Professor John Mainstone, the longtime custodian of the University of Queensland’s famous Pitch Drop experiment, has died after suffering a stroke.

For more than 50 years, Professor Mainstone monitored dripping tar from a glass funnel sitting in the lobby of the university’s physics department.

The experiment began in 1930 as a way for the late Professor Thomas Parnell to prove the liquid nature of a solid object at room temperature.

Having formed just nine drops in 81 years, it is recognised by the Guinness Book of World Records as the longest running experiment in the world.