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PORTA. The attention which was given to the “ Pneumatica” by Italian authors, and among others by Porta, can hardly be accounted for from the gratification of that pedantry, which has been called the besetting sin of the age. Five translations, and other reprints, in so brief a space of time, must have been produced, even among scholars, by something besides a mere admiration of its classical origin.

In the warm climate of Italy, one of the most luxurious accompaniments of a shady grove, a magnificent colonnade, or piazza, is a fountain, or jet of water. Besides the delightful freshness it produces, by giving a motion to the “listless air,” the variety of agreeable contrasts water forms with the productions of the statuary and architect, made jets and fountains ornaments which all were ambitious of possessing. To raise water, therefore, in abundance, and to distribute it with judgment and skill, were subjects of such general importance, that any thing teaching the best modes of accomplishing either, could not fail of exciting considerable attention. The “ Pneumatica," according to Muratori, which taught a variety of elegant whims, in which water, by simple means, was made to form effects which were so much admired and coveted, received only that attention which was, its due, as an admirable practical

“E vi accorgerete della quantità dell'acqua uscita, che l' acqua si e risoluta in tant aria.

“Si può ancora agevolmente misurare un'oncia di aria nella sua consistenza in quante parti di aria più sottile si può dissolvere.” I Tri Libri Spiritali, p. 76. "Napoli, 1606.

In another experiment a vacuum is formed by condensation, and water is forced'upwards into it by the pressure of the atmosphere: and this is the basis of an ingenious mode of estimating the space into which the air or vapour has expanded. p. 76. Ibid.

DECAUS.

27 book; and which, on this account, it would have commanded, had it been first written, instead of being translated by Aleotti. One thing is obvious, that, after his excellent translation, a wonderful variety and elegance of illustration were introduced into hydraulic and pneumatic disquisitions.

The imitation of the style of Italian buildings, also, introduced into other countries the use of ornamental fountains; and Solomon Decaus, a French engineer and architect, was among the first who, following the prevailing taste, gave designs for their construction.

Of Decaus's history nothing is known; but it may be collected from a book he published at Frankfort in 1615, that he was known to, and had been in the service of, Charles I, when Prince of Wales ; that he had designed some hydraulic ornaments for that prince's palace at Richmond, and others to satisfy his royal highness's

gentille curiosité.Some of these, he says, are described in his “ Raisons des Forces Mouvantes," the second part of which he dedicates to Charles's sister, Elizabeth, Electress Palatine. In 1615 he was residing at Heidelberg, from which place he dates his dedications to the king of France, and to the Princess.*

* Les Raisons des Forces Mouvantes, avec diverses machines tant utile que plaisantes, auxquelles sont adjoints plusieurs desseins de grotes et fontaines, augmentées de plusieurs figures, par Salomon de Caus, Ingénieur et Architecte du Roy. Frankfort, 1615. Another edition, in which the Epitre Dedicatoire is dated Heidelberg, 15th February, 1615, and the permission to print is dated 1614, but it is printed for C. Sevestre, Paris, 1624. A third, with an altered title, “ Nouvelle invention de lever l'eau haut que sa source, avec quelques machines mouvantes, par le moyen de l'eau, et un discours de la conduite d'Icelle, avec beaucoup de figures, par Isaac de Caus, Ingénieur et Architecte à Charles le Premier, Roy de

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In copying the contrivances in the“ Spiritalia," as hydraulic and pneumatic machines, Decaus and his contemporaries did not yield either in ingenuity, or love of the marvellous, to any of their Italian precursors; but among much irrelevant speculation and impracticable combination, we begin to observe a leaning to experiment; yet it may be questioned, whether the partial essays, which were coming into vogue, did not, in many cases, produce a greater deviation from sober truth, than the pure speculation which preceded them. On a trifling or inconclusive experiment were built the most wonderful mechanisms. Their action was so clearly explained, and their effects so well understood, and so magnificent, “ that, by my faith," says a sturdy contemporary, when describing the class, “the very boldness of the projection made unsteady the judgment of right worthy men, who openly spoke, in other matters, their mean opinion of the artists." To Decaus, particularly, the praise of ingenuity and credulity applies in a wide extent; and the prolix earnestness with which he discusses some visionary projects, is only equalled by the apathetic brevity with which he dismisses some exquisite inventions. None of his fancies is so great a favourite as the mode of raising water by the sun's heat. In the “Epitre Dedicatoire," after giving a laconic summary of the contents of his folio, he particu

Grand Bretagne. A Londres, imprimé pour Thomas Davis, 1657.A fourth edition, with the same title, but without a date or name of the place where it was printed, is “par Isaac de Caus, Ingénieur et Architecte, natif de Dieppe." In this the experiments on steam and their diagrams are omitted. This was translated into English by John Leak, in 1707. The plates are the same as those in the edition of 1624. The diagrams and experiments on steam are omitted in the translation also.

SUN'S HEAT ENGINE.

29 larly draws the most Christian king's attention to his ingenious appropriation of the solar influence, by which he can perform marvellous effects : a machine acted on by a common fagot being possibly considered, by the “ architecte au roy," a thing too common to be noticed by so great a monarch.

The principle and arrangement of these whims have been already described ; the variations may here only be noticed. Instead of the ball in Hero's problem, Decaus (fig. X) substitutes a box for the water, with lenses inserted into its lid, to increase the sun's heat by concentrating the rays: and in another diagram he places the glasses in a frame, and throws the sunbeams on the outside. The pipe going from the cistern into the heated vessel, he furnishes with a valve opening upwards, to prevent the return of the water; another valve is placed in the pipe rising from the heated vessel, also to perform the same office; as might have been expected, the effect is greatly enlarged in the improved apparatus. Hero was satisfied to make the water he raised a small distance fall in drops ; Decaus elevates his to an imposing height, and it descends in copious jets, replenishing ample fountains.

These trifles need not detain us longer from the simpler things, which form his best claim to rememberance, as one of the earliest, though rude, experimenters on steam and appliers of its power to a purpose of utility and importance.

One of his rough experiments will readily recall the source of some later illustrations of the power of steam. A well-closed copper ball, which contains a little water, is placed on a fire; when heated, the “ compression of the steam within will burst the globe in pieces, with an explosion

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EXPERIMENTS ON STEAM. like that of a petard.* In another, he shows how heat carries off the water, into which it enters by evaporation; and, in a third, that steam returns by condensation into its own bulk of water ;t and

*"Soit une balle de cuivre d'une pied ou deux en diamètre, et espaisse d'un pouce laquelle sera remplie d'eau par un petit trou lequel sera bouche après bien fort avec un clou en sorte que l'eau ny air en puisse sortir, il est certain que si l'on met la dite balle sur un grand feu, en sort qu'elle devienne fort chaud qu'il se fera une compression si violente que la balle crevera en pièces avec bruit semblable à un petart.” Raisons, &c. p. 2.

4“Soit un vaisseau de cuivre rond marqué a, bien clos et soude toute à l'entour, auquel il y aura un tuyau marqué c, d, dont l'un de bouts, e, approchera du fond autant qu'il faut pour laisser passer l'eau, et l'autre bout, d, sortira dehors le vaisseau, auquel il y aura un robinet marqué c, pour ouvrir et fermer quand besoing sera, et y aura aussi un souspiral en haut marqué e, après faut mettre de l'eau dans le dit vaisseau par le souspiral jusques à une certaine quantité, et si le vais

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seau contient trois pots l'on y en mettra justement un pot après faudra mettre le dit vaisseau sur le feu viron trois ou quatres minutes, et laisser le souspiral ouvert puis retirer le dit vaisseau du feu, et un peu après faudra retirer l'eau dehors par le souspiral, et trouverez que partie de la dite eau s'est esvaporée par la chaleur du feu après faudra remplir la mesure du pot comme il estoit auparavant, et remettre l'eau dedans le vaisseau, et alors faudra bien boucher le souspiral et le robinet et remettre le vaisseau sur le feu aussi longten ps comme la première fois, puis le retirer et le laisser refroidir de soy-mesme sans ouvrir le souspiral, et après qu'il sera bien refroidir foudra retirer l'eau de dedans et y trouverez justement la mesme quantité que l'on y aura mise, tellement qu'il se peut voir que l'eau s'estoit s'esvaporée

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