What I’m about to describe is supposedly the world’s longest-running scientific experiment, and, although we already know the result, it gets demonstrated repeatedly: once every decade on average.
In 1927, Professor Thomas Parnell of the University of Queensland set up an experiment to demonstrate that some substances that appear to be solid, like pitch, are really liquids, and flow at an extremely slow rate. At room temperature, for example, pitch is solid, brittle, and can be shattered with a hammer. But Parnell wanted to show that it was really a liquid in the technical sense.
So, in 1927 Parnell heated up some pitch, poured it into a sealed funnel, allowed it to congeal for three years, and then snipped the neck of the funnel. Over the next 86 years (Parnell died 21 years into the experiment), generations watched the pitch slowly drip from the funnel (nobody’s actually seen a drop fall).
Here’s a photo of the setup:
Up until last week, there had been eight drops, but a ninth just fell on April 10. Here’s a time-lapse video taken over the last two years:
Sadly, the fall isn’t so dramatic, as the latest drop simply glopped onto the one below it, still adhering to the funnel. They need to move that funnel higher up!
There’s another description of the experiment at the University of Queenland’s site, which gives a bit more information:
The experiment was set up as a demonstration and is not kept under special environmental conditions (it is actually kept in a display cabinet in the foyer of the Department), so the rate of flow of the pitch varies with seasonal changes in temperature. Nonetheless, it is possible to make an estimate of the viscosity of this sample of pitch (R.Edgeworth, B.J. Dalton and T. Parnell, Eur. J. Phys (1984) 198-200). It turns out to be about 100 billion times more viscous than water! The first picture in the slide show above is of the late Professor John Mainstone, longtime custodian of the experiment. In the 83 years that the pitch has been dripping, no-one has ever seen the drop fall.
The history (from Wikipedia):
By the way, I’m told that very old windows are thicker at the bottom than at the top, supposedly the result of glass itself flowing downward. I have no idea whether this is true.