a commercial line to prove its point.
Notes:
1. This idea was subsequently developed in the 1850s by Josiah Latimer Clark, an engineer for the Electric Telegraph Company in London as an alternative method of transmission of telegraph messages along specified busy routes. (The Victorian Internet - Tom Standage).
2. There is of course the modern day parallel of Apple Computers having borrowed the idea of the Graphical User Interface (GUI) from Xerox only to become irate when Microsoft successfully developed the idea as Windows �.
3. Hadfield - Atmospheric Railways; David & Charles 1967.
