Researchers with UC Davis’ Tahoe Environmental Research Center have been tracking water clarity for more than 50 years. But the method for taking those measurements can be traced back to the 1800s in Vatican City. Advertisement It was then that Papal scientist Father Angelo Secchi developed the Secchi Disk: a small weighted plate that is used to gauge visibility as it’s lowered deep into open water. “Angelo Secchi was possibly the greatest scientist nobody’s ever heard of,” Brother Guy Consolmagno, the current director of the Vatican Observatory, said. UC Davis TERC staff still use the Secchi Disk every 10 days, monitoring changes in Lake Tahoe year-round.