Professor Thomas Parnell, of the University of Queensland in Brisbane, wished to show his students that pitch, the paving tar often used on roofs and roads, was a fluid not only on very hot days or just after being poured, but all the time. By doing so, he started one of the longest running experiments in history.
Pitch is a fluid, but we don't often see it move. It has a high viscosity; a high resistance to movement. It's only when the temperature gets high that it flows easily. Parnell started his demonstration in 1927 by melting down some pitch, making sure it was evenly mixed, and then pouring it into a funnel. The funnel was sealed at the bottom, to prevent the pitch from flowing right through. It wasn't until 1930 that the seal was removed. Parnell wanted to be sure that the pitch was completely cooled before the experiment could be started.
The tip of the funnel was opened and students waited for the first drip. They then graduated, and a new batch of students waited for the drip. They graduated, and the next batch of students saw the first drip of pitch, which came in 1938. The next one came in 1947. The next in 1954. Drips came about once every decade, except the seventies when two drops fell, one in 1970 and once in 1979 (it was a rockin' time). The nineties, on the other hand, were dropless. The overall rate of the drips has slowed down. The last one was in 2000, and the next drip is expected in 2012. The slow-down could be because of less pressure from above, or it could be because the climate and temperature of the experiment is being controlled more now than it was in the first half of the twentieth century.
A webcam is recording this drop-to-be, and can be found here. (Windows Media Format)