It was an adjustable in height mirror that could be balanced at any position, simultaneously producing musical notes. The mirror could be raised or pulled down without particular force. It was invented by Ktesibios in the 3rd century B.C. (for his father’s barber shop).
The balancing mechanism of the mirror consisted of a lead balancing weight (positioned behind the mirror), two pulleys (above the mirror and the weight respectively) and a rope, which connected the mirror to the weight, running through the pulleys. The balancing weight ensured the rising force of the mirror while the friction of the pulleys ensured its balance.
The sound producing mechanism consisted of a closed vertical tube, inside which the balance weight slid, and a few musical pipes (“auloi”) incorporated at its base. The motion of the weight pressed the trapped air towards the “auloi” which produced the desired musical notes.