Porta is described as a mathematician, chemist, and physicist, a gentleman of fortune, and an enthusiastic student of science. His home in Naples was a rendezvous for students, artists, and men of science distinguished in every branch. He invented the magic lantern and the camera obscura, and described it in his commentary on the "Pneumatica." In his work,[12] he described this machine for raising water, as shown in Fig. 4, which differs from one shown by Hero in the use of steam pressure, instead of the pressure of heated air, for expelling the liquid.
[12] "Pneumaticorum libri tres," etc., 4to. Naples, 1601. "I Tre Libri de' Spiritali." Napoli, 1606.
The retort, or boiler, is fitted to a tank from which the bent pipe leads into the external air. A fire being kindled under the retort, the steam generated rises to the upper part of the tank, and its pressure on the surface of the water drives it out through the pipe, and it is then led to any desired height. This was called by Porta an improved "Hero's Fountain," and was named his "Steam Fountain." He described with perfect accuracy the action of condensation in producing a vacuum, and sketched an apparatus in which the vacuum thus secured was filled by water forced in by the pressure of the external atmosphere. His contrivances were not apparently ever applied to any practically useful purpose. We have not yet passed out of the age of speculation, and are just approaching the period of application. Porta is, nevertheless, entitled to credit as having proposed an essential change in this succession, which begins with Hero, and which did not end with Watt.
[Illustration: FIG. 4.--Porta's Apparatus, A. D. 1601.]
The use of steam in Hero's fountain was as necessary a step as, although less striking than, any of the subsequent modifications of the machine. In Porta's contrivance, too, we should note particularly the separation of the boiler from the "forcing vessel"--a plan often claimed as original with later inventors, and as constituting a fair ground for special distinction.
The rude engraving (Fig. 4) above is copied from the book of Porta, and shows plainly the boiler mounted above a furnace, from the door of which the flame is seen issuing, and above is the tank containing water. The opening in the top is closed by the plug, as shown, and the steam issuing from the boiler into the tank near the top, the water is driven out through the pipe at the left, leading up from the bottom of the tank.