Philo of Byzantium Describes the Earliest Escapement Mechanism

The earliest liquid-driven escapement was described by the Greek engineer and writer on mechanics Philo of Byzantium (Φίλων ὁ Βυζάντιος) in his technical treatise Pneumatica (πνευματικά; Pneumatics) chapter 31 as part of a washstand. Philo's Pneumatica was part of a larger work, Mechanike syntaxis (Compendium of Mechanics).

Philo's device worked as follows: a counterweighted spoon, supplied by a water tank, tipped over in a basin when full, releasing a spherical piece of pumice in the process. Once the spoon emptied, it was pulled up again by the counterweight, closing the door on the pumice by the tightening string. Philo's comment that "its construction is similar to that of clocks" indicates that such escapement mechanisms were already integrated in ancient water clocks.