The board was not so easily satisfied and called for an inquiry into the details of Brunel’s plan. The engineer responded to more than 300 questions, often admitting that he hadn’t solved all the design questions, but assuring the directors that he would.

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As Brunel pushed ahead with his ambitious 52-mile line, another short-line Atmospheric Railway had begun operating in January 1846 — the Croyden Railway. Brunel told the directors that the experience gleaned from watching this new line would help him to refine his own scheme, but the first thing he learned was that the Croyden Railway employed a larger vacuum pipe than he had anticipated. Accordingly, he scrapped all the pipe he had already fabricated and ordered it to be replaced with the larger size, taking, in the process, a large bite out of the savings he had claimed he would realize by choosing the atmospheric system over a conventional line.

If there was anything else to be learned from the Croyden line, it was a decidedly negative lesson. While tests of the atmospheric system yielded encouraging results, long-term operation proved very maintenance intensive. The leather seal over the slot in the vacuum pipe caused endless headaches. The leather tended to dry out and become brittle, and when this happened the pipe could not be kept air-tight. The tallow used to keep the leather soft and pliant attracted rats, which nibbled on the seals and did even greater damage. Passengers on the Croyden line often had to push the cars over the track rather than ride in them.

The track-side pumping stations used to create a vacuum inside the pipe caused additional problems. In order for the trains to run properly, air had to be pumped out of each section of pipe before the train arrived, then allowed back in after the train had passed. But it took several minutes of pumping to create the vacuum, and the stations were not connected by telegraph, so the slightest deviation from a set schedule would bring the system to a halt.

Before Brunel could satisfactorily address these problems, service on the South Devon Railway began in May 1846 — using steam locomotives until the atmospheric vacuum tube was completed. More than a year passed before tests of the atmospheric system were scheduled, and several more months before regular service began. Then, within weeks the leather seals on the vacuum pipe began to deteriorate, as they had on the Croyden line.

Brunel even then remained outwardly confident, declaring that ‘Notwithstanding numerous difficulties, I think we are in a fair way shortly of overcoming the mechanical defects and of bringing the whole apparatus into regular and efficient, practical working….’ There seems to have been no real basis for this forecast, however, and by this time even Brunel must have grown desperate as he recognized a failure in the making.

An army of labourers was put to work lubricating and repairing the worn leather seals, but the expense involved put the line into the red, whereas it had earned a tidy sum while it was being worked by steam locomotives. In August of 1848, the last proponent of the Atmospheric Railway finally admitted what had already seemed painfully clear to others, writing, ‘I cannot consider the result of our experience…such as to induce one to recommend the extension of the system.’

Indeed, after the loss of roughly £500,000, the South Devon Railway was converted back into a conventional locomotive railway line. The great ‘Atmospheric Caper’ was over.

This article was written by Bruce Heydt and originally appeared in the May 2004 issue of British Heritage.

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