According to Pliny, the doors of the labyrinth of Thebes were constructed in such a manner that when they were opened a sound resembling that of thunder greeted the astonished worshipers.
Heron, in his Pneumatics, describes an apparatus for blowing a trumpet on opening the door of a temple, the effect of which must have been awe inspiring to the uninitiated common people.
It is hardly necessary to give a detailed translation of the text of the Greek engineer, as the modus operandi of the experiment is sufficiently explained by reference to the descriptive {6} picture. It will suffice to add: One sees that when the door of the temple is opened, a system of cords, rods and pulleys causes a hemispherical cap, to the upper part of which the trumpet is attached, to sink into a vase full of water. The air compressed by the water escapes through the instrument, causing it to sound.
MECHANISM WHICH CAUSED THE TEMPLE DOORS TO OPEN WHEN A FIRE WAS LIGHTED ON THE ALTAR.
Another remarkable device is described in the Pneumatics of Heron, and consists of an apparatus which is entitled: “Construction of a chapel wherein, when fire is lighted upon the altar, the doors open, and when it is extinguished, they close.” {7}
The altar is hollow, and when a fire is lighted thereon, the air contained in the interior expands and begins to press upon the water with which the globe situated beneath is filled. The water then rises through a bent tube which leads to a species of pot, into which it falls. The pot is suspended upon a cord which passes along a pulley, doubling immediately, in order to enroll itself about two cylinders, which turn upon pivots, said cylinders forming the prolongation of the axes upon which the doors above turn. Around the same cylinders are enrolled in a contrary manner, two other cords, which also unite into one before passing along a pulley, and then hanging vertically for the support of a counterpoise.
EGYPTIAN ALTAR
It is clear that when the water from the globe enters the pot, the weight of the latter will be augmented and it will sink, pulling upon the cord which has been wound about the cylinders {8} in such a way as to cause the doors to open, when it is drawn in this direction.