Final answer:
The hydraulis is an ancient Greek instrument that is a predecessor to the modern pipe organ, which uses air pressure regulated by bellows or electric blowers instead of water.
Step-by-step explanation:
The hydraulis is considered to be a predecessor to the modern-day pipe organ. This ancient Greek instrument, invented in the 3rd century BC, used water to regulate the air pressure to the organ pipes, hence the name hydraulis, meaning water (hydro-) pipe (-aulis).
Over time, the mechanism evolved, and by the time of the Baroque period, the organ became a complex instrument capable of a wide range of sounds and dynamic levels, moving away from the use of water pressure to bellows and eventually to electric blowers in modern organs. The musical principles established by the hydraulis, however, laid the foundation for the development of keyboard instruments, including the pipe organ.