Ancient Greece: Herons Trumpet Signal

Heron or Hero of Alexandria was an ancient Greek mathematician and engineer who resided in the Egyptian Roman province doing his life between 10-70 AD. He is widely known to be the greatest experimenter from antiquity. He likey also helped teach at Musaeum which formerly had included the well-known Biblioteca de Alexandria or (Library of Alexandria). Although he has multiple more well-known inventions such as the first vending machine, windwheel, simple steam engine, and cuckoo clock. One of Hero's lesser-known yet no less brilliant inventions was the Herons Trumpet Signal.

What is Herons Trumpet?

For the use in temples, Herons Trumpet Signal created a sound when a temple door was opened. The sound of a trumpet was triggered by the opening of the temple doors. Heron proposes following construction in his 'Pneumatic':  A rope is mounted on the door of the temple, which pulls a lever. This lever pushes a hemisphere into a water jar. The water presses air into the hemisphere. This air will now float through a trumpet, which is mounted on the hemisphere. A tone is created by pressure. If the door is closed, the lever falls back to its first position. The hemisphere lifts and air will float into it.

The animation below shows what the process would look like in action. 

Herons Trumpet Signal Design

The design is the following. Behind the entrance, there will be a vessel, (labeled A B C D) that contains water. In this reversal, a narrow-necked vessel, shaped like an extinguisher, F, with which, at its lower extremity, this same trumpet, H K, responds, provided with a bell and a mouthpiece. Simultaneously with the tube of the trumpet, and attached to it, let the rod L M run, fastened, at the lower end, to the vessel F, and having at the other extremity al loop, M: let the beam N X pass through this loop, thus supporting the vessel F, at a sufficient height above the water. A pivot 0 must be turned on by the beam N X, the end X must be fastened to the back part of the door with the pulley P. When the door is opened, the cord is extended, and the beam X is drawn up so that the beam N X does not support the loop M anymore, and when the loop is changed in consequence the vessel F descends into the water and gives a trumpet sound through the ejection of air via the mouthpiece and bell.

Heros Lasting Impact 

Sadly many of Heron's original writings and invention designs were lost after being burned sometime between the late 4th and 5th centuries. In fact, most of his original writings and designs have been lost. However, some of his works were preserved by Arabic manuscripts. Luckily what remained of Hero's work still is able to provide a fascinating insight into the technological advancements of ancient Greek-Roman civilization. You could even say he was the father of cybernetics. His work was the first formal cybernetics work that was ever carried out. Especially his "programmable" automation devices.