Hydraulis

Well kiddo, a hydraulis is a really cool musical instrument that was invented way back in Ancient Greece. It was kind of like an organ, but instead of using air to make sounds, it used water!

Here's how it worked: The hydraulis had a big tank of water called a reservoir. There were pipes that went from the reservoir to "keys" that you could press down to make different notes. When you pressed down on a key, it opened up a little valve that let water flow through the pipe. The water would hit a "water organ pipe," which was like a whistle or a flute, and make a sound.

But it wasn't just the water that made the sound - there was also air involved. Inside the water organ pipe there was a little piston that moved back and forth, kind of like your lungs when you breathe. This movement made the air vibrate, which created the sound you heard.

Back then, people used the hydraulis to play music during religious ceremonies and at theaters and sporting events. It was really popular because it was loud and it could make lots of different sounds. Plus, it was pretty magical to watch all that water moving around and making such beautiful music!