To modern eyes the atmospheric railway, with its leather flaps and rats in the pipes, seems a Heath Robinson contraption, but when it was devised by a gas engineer, SamueI Clegg, and the brothers Jacob and Joseph Samuda and patented in 1839 it attracted the serious attention of the brightest brains in the engineering profession.

The idea was to evacuate the air from a tube between the rails, so that the vacuum in front of a piston underneath the train would cause air behind the vehicles to propel them forward at speed, without the weight of a heavy locomotive and the fuel it had to carry.  The slot that admitted the piston was sealed by leather flaps that maintained the vacuum before and after the train passed.

This worked quite well on a 1¾-mile extension of the Dublin & Kingstown Railway in Ireland.  This former horse tramway had an average gradient of 1 in 110, and opened in 1843.

Trains carrying up to two hundred passengers weighing 38 gross tons were propelled by the vacuum in a tube between the running rails at speeds of up to 40mph.

On one occasion the piston carriage set off without its train, and covered the entire line in 75 seconds at an average speed of 84mph.

The London & Croydon Railway ran trains using the atmospheric system between Dartmouth Arms (now Forest Hill) and Croydon from January 1846.

The interior of the pipe was sealed by a mixture of tallow fat and beeswax which melted in hot weather and attracted rats, whose corpses were regularly evacuated each morning.

In frosty weather the leather flaps froze stiff and broke away and snow, instead of rats, got into the tube.

The system was so unreliable that it soon gave way to steam locomotives and the tube was dismantled after May 1847.

Brunel was attracted to the apparent advantages of the atmospheric principle so that he could take the South Devon Railway around the south coast from Exeter to Newton Abbot, where the gradients and tight curves were challenging to contemporary locomotives.

He was unconcerned when questioned about the wisdom of adapting the workings of a 1¾-mile branch line to a fifty-mile main line.

Daniel Gooch, the young locomotive engineer of the Great Western Railway, remarked, “I could not understand how Mr Brunel could be so misled.  He had so much faith in his being able to improve it that he shut his eyes to the consequences of failure.”

The first atmospheric passenger trains between Exeter and Teignmouth ran on September 13th 1847 and to Newton Abbot on January 10th 1848.  The entire service was operated by atmospheric propulsion from February 23rd 1848.

The new system was much admired for the lack of noise, smuts and smoke, and in the first few months barely 1% of atmospheric trains were more than ten minutes late.  A 28-ton train could reach an average speed of 64mph over three miles.

On January 18th 1848, however, cold weather froze the leather and no trains ran until the afternoon.  Increasingly, the leather flaps tore away from their fixings, allowing air leakages to diminish the partial vacuum.  The underpowered steam pumping engines broke down repeatedly and coal consumption was excessive.

Everyone was aware that the London & Croydon Railway had given up on the atmospheric system in May 1847, and through the summer the directors and Brunel himself backpedalled.

The last atmospheric train ran on September 10th 1848.

The most visible reminder of the atmospheric railway is the pumping station alongside Starcross station which was used as a Methodist chapel from 1867 to 1958, while the boiler house became a coal store.

The entire building opened as a museum of the atmospheric railway in 1982 and is now the headquarters of the Starcross Fishing & Cruising Club.

Preparatory work for a road scheme has discovered the remains of a hitherto unsuspected fragment of the pumping station:  http://www.bbc.co.uk/news/uk-england-devon-44099898.

The 36-page, A4 handbook for the 2017 Railways of Devon tour, with text, photographs, maps and a reading list, is available for purchase, price £10.00 including postage and packing.  To order a copy, please click here or, if you prefer, send a cheque, payable to Mike Higginbottom, to 63 Vivian Road, Sheffield, S5 6WJ.

The career of Isambard Kingdom Brunel (1806-1859) is punctuated by two great bridges.  His first major project was the Clifton Suspension Bridge, begun in 1831 but completed posthumously in 1864.  Towards the end of his life he devised and constructed the Royal Albert Bridge, Saltash, to carry the railway across the Tamar into Cornwall.

Throughout his working life his professional rival, Robert Stephenson (1803-1859), was also a close personal friend and ally.

Brunel supported Stephenson at the enquiry into the Dee Bridge collapse in 1847, which first exposed the weakness of long cast-iron girders to support railway locomotives.

The two of them regularly discussed how to bridge wide waterways at height as Stephenson designed the High Level Bridge in Newcastle-on-Tyne (1849) and the box-girder bridges at Conwy (1849) and Menai (1850).

A suspension bridge such as Brunel’s design at Clifton was useless to carry a railway, because the weight of the locomotive would cause the chains to deflect dangerously.

When Brunel took the South Wales Railway across the River Wye at Chepstow in 1852, crossing from an abrupt cliff to a flat flood plain, his solution was to brace the suspension chains with circular tubes.

His great bridge across the wide Tamar estuary, linking Devon and Cornwall by rail, had to leave 100 feet of headroom for passing ships.  Its approaches had to be on curved viaducts.

So his freestanding central spans combine the three classic types of bridge – beam, arch and chain.  He developed the Chepstow design by changing the circular tube to an oval profile, bowed in the form of a convex truss to brace the vertical suspension chains.

Each span was fabricated in turn on the Devonport bank of the river, floated out into the stream and then jacked into position, three feet at a time, as the piers were built.

Brunel conducted the complex positioning of the first, western span in a two-hour process, watched by thousands in complete silence until the Royal Marines Band struck up ‘See the Conquering Hero Comes’ to signal success.

By the time the bridge was finished in 1859 Brunel was so ill that he missed the royal opening ceremony.

He only once saw his great work in its completed state, when he was drawn gently across the bridge in a coach secured to an open rail wagon.

He died on September 15th the same year, and his friend Robert Stephenson followed him a month later on October 12th.  Both of them suffered from what was then called Bright’s disease.

The Cornwall Railway subsequently added the tribute ‘I K BRUNEL – ENGINEER – 1859’ to each end of the bridge.

The 36-page, A4 handbook for the 2017 Railways of Devon tour, with text, photographs, maps and a reading list, is available for purchase, price £10.00 including postage and packing.  To order a copy, please click here or, if you prefer, send a cheque, payable to Mike Higginbottom, to 63 Vivian Road, Sheffield, S5 6WJ.