Cocktail Party Physics

Cocktail Party Physics

Physics With a Twist

A Series of Tubes


Imagine, if you will, a secret community dwelling beneath the streets of New York City, its inhabitants never allowed to travel to the surface or to interact in any way with the dreaded "Topsiders." That's the premise of an award-winning 1999 YA novel by Neal Shusterman called Downsiders, exploring what happens when a 14-year-old Downsider named Talon defies the prohibition and ends up falling in love with a Topsider named Lindsay. Together, they uncover the mysterious origins of the Downsiders: a forgotten inventor named Alfred Ely Beach who created the array of tunnels over a century ago.

This is an instance where science fiction bumps up briefly against science fact, because Shusterman's inspiration for his subterranean world is based on an actual person. Alfred Ely Beach is best known for his invention of New York City's first concept for a subway: the Beach Pneumatic Transit, which would move people rapidly from one place to another in "cars" propelled along long tubes by compressed air. Beach was also the publisher of Scientific American back in 1845, when he purchased it (at the ripe old age of 20) with a fellow investor, so it seems a fitting topic for my inaugural post on that magazine's fledgling blog network. (According to Wikipedia, inventor Rufus Porter actually founded the magazine, but sold it to Beach after a mere 10 months.)

Tunnels and pneumatic transportation systems are a staple of classic science fiction, starting with Jules Verne's Paris in the 20th Century (1863), in which the author envisions tube trains stretching across the ocean. In 1882, Albert Robida described not only tube trains, but pneumatic postal delivery systems in his novel, The Twentieth Century. Those authors were quite prescient: versions of such systems were actually built, and some still exist today.

When I was a kid, I remember my mom using the banking drive-through teller to deposit checks, withdraw cash, etc., through a pneumatic system employing metal canisters. Some of those systems still exist, despite the proliferation of ATMs. Hospitals, factories, and large stores use internal pneumatic transport systems to rapidly move physical objects (drugs, documents, cash, even spare parts) from one location to another. And it all emerged from a vacuum -- specifically, vacuum physics.

Nature Abhors a Vacuum

The first recorded experiments on the existence of vacuum were apparently conducted by an Arab philosopher named Al-Farabi in the 9th century AD, using handheld plungers in water. That's when he realized that the volume of air would expand to fill any available space. Later scientists figured out how to create better and better artificial vacuums, thanks to the principle he delineated. It's pretty simple: by expanding the volume of a given container, pressure is reduced and a partial vacuum is created. It's temporary and is soon filled by air pushing inside by atmospheric pressure, but if the container is repeatedly sealed, the air pumped out, expanded again, and closed off, it's possible to create a sealed vacuum chamber.

Vacuum is measured in units of pressure. Technically, the standard unit of pressure is the Pascal, but scientists can't possibly let things be so simple, so they came up with a new unit for vacuum pressure, the Torr, named after 17th century Italian physicist Evangelista Torricelli, best known for inventing the barometer. He was trying to figure out how to raise water levels in a suction pump to more than 32 feet in height -- the limit pumpmakers had been able to reach using simple suction pumping. It seemed that perhaps Nature truly did abhor a vacuum, but Galileo Galilei cheekily suggested that perhaps the abhorrence only extended to 32 feet. Galileo knew a little something about the weight of air versus other substances, and thought it might be possible to overcome the obstacle using something heavier than water.

Inspired by Galileo's insight, in 1643, Torricelli hit on the notion of using mercury, which is 14 times heavier than water, in a simple experiment: he filled a three-foot-long tube with mercury and sealed it on one end, then set it vertically into a basin of mercury with the open end submerged. The column of mercury fell about 28 inches, leaving an empty space above its level -- an early version of a sustained manmade vacuum. Torricelli further realized that (a) the mercury would rise to the same level regardless of how tilted the tube became because the pressure of the mercury would balance the weight of the air, and (2) the height of the column of mercury rose and fell according to changing atmospheric pressure. Voila! The first barometer.

Seven years later, a German scientist named Otto von Guericke built a contraption known as the Magdeburg hemispheres -- the world's first artificial vacuum. He took two large copper hemispheres with rims that fit tightly together, sealed the rims with grease, and pumped out all the air. To do so, he had to invent a vacuum pump; his version used a piston and cylinder with flap valves, powered by people turning a crank arm that was connected to the pump.

Once all the air was removed from within the hemispheres, they were still held together by the air pressure of the surrounding atmosphere because the artificial vacuum inside provided no opposing pressure to balance things out. It was a pretty powerful hold, too: von Guericke harnessed a team of eight horses to one hemisphere of the big coppery globe, and another eight horses to the other hemisphere, and then set the horses to pulling the two hemispheres apart by moving in opposite directions -- to no avail.

News of the experiment quickly spread throughout Europe, eventually reaching the ears of Robert Boyle, founder of modern chemistry, in England. Few scientists were able to replicate von Guericke's feat because it was an expensive apparatus. But Boyle had the 17th century equivalent of a trust fund, being the son of the Earl of Cork, so he cheerfully set about building his own "pneumatic engine," cost be damned. To do so, he enlisted the aid of Robert Hooke of Micrographia fame, then Boyle's humble assistant. Hooke had a gift for instrumentation, which is a good thing, because Boyle's design was a clunky, difficult to operate device, and sometimes Hooke was the only one who could get the thing to work properly.

Boyle conducted many different experiments to determine the properties of air, specifically how "rarefied air" affected things like combustion, magnetism, sound, barometers, and various substances. He carefully detailed his observations for posterity in a very thick book ponderously titled, New Experiments Physico-Mechanicall, Touching the Spring of the Air, and its Effects (Made, for the Most Part, in a New Pneumatical Engine).

He clearly lacked the gift of catchy titles. Jen-Luc Piquant would have called it something more dramatic, like Asphyxiated! Staring Into the Void of the New Pneumatical Engine.

Suck and Blow

It was only a matter of time before scientists and engineers figured out how to exploit vacuum technology in their inventions, most notably pneumatic tube transport systems to deliver messages or small parcels among various hubs. A Scottish engineer named William Murdoch first conceived of the notion in the early 19th century, and as the century drew to a close, most major cities used some kind of pneumatic tube transport system.

One of the earliest linked the London Stock Exchange to the city's main telegraph station, built in 1853, followed by the London Pneumatic Despatch Company linking the Euston railway station to the city's main post office. Berlin, Paris, Vienna, Prague, Chicago, and New York City all built similar networks, many of which remained operation until the 1950s. The one in Paris was operational until 1984, and apparently the UK House of Commons still has a pneumatic tube system in place for its telephone and computer exchange. And you can find older office buildings in New York with the remains of internal pneumatic mail systems still in place.

Prague's pneumatic post is probably the last surviving such system in the world, housed in an annex to the city's Central Post Office. Completed in 1899, it's a complicated network of pneumatic pipes snaking out through the city's underground for roughly 34 miles. Initially it was used primarily to forward telegrams from telegraph offices to postal offices, but the network was later extended to include government and other office buildings. This came in handy during the notorious Prague Uprising, when the city's pneumatic postal system helped bring supplies to a besieged Czech radio headquarters.

At its peak, in the 1970s, the system made over one million deliveries a year, although that number had fallen to a dismal 6000 or so deliveries per year by 2000 -- hardly a profitable venture, but it's such an unusual piece of Czech history, I'm glad they fought to keep it intact. Alas, massive flooding in Europe in August 2002 damaged the system; it has yet to come back online. Part of the problem is that because the mechanical system has never been modernized, it's tough to find the component parts needed to repair it. (The Berlin factory that used to supply those parts closed down a good 60 years ago.)

Modern pneumatic transport systems can vary in their complexity, but fundamentally, the concept is quite simple. You have a "sending station" -- say, a cashier's checkout post -- linked to a receiving station -- perhaps a locked box in the store manager's office -- via a tube. There is an air compressor pump attached to the tube on the receiving end which has two basic modes of operation: "suck" and "blow."

If you want to send cash from the sending to the receiving station, you'd simply load the it into the metal canister, place it in the tube, and close the door, effectively sealing off the tube. The air compressor would be set to "suck" mode, acting just like your average vacuum cleaner, sucking the air along the tube to create a partial vacuum in front of the canister. The canister can then be emptied, and returned to the sending station via the "blow" mode -- the air compressor literally pushes the canister through the tube by blowing air behind it.

We have more efficient means nowadays of delivering messages (email, twitter, text messaging, etc.) but some folks still think pneumatic tube systems could be useful for, say, delivering food via pipeline. That's the concept behind Foodtubes, a UK-based project that proposes the creation of high-speed pneumatic pipelines connecting every major city in the UK. Food items would be placed in canisters and sent zipping along the nearly 2000 miles of pneumatic tubes. It would be a major capital investment, to be sure, but might cut down on the number of delivery trucks currently clogging up London's roadways.

Such a concept is far from unprecedented: until this year, there was a McDonald's in Edina, Minnesota, that prided itself on being "The World's Only Pneumatic Air Drive-Thru." Customers would place their orders in the drive-thru -- located in the middle of a parking lot -- and their Big Macs, fries, and Chicken McNuggets would be delivered via pneumatic tubes. (One assumes sodas and shakes were delivered this way, too, but the risk of spillage seems rather high.) I'd bet the consortium members are fans of Edward Bellamy's 1888 novel Looking Backward, which predicted a vast interlinked system of delivering goods via pneumatic tubes by the year 2000.

Sub-Rosa Subway

In 1812, a man named George Medhurst speculated that it might be possible to blow carriages laden with passengers through a tunnel, but he never got around to building anything. He lacked a pump with enough power to generate the requisite air pressure. In the mid-1850s, there were several rudimentary "atmospheric railways" -- in Ireland, London, and Paris -- and while the London Pneumatic Despatch system was intended to transport parcels, it was large enough to handle people. In fact, the Duke of Buckingham and several members of the company's board of directors were transported through the pneumatic system on October 10, 1865, to mark the opening of a new station. And a prototype pneumatic railway was exhibited at the Crystal Palace in 1864, with plans to build a version connecting Waterloo and Charing Cross by running under the Thames.

Those early efforts inspired Beach back in the US. He published an 1849 article in Scientific American suggesting building an underground subway along Broadway in Manhattan, employing horse-drawn cars to carry passengers. Then he discovered pneumatics: "A tube, a car, a revolving fan! Little more is required!" he enthusiastically exclaimed. This was way better than boring old steam engines. The idea was to put people in carriages and propel them through underground tubes using air pressure generated by gigantic fans.

He first built a prototype above-ground model, which debuted at the 1867 American Institute Fair. It was little more than large wooden tube (roughly six feet in diameter and 100 feet long) capable of holding a small vehicle with a ten-person capacity, with a gigantic fan on either end. But he couldn't get permission from the city to construct an underground system. (Accounts differ as to whether "Boss" Tweed or wealthy residents blocked his efforts in a 19th century version of "NIMBY" -- "not in my backyard.")

Was Beach at all daunted? He was not. He sneakily built the underground pneumatic subway anyway, pretending he was really building a pneumatic mail delivery system, and he did it right under the nose of City Hall, beneath a rented store front across the street.

In February 1870, Beach unveiled his masterpiece, and it was an immediate novelty attraction for the public, especially given the luxury of the station: it boasted a grand piano, chandeliers, and a fully operational fountain stocked with goldfish. He fought for the next three years to get a construction permit to extend the line uptown all the way to Central Park. Alas, while he ultimately succeeded on that score, a stock market crash (the "Panic of 1873") crushed his dream for good.

Beach's failure didn't keep others from speculating on so-called "vactrains" (vacuum tube trains). The US government considered the possibility in the 1960s of running a vactrain (combining pneumatic tubes with maglev technology) between Philadelphia and New York City, but the project was deemed prohibitively expensive, and was scrapped.

An engineer with Lockheed named L.K. Edwards proposed a Bay Area Gravity-Vacuum Transit system for California in 1967, designed to run in tandem with San Francisco's BART system, then under construction. It, too, was never built. Nor was the system of underground Very High Speed Transportation conceived by Robert M. Salter of RAND in the 1970s to run along what we now call the Northeast Corridor.

Beach might not have lived to see his pneumatic subway system built -- he caught pneumonia and died on January 1, 1896 -- but his vision is still influencing engineers in the 21st century, most notably researchers in the Chinese Academy of Sciences and Chinese Academy of Engineering. Apparently, traveling through networks of these vacuum tubes enables supersonic speeds without the drawback of sonic booms that plague supersonic jets, making the trip from London to New York in less than an hour. (Those of us who are increasingly disgruntled with the airline industry might welcome such an alternative while we're waiting for the physicists to get on the ball with human teleportation.)

And Beach's dream has been immortalized in a song by a Canadian progressive rock band called Klaatu: "Sub-Rosa Subway" (lyrics are here). Nearly three minutes into the tune, you can hear a bit of Morse Code in the background, which one bandmember has since helpfully translated for their fans: "From Alfred, heed thy sharpened ear -- A message we do bring -- Starship appears upon our sphere -- Through London's sky comes spring."

The views expressed are those of the author and are not necessarily those of Scientific American.

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