The doors close themselves in the following manner: The bent tube, which places in com­mu­ni­ca­tion the globe and the pot, forms a siphon, the longest branch of which plunges into the globe. When the fire is extinguished upon the altar, the air contained in the latter and in the globe, cools, and diminishes in volume. The water in the pot is then drawn into the globe, and the siphon, being thus naturally influenced, operates until the water in the pot has passed over into the globe. In measure as the pot lightens, it remounts under the constraint of the counterpoise, and the latter, in its descent, closes the doors through the intermedium of the cords wound around the cylinders.

HOW THE STATUES WERE MADE TO POUR LIBATIONS WHEN A FIRE WAS KINDLED ON THE ALTAR.

Heron says that mercury was sometimes used in place of water, by reason of its superior weight. {9}

Certain altars were provided with such mechanism as to afford to the faithful even more astonishing spectacles. Here is another experiment from the learned Heron:

“To construct an altar so that when one kindles the fire thereon, the statues which are at the sides shall pour out libations.”

There should be a pedestal, upon which are placed the statues, and an altar closed on all sides. The pedestal should communicate with the altar through a central tube, also with the statues by means of tubes, the ends of the latter terminating in cups held by the statues. Water is poured into the pedestal through a hole, which is stopped up immediately afterward.

If, then, a fire be kindled upon the altar, the air within expanding, will penetrate the pedestal and force out the water; but the latter, having no other outlet than the tubes, mounts into the cups and the statues thus perform libations, which last as long as the fire does. Upon the fire being extinguished, the libations cease, and recommence as many times as it is rekindled.

The tube through which the heat is conveyed should be larger at the middle than at the extremities, to allow the heat, or more especially, the draft, which it produces, to accumulate in an inflation, in order to be most effectual.

The priests of the temples of old were truly masters of the arts of mechanics and pneumatics.