A hydrochronometer is a type of water clock. There are actually two of these extremely rare clocks located in Rome, the other is at Palazzo Berardi.
Father Giovan Battista Embriaco was an inventor and professor at the College of St Thomas. Embriaco created this hydrochronometer in 1867, and after its completion, it was sent to the Paris Universal Exposition where it received several awards.
The clock returned to Rome in 1873 and was placed on the Terrazza del Pincio in the Villa Borghese gardens. It was installed as part of a fountain designed by architect Gioacchino Ersoch.
The fountain is still at the site, although it had a brief period away from the Villa Borghese gardens. It was returned in 2007 after two years of restoration works. The water clock uses the force of water to move the pendulum and wind the clock.
Know Before You Go
The rest of the Terrazza is also worth a visit, it provides especially stunning views over Piazza del Popolo below.