From: The Atlantic
by MEGAN GARBER
In 1944, a colleague of Ernest Walton, the first person in history to successfully smash an atom, began an experiment of a decidedly larger and lengthier variety. In a physics lab at Trinity College, Dublin, the experimenter took several lumps of tar pitch -- a hard, carbonic material thought to become viscous under certain conditions -- heated them, and placed them in a funnel. And then placed that funnel into a jar. And then placed that jar into a cupboard.
And then -- after another move of the jar, to a campus lecture hall -- left the thing alone. Not for minutes or days, but for years. And then decades.
The point of this project was to prove that pitch -- which, if you hammer it, shatters like glass -- actually has some liquid properties. It is solid stuff that is, over a looooooooong period of time, capable of flowing. The work (the experimenter who set it up has been, alas, lost to history) examined this phenomenon in a lab setting. And it wasn't the first to do this: the pitch-and-jar setup was a replication of a similar experiment being conducted at the University of Queensland in Australia -- one that, to this day, remains the longest-running laboratory experiment in the world. Both experiments were simple and, in that, wonderfully elegant: their primary component, aside from the tar and the jar, was time. They required little more than waiting and watching.
What made them challenging, however, was this second aspect. Watching, after all, is separate from seeing. And the data the scientists were looking for, for the most part, came in the form of a momentary, yet momentous, happening: the pitch, rendered elastic, succumbing to gravity and leaking through the funnel, dropping to the bottom of the jar. The scientists were waiting-watching for a single, split-second occurrence. It came to be known as the Pitch Drop.