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Oldest pitch-drop experiment

Scientists watch the glacial flow of the substance

Physicist John Mainstone (left), who died in August after overseeing the Queensland pitch experiment for 52 years, never saw a fall.

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Grass grows quicker. Paint dries faster. Yet there’s something irresistible about watching the glacial flow of pitch.

And now a long-forgotten experiment with pitch has come to light, probably the oldest known of its kind. In a small display case at Aberystwyth University in Wales sits a glass funnel filled with a heap of ultra-viscous pitch, dated April 23, 1914. That’s 13 years older than a similar setup at the University of Queensland in Australia, which Guinness World Records lists as the longest continually running laboratory experiment.

The allure of pitch — a black tarlike hydro-carbon by-product of distilling petroleum, wood or coal — comes from its split personality: It shatters from a quick hit with a hammer, but flows if set aside for long periods. For more than a century physicists have showcased that contradictory behavior with the pitch-drop and other experiments, in which a seemingly solid mass of pitch displays its liquid nature. At right is a sampling of multigenerational investigations of pitch.

Experiments in flowing pitch

1. Sinking bullets In an 1882 experiment, Scottish physicist Lord Kelvin put corks below and bullets above a block of pitch. Over time the corks floated to the surface and the bullets sank. Pitch was the only earthly material Kelvin knew of that could simultaneously behave as a solid and a fluid. He and other physicists of his era believed that a similar substance called the ether permeated the cosmos. Ether needed to be rigid enough to propagate rapidly oscillating light waves, yet fluid enough for planets and other objects to travel through it. Pitch was a great analog.

2. Kelvin’s ramp In 1887, Lord Kelvin built a glacier-simulating experiment by placing pitch atop a wooden ramp. Over the years the pitch slithered down; today the ramp is on display at the Hunterian Museum in Glasgow.

3. Modern day Physicist John Mainstone (above), who died in August after overseeing the Queensland pitch experiment for 52 years, never saw a fall.

In fact, nobody had ever witnessed a drop of pitch falling until July of this year, when a camera captured a drip in a 69-year-old experiment in Dublin. More than a million people have watched the Dublin pitch-drop video online, while groupies keep an eye on a live webcast of Queensland’s experiment.

4. A new record Despite its head start, the newly rediscovered 1914 pitch experiment in Wales has not produced a single drop. The funnel stem is about 80 millimeters long, Aberystwyth lab technician Stephen Fearn says, yet the pitch has descended a mere 6 millimeters in the century since physicist G.T.R. “Taffy” Evans set it up. At that rate, the pitch won’t emerge from the funnel — let alone form a drop — for another 1,300 years. It’s unclear what type of pitch Evans used and why it flows so slowly.

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