379
Chap. 2.] Porta's Natural Magic.
specimens from which others for practical purposes might be deduced.1t is quite a common remark in old authors, after describing a device, toobserve that various machines for othor purposes may be derived from it,and excuse themselves for not pointing out particular modes of doing this,because they considered them too obvious to require it.
Whether such modes of raising water were practised in Europe previ-ous to the sixteenth Century, we have no means of aicertaining; butin themiddle of that and the beginning of the following one they are frequentlyto be met with in old authors.
Baptist Porta, m his Natural Magic, after describing a method of rais-ing water from the bottom to the top of a tower, by means of a vacuumformed by water flowing from a close vessel;—next proposes a mode ofaccomplishing the same object “ by heat alone.” A close vessel of brasswas to be placed upon the tower, having a pipe connected to its upperpart and extending down to the water to be raised ; the orifice being ashort distance below the surface. The vessel was then “ to be madehot by the sun, or fire,” to rarefy the contained air and expel a portion of itthrough the pipe. As the vessel grows cold, he observes, the remainingair is Condensed, and because it cannot then fill the vacuity, “ the water iscalled in and ascends thither.”* (Book xix . chap. 3.) He does not men-tion the height of the tower because the philosophers of that age had noidea that the elevation to which water would ascend into a vacuum hadany limits—and hence in another part of the same Work Porta uses thefollowing language—“ A vacuum is so abhorred by nature that the Worldwould sooner be pulled asunder than any vacuity can be admitted.”(Book xviii. chap. 1.) There is another passage in the 5th chapter of the19th Book , from which it seems that he employed the elastice force ofair or steam, or a mixture of both as in No. 174—and generated either bythe heat of the sun, or by that of lamps or candles, as shown at No. 189.
After describing a fountain of compression, which he exhibited to someof the great Lords of Venice , and the Operation of which he says causedgreat surprise as there was no visible cause for the Water flying so high—he continues, “ I also made another place near this fountain that let in light,and when the air was extenuated, so long as any light lasted the fountainthrew out water, which was a thing of much admiration, and yet but littlelabor.” This passage is probably imperfectly translated.
No. 174, on the next page, forms the 9th plate attached to the “ ForcibleMovements” of Decaus. (Translated by Leak, London , 1659.) Itexhi-bits an extension of Heron’s machine already noticed, (No. 173.) Decaussays “ this engine hath a great effect in hot places as in Spain and Italy .”
Pour air tight copper vessels, a foot square and 8 or 9 inches deep, areso arranged that the sun may shine strongly upon them. A pipe, havinga valve o, opening upwards, communicates with the lower part of each, tosupply them with water from the spring below. Another pipe passesover the upper surfaces, having branches which descend nearly to the bot-tom of each vessel. A valve is also placed in this pipe, from the upperend of which the jet of the fountain issues. At the commencement, eachvessel is about one third filled with water, through openings on the top,which are then plugged up. “ Then the sun shining upon the said en-gine shall make an expression by rarefying the enclosed air and force the
a Natural Magick in tmenty baoks by John Baptist Porta, irjierein are setforthall the richesand delights of the Natural Sciences .”— London , 1658.
Itcontains, beside a multitude of absurdities, many ingenious deviccs. The trombe,camera obscura, air gun, repeating guns, air tubes, ear trumpets, &c. &c. are described.The work was first published in 1560.