The professor who spent a half-century overseeing the world’s longest-running lab study, the Pitch Drop Experiment, has died of a stroke without ever observing the effect it was designed to measure.

John Mainstone, 78, died last week, the University of Queensland in Australia announced Monday. For 52 years, he was custodian of the world-famous experiment, in which a seemingly-solid piece of tar dripped through a glass funnel, proving that it acts like a liquid over time.

The tar has only dropped eight times since the experiment began in 1927, most recently in 2000, and has never been observed. Scientists are eager to study the physics involved at the precise moment the tar drops.

“John’s death is particularly sad as in his time as the custodian of the experiment, he did not see a single drop fall,” said Professor Halina Rubinsztein-Dunlop, head of the university’s School of Mathematics and Physics.

“Professor Mainstone’s dedication to the long-running experiment well past his official retirement ensured that media, researchers and undergraduate students had easy access to relevant information and an understanding of the important science behind it,” she said.

Mainstone began observing the Pitch Drop Experiment in January of 1961, and barely missed the rare event three times.

In April of 1979, Mainstone saw that the rare event appeared to be close, checked it on a Saturday, and found it had fallen by early Monday morning, the professor said in an interview which aired on NPR’s Radiolab program.

Almost a decade later, in 1988, Mainstone again missed the pitch drop when he briefly left his post.

“I decided that I needed a cup of tea or something like that, walked away, came back, and lo and behold it had dropped,” Mainstone said in the interview. “One becomes a bit philosophical about this, and I just said, ‘Oh well, let’s be patient.'”

Not taking any chances, a camera was then installed that would record the exact moment the next drop fell, as it did in 2000 — but the system malfunctioned.

There are now three webcams recording the experiment, and people around the world can watch and wait for the next drop to fall. You can view the live cam here.

The pitch took three years to settle. The experiment has been running for 83 years since the material, 100 billion times more viscous than water, began flowing.