Atmospheric railways

One of the joys of the internet in general and Wikipedia in particular is that your curiosity can take you along a chain of links to discover new and interesting things.

Last week, for a reason I’ve now forgotten, I wanted to know more about the River Lea, a tributary of the River Thames that meets its more illustrious parent in London’s Docklands. A chain of links that sprang from the Lea’s Wikipedia entry took me eventually to a page about the topic of this blog post: atmospheric railways .

In 1843 Joseph and Jacob d’Aguilar Samuda established the shipbuilding firm Samuda Brothers near the mouth of the Lea. Among the vessels built at Samuda Brothers’ yard was the Fuso, one of the Imperial Japanese Navy’s first armored battleships. Heihachiro Togo , who would later lead Japan’s navy to victory over Russia’s in the Battle of Tsushima, was on hand to observe the ship’s construction, having recently graduated from the Thames Nautical Training College.

But I digress. The Samuda brothers, I learned, were also proponents of atmospheric railways, whose trains are not pulled by fuel-carrying locomotives but sucked along by a vacuum.

The section of disused track shown here gives some idea of how atmospheric railways worked. One of the carriages in the train was equipped with a piston that hung from its undercarriage. The piston fitted snugly inside a pipe that ran between the rails. Ahead of the train, a pumping station created a vacuum in the pipe; behind the train, the pipe was opened, allowing atmospheric pressure to push the piston forward—hence the name.

Thanks to their central pumping stations, atmospheric railways were cleaner than their coal- or wood-fired contemporaries, and lighter. But the technology didn’t catch on. The piston rod that connected the source of the propulsion to the train had to pass through the pipe without losing the vacuum as the train moved forward. Meeting that requirement in the 19th century proved challenging. Moving the trains on and off sidings and onto the mainline was also difficult because of the railways’ closed-loop topology.

Reading about atmospheric railways, I was reminded of a talk entitled “The Energy Problem: What Can a Physicist Do?” that Steven Chu gave at the April 2007 meeting of the American Physical Society in Jacksonville, Florida. At that time, Chu directed Lawrence Berkeley National Laboratory. He became secretary of the US Department of Energy a year later.

In his talk, Chu reviewed progress toward developing energy sources that don’t emit climate-warming gases into the atmosphere. Of all the points he made, the one that has stuck in my mind is the versatility of chemical energy. Unlike the vacuum that propelled atmospheric railways, the chemical energy that fueled steam locomotives was convenient to store and transport.

To catch on, whatever energy source powers the trains and cars of the future will also have to be convenient to store and transport.