Tar drop 70 years in the making

Scientists who waited almost 70 years to see a drop of tar fall have put the term "like watching paint dry" to shame.

The Dublin pitch-drop experiment, one of the longest-running laboratory investigations in the world, captured a drop of tar falling on camera for the first time, the Huffington Post reported.

The experiment was set up in 1944 at Trinity College in Dublin to show the high viscosity of pitch – also known as bitumen.

Bitumen appeared solid at room temperature, but it was actually flowing extremely slowly.

Physicists set up a webcam in April so anyone could watch and try to be the first person ever to witness the drop fall.

About 5am Dublin time on July 11, physicist Shane Bergin and his colleagues captured footage of the event.

"We were all so excited," Bergin said.

"It's been such a great talking point with colleagues eager to investigate the mechanics of the break, and the viscosity of the pitch."

The Trinity College team estimated the viscosity of the tar, and put it at about 2 million times more viscous than honey, or 20 billion times the viscosity of water, the Huffington Post said.

The Atlantic said if you hammered tar, it would shatter like glass.

The Dublin study was started after a similar Australian one, which was the world's longest-running laboratory experiment, according to the Guinness World Records.

Physicist Thomas Parnell set it up to show everyday materials could have surprising properties.