The longest running experiment in the world has finally reached another milestone after 83 long years. The "Pitch-drop experiment" involving watching drops of pitch form and fall has revealed even more information about the flow of pitch.

The experiment was first started back in 1927 by a physicist from the University of Queensland in Brisbane named Thomas Parnell. The aim of the experiment was to measure the flow of pitch over a long period of time. Pitch is one of the most viscous liquids in the world. While the substance appears solid at first glance, the material actually flows very slowly. In fact, forming a drop from a blob of pitch can take a few years. Asphalt, also sometimes referred to as bitumen, is the most commonly known type of pitch.

For most of the duration of the experiment, the blob of pitch was watched over by John Mainstone, a physicist from Queensland University. Unfortunately, Mainstone missed all of the three drops that occurred during the time he watched over the experiment. The experiment was concluded 8 months after Mainstone passed away. All in all, Mainstone spent more than 50 years supervising the blob of pitch.

The last observed drop happened over 13 years ago. With the latest drop however, researchers have documented a total of 9 drops that occurred over the course of the experiment.

"Two things changed after that - the 2000 (eighth) and 2014 (ninth) drop each took about 13 years to fall, and each collided into the decades-old pile of drops in the beaker before it could break away from the funnel," said Andrew White, a professor from the University of Queensland. "It was still connected to the ninth drop but almost broke free this year." White is also the current custodian of the experiment.

The researchers say that the drops fell at average rate of one drop for every 8 years that passed. Back in the year 2000, the researchers documented that the 8^th drop of pitch came in contact with the 7^th drop. However, it still took around 14 years for the drop to fall. Earlier this year, the 8^th drop was still in contact with the 9^th drop and observers noted that there was a time when the 8^th and 9^th drops almost separated.

"The connection had become thin, stressed and light grey - but now that the ninth drop has run into it the whole cycle starts again," Professor White said. "To determine the actual moment, we're going to analyse the video to see if and when the pitch motion slowed down, and hopefully we can let people know soon."

Due to the extremely slow nature of the experiment, observing the exact moment when the drops fell was difficult. In the year 2000, researchers tried pointing a webcam at the experiment. When the 8^th drop fell however, a 20 minute power outage occurred that prevented the webcam from capturing the moment on video. After the failed attempt, the researchers then increased their surveillance of the blob using three webcams to make sure the next event was captured on video. The ninth drop can be observed at www.theninthwatch.com.