Inside a glass bell jar at the University of Queensland in Brisbane, a black mass of pitch has been moving almost imperceptibly through a funnel since its sealed stem was cut in 1930. Thomas Parnell created the experiment in 1927, and nine drops have been recorded since then. No person has witnessed the moment one of the Queensland drops fell freely from the funnel.
Parnell, UQ’s first professor of physics, wanted to demonstrate that a material hard enough to shatter under a hammer at room temperature could still flow. He heated a sample of pitch, poured it into a glass funnel with a sealed stem, and allowed it to settle for three years. In 1930, he opened the stem and let gravity begin its work.
Parnell died in 1948. By then, the first two drops had reached the beaker, but he had not seen either one fall.
What is actually in the jar
The apparatus is humble. A glass funnel sits clamped above a beaker, with the arrangement enclosed beneath a bell jar. The black pitch hangs from the funnel in a long tendril that appears frozen when viewed over minutes or hours.
A 1984 analysis published in the European Journal of Physics estimated the pitch’s viscosity at approximately 2.3 × 108 pascal-seconds, or about 230 billion times the viscosity of water at 20°C. The calculation carried substantial uncertainty because the funnel could not be measured precisely without risking damage to the experiment.
Pitch behaves as an extremely viscous fluid over long periods, even though it feels solid and can fracture when struck suddenly. A drop gradually forms, lengthens, and eventually separates from the material above. Temperature matters too. Early drops arrived roughly seven to nine years apart, while later drops took longer after changes to the building’s temperature conditions.
The chronicle of missed appointments
The recorded dates stretch across generations. The first drop fell in December 1938, eight years after the stem was opened. The next drops were recorded in 1947, 1954, 1962, 1970, 1979, 1988, 2000, and 2014.
John Mainstone became the experiment’s second custodian in 1961 and looked after it for 52 years. In 1988, he stepped away for five minutes while the experiment was being displayed at Brisbane’s World Expo. In 2000, a 20-minute power outage prevented the monitoring camera from recording the eighth drop’s crucial moment.
Mainstone and Parnell were jointly awarded the 2005 Ig Nobel Prize in physics, with Parnell receiving the honour posthumously. Mainstone continued tending the experiment until his death in August 2013.
The one that fell in Dublin
A separate pitch-drop demonstration was established at Trinity College Dublin in October 1944 by someone whose identity is no longer known. On 11 July 2013, physicists Shane Bergin and Stefan Hutzler captured a drop detaching and falling on camera. Trinity describes it as the first successful recording of such an event.
The footage shows a slow separation followed by a sudden fall into the container below. Mainstone saw and repeatedly examined the Dublin recording before his death about six weeks later.
Queensland’s ninth drop behaved differently. In April 2014, it made contact with the eighth drop instead of breaking free. Researchers inferred the date of contact from changes in its rate of descent because the meeting point was obscured from the cameras.
On 24 April, custodian Andrew White attempted to replace the beaker. The apparatus briefly lifted when the degraded seal beneath the bell jar resisted, and the resulting movement separated the ninth drop’s stem from the funnel. It is counted as the ninth drop, but it was not an ordinary, freely falling event captured by a webcam.
Why the falls are so easily missed
A drop develops over approximately a decade, while its final separation can happen in moments. For any one observer, the chance of looking at the funnel at precisely the right time is tiny. The eighth drop also showed that continuous monitoring equipment can fail at exactly the wrong moment.
The ninth drop presented a different problem. Because it touched the older pitch below rather than falling freely, there was no sudden motion for a person to notice. Even several cameras could not reveal an exact instant of contact without later analysis.
Human attention is tuned to changes unfolding over seconds and minutes. The Queensland experiment operates on a scale of years and decades.
What the experiment is really for
Guinness World Records recognises the apparatus as the longest-running laboratory experiment. It began as a lecture demonstration, but it has also produced a published viscosity estimate and a dated record of the pitch’s irregular flow.
Its scientific output is sparse rather than nonexistent. The 1984 paper used the accumulated pitch, the funnel’s dimensions, and the elapsed time to calculate viscosity. It also explained why the result carried considerable uncertainty, including seasonal temperature changes and the difficulty of measuring the historic apparatus accurately.
The pitch drop can be compared with Oxford’s Clarendon Dry Pile, commonly called the Oxford Electric Bell, which was set up in 1840 and has rung billions of times. The Queensland funnel works differently, producing a new physical event only once every several years.
The experiment predates the discovery of nuclear fission, the transistor, the first human landing on the Moon, and the World Wide Web. It has also outlasted the careers of nearly everyone entrusted with watching it.
The tenth drop
The tenth drop has been forming since 2014. UQ maintains a live stream, and published estimates continue to place its possible fall sometime in the 2020s, although no exact year can be predicted.
Anyone with an internet connection can watch the funnel through UQ’s stream. Whether someone finally witnesses the next separation live will depend on the drop’s behaviour, the cameras, and another small contest between patience and timing.
When the tenth drop separates, the record will be updated and the next cycle will begin. The timing of the eleventh drop will remain uncertain for years.
The pitch does not respond to the attention surrounding it. It simply continues flowing at a pace that has already carried one classroom demonstration through almost a century of scientific history.