Padre Giambattista Embriaco, Roma.

The patinated metal case depicts a traditional Italian water fountain and is decorated with mythical nautical figures, geese, and shells. To the front is the water reservoir and at the top sits the dial assembly. The whole stands on a carved architectural base with gilt-bronze mounts, a marble top and an inner compartment that houses the second water reservoir.

The white porcelain dial has black Roman numerals for the hours, a gilt-bronze beaded bezel, an oak leaf garland with the three points of a trident at the center and is signed ‘idrocronometro, P. Embriaco, Roma’.

Unlike most other clocks the power is derived by flowing water. The small pump in the interior water reservoir pumps the water up to the outlet that is framed by a mythical figure. As the water falls it is captured by alternating sides of a 2 chambered pivoted reservoir adorned with shells. Carried on the back of the center arbor is a cross piece that has steel pin pallets that are released by the two finely threaded adjustable knurled screws at the ends of the long brass springs. Also connected is a thread that runs to a counterbalanced arm with multiple springs that advances one of the wheels by one tooth every other swing of the pendulum. The compound pendulum is suspended by a spring suspension, has adjustable lenticular bobs top and bottom and a pivoted bar in the center that pushes the springs.

As the chamber in front fills the pendulum swings and pushes the spring away from the pin pallet allowing the heavier chamber to fall. Every other ‘beat’ the bar in back imparts, through the thread, an impulse to the under dial gearing thus advancing the hands.

There are very few even partial examples extant, and this is one of the only complete and functioning ones. Originally the clock would have been hooked up to a water supply eliminating the need for the second reservoir and pump but has now been adapted to a closed system.

For additional information see:

https://en.wikipedia.org/wiki/Hydrochronometer

Water-Driven Clocks by Allan A. Mills on page 136 of the summer addition of Antiquarian Horology.