Fig. 1.—Opening Temple-Doors by Steam, b. c. 200.
Hero sketches and describes a method of opening temple-doors by the action of fire on an altar, which is an ingenious device, and contains all the elements of the machine of the Marquis of Worcester, which is generally considered the first real steam-engine, with the single and vital defect that the expanding fluid is air instead of steam. The [sketch], from Greenwood’s translation, exhibits the device very plainly. Beneath the temple-doors, in the space A B C D, is placed a spherical vessel, H, containing water. A pipe, F G, connects the upper part of this sphere with the hollow and air-tight shell of the altar above, D E. Another pipe, K L M, leads from the bottom of the vessel, H, over, in syphon-shape, to the bottom of a suspended bucket, N X. The suspending cord is carried over a pulley and led around two vertical barrels, O P, turning on pivots at their feet, and carrying the doors above. Ropes led over a pulley, R, sustain a counterbalance, W.
On building a fire on the altar, the heated air within expands, passes through the pipe, F G, and drives the water contained in the vessel, H, through the syphon, K L M, into the bucket, N X. The weight of the bucket, which then descends, turns the barrels, O P, raises the counterbalance, and opens the doors of the temple. On extinguishing the fire, the air is condensed, the water returns through the syphon from the bucket to the sphere, the counterbalance falls, and the doors are closed.
Another contrivance is next described, in which the bucket is replaced by an air-tight bag, which, expanding as the heated air enters it, contracts vertically and actuates the mechanism, which in other respects is similar to that just described.
In these devices the spherical vessel is a perfect anticipation of the vessels used many centuries later by several so-called inventors of the steam-engine.
Proposition 45 describes the familiar experiment of a ball supported aloft by a jet of fluid. In this example steam is generated in a close cauldron, and issues from a pipe inserted in the top, the ball dancing on the issuing jet.
