In a glass display case at the University of Queensland in Brisbane, a black bulb of pitch hangs from the stem of a glass funnel, slowly stretching under its own weight. The funnel’s stem was cut open in 1930. Ninety-six years later, only nine drops of pitch have been counted, and the university still expects the tenth sometime in the 2020s.
The setup is disarmingly simple. A funnel. A beaker. A lump of pitch, a derivative of tar once used for waterproofing boats. At room temperature it feels solid and brittle enough to shatter under a hammer. Leave it under gravity for long enough, however, and it flows.
A physics demo that outlived its inventor
Thomas Parnell, the University of Queensland’s first professor of physics, set the demonstration up in 1927. According to the experiment’s original published account, he warmed the pitch, poured it into a glass funnel with a sealed stem and allowed it to settle for three years.
In 1930, the sealed stem was cut. That is when the long record of falling drops began.
The first did not fall until December 1938. The second followed in February 1947. Parnell died in 1948, having lived long enough to see evidence of two drops from an experiment that would continue for generations after him.
How thick is pitch, really?
Pitch at room temperature is extraordinarily viscous. It resists flow so strongly that the movement happening inside the funnel is almost impossible to detect over ordinary human timescales.
A drop can take years to accumulate, stretch downward and eventually separate. That is the point Parnell wanted to make: something that looks and feels solid during a classroom demonstration can still behave as a fluid if enough time is allowed.
The experiment turns an abstract property into something visible. The pitch does not suddenly become liquid. It has been flowing all along, simply at a rate that makes ordinary patience seem absurdly short.
The nine drops
The recorded drops came in 1938, 1947, 1954, 1962, 1970, 1979, 1988, 2000 and 2014. The first several arrived roughly seven to nine years apart, while the eighth and ninth took much longer.
The experiment is not kept in a tightly controlled laboratory environment, so temperature matters. Changes to the conditions around the display over the decades, including air conditioning, have affected how quickly the pitch moves.
The ninth drop created another complication. It descended until it reached the older pitch in the collection beaker, and the original beaker was subsequently removed. The UQ Physics Museum records that the beaker containing drops one through nine now sits beside the experiment and that a fresh beaker has been placed beneath the tenth drop.
That detail matters. The black mass now forming beneath the funnel is not resting on the ninth drop or on the old pile. It hangs above an empty collection beaker, giving the next drop room to fall freely.
Nobody has ever seen a Queensland drop fall
This remains the strangest part of the University of Queensland experiment. Across almost a century of waiting, no human being has directly witnessed one of its drops detach and fall.
Thomas Parnell missed them. So did John Mainstone, the physicist who became the experiment’s second custodian in 1961 and looked after it for 52 years.
Mainstone came especially close in 2000. Recording equipment had been trained on the experiment, but a power interruption meant the crucial moment was missed. By the time the system was operating again, the eighth drop had fallen.
Mainstone died in August 2013. The ninth drop reached the previous pitch the following April, and later that month it separated from the funnel during the operation to replace the crowded beaker. He never saw one fall.
The current watch
Professor Andrew White is the third and current custodian. The experiment remains on public display, and UQ also provides a live video stream for anyone willing to join the wait.
The tenth drop now hangs above the fresh beaker installed after the events of 2014. Nobody at UQ claims to know exactly when it will separate. The university’s public estimate remains simply that it is expected sometime in the 2020s.
If the moment is successfully recorded, it will finally give Queensland footage of one of its own drops separating. It would not, however, be the first pitch drop ever caught on camera.
Dublin caught what Queensland missed
Another long-running pitch experiment began at Trinity College Dublin in 1944. In 2013, physicists there put the apparatus under webcam observation as another drop approached separation.
On July 11 that year, the drop fell and the camera captured it. Trinity described the event as the first time the phenomenon had been witnessed on video. The scientists themselves were not standing over the apparatus at the instant it happened; the recording preserved what human attention had missed.
Queensland is still waiting for the equivalent moment from Parnell’s original demonstration.
Why bother?
The pitch drop is primarily a demonstration, but it is not literally devoid of scientific data. The published 1984 analysis used the volume of pitch that had flowed during the first six drops to estimate its viscosity.
Modern instruments can characterise viscosity vastly faster than waiting years for a single drop, so that is no longer the experiment’s main value. Its lasting power is visual. It takes a physical property that sounds abstract and stretches it across a human lifetime.
That makes the experiment unusually effective as a lesson in timescale. Some processes are easy to miss not because nothing is happening, but because the change occurs too slowly for the eye to register from one moment to the next.
The Ig Nobel and the long joke
Parnell and Mainstone eventually received one of science’s more unusual honours. In 2005 they were awarded the Ig Nobel Prize in Physics for patiently conducting the experiment that had begun in 1927.
The Ig Nobels celebrate achievements that first make people laugh and then make them think. An experiment that drops roughly once a decade, watched by generations of physicists who repeatedly miss the decisive instant, fits that description unusually well.
Mainstone accepted the prize in person. Parnell, who had died more than half a century earlier, received it posthumously.
What happens when the drop falls
For years, pitch from the funnel creeps downward under gravity. A bulb gradually develops beneath the stem and lengthens so slowly that the change is far easier to see in images taken months apart than from standing beside the display.
Eventually the connection between the hanging drop and the pitch above becomes narrow enough for separation to occur. The final movement is brief compared with the years spent forming the drop.
The clean beaker now beneath the funnel also means the tenth drop has more room than its predecessor. The ninth had descended into the old pile before the beaker was changed; the new arrangement was intended to give subsequent drops space to fall.
That contrast is part of what makes the next event interesting. The waiting takes years. The part everyone wants to witness is over almost immediately.
The next drop
As of this writing, the tenth drop is still forming. Its current cycle began after the old beaker was removed in April 2014, leaving the experiment with a fresh space beneath the funnel.
Predicting an exact date is difficult because the apparatus is not maintained under precisely controlled environmental conditions and the pitch’s flow is strongly temperature-dependent. Previous intervals therefore offer guidance, not a timetable.
UQ continues to say only that the tenth drop is expected sometime in the 2020s. It could arrive sooner than another simple decade-by-decade extrapolation suggests, or it could keep the watchers waiting.
The material Thomas Parnell poured into a funnel in 1927 is still moving almost a century later. A camera is watching, a clean beaker is waiting underneath, and the vigil goes on.
