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. No. 47 is a device subsequently reproduced--perhaps reinvented by the second Marquis of Worcester. [Illustration: FIG. 2.--Steam Fountain, B. C. 200.] A strong, close vessel, _A B C D_, forms a pedestal, on which are mounted a spherical vessel, _E F_, and a basin. A pipe, _H K_, is led from the bottom of the larger vessel into the upper part of the sphere, and another pipe from the lower part of the latter, in the form of a syphon, over to the basin, _M_. A drain-pipe, _N O_, leads from the basin to the reservoir, _A D_. The whole contrivance is called "A fountain which is made to flow by the action of the sun's rays." It is operated thus: The vessel, _E F_, being filled nearly to the top with water, or other liquid, and exposed to the action of the sun's rays, the air above the water expands, and drives the liquid over, through the syphon, _G_, into the basin, _M_, and it will fall into the pedestal, _A B C D_. Hero goes on to state that, on the removal of the sun's rays, the air in the sphere will contract, and that the water will be returned to the sphere from the pedestal. This can, evidently, only occur when the pipe _G_ is closed previous to the commencement of this cooling. No such cock is mentioned, and it is not unlikely that the device only existed on paper.