Nine drops in 99 years, and nobody saw one fall

Pitch looks solid: you can shatter it with a hammer. In 1927 the physicist Thomas Parnell melted a little of it at the University of Queensland to show his students that it is actually a liquid. Nine drops have fallen since then, and not one person has watched one fall live.

Parnell poured the pitch into a glass funnel, let it settle for three years and in 1930 cut the stem so it could begin to drip. The first drop took another eight years to come loose. He died in 1948 without witnessing a single fall, and his successor, Professor John Mainstone, looked after the funnel from 1961 until 2013 and never saw one either: in 1988 he stepped out for five minutes to fetch a soft drink and came back to find the drop already down, and in November 2000 the camera he had installed for precisely that purpose broke and recorded nothing.

The ninth drop fell on 24 April 2014 in front of a webcam and of nobody at all. The tenth has been forming for twelve years. Guinness recognises it as the longest continuously running laboratory experiment in the world. There is enough pitch left inside for another long century, and the stuff is some hundred billion times more viscous than water: the drop taking shape right now will be watched by someone who has not been born yet.