Observations on the device of Decaus.

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Chap. 4.]

were most likely mere trifles—whims that suited the taste of the age.No. 189 is probably one of them, which a contemporaneous English authoradduces under “ Experiments of mocions by rarefying water with fier,”.and of which he also observes, other devices may be derived from it.

Decaus appears to have read and traveled much, and to have collectedknowledge from every source within his reach. He describes saw-millsthat were used in Switzerland , fire-engines of Germany , cahal-loeks whichhe noticed between Venice and Padua : he cites Tacitus , Pausanias andPliny ; quotes largely from Heron, and refers his more learned readers toArchimedes , a commentary upon whose writings he promises to undertake.Of course he was acquainted with the works of Porta, for this Neapolitanphilosopber and his writings were greatly celebrated throughout Eu-rope. Now had Decaus turned his thoughts at all to the elevation of waterby steam, he would at once have perceived the advantages of a devicelike No. 1S7, by which the liquid could be raised in unlimited quantitieswithout being heated at all, as well as under all possible circumstances :and having perceived this, would he not (if the project of thus raisingwater had ever entered his head) have given it, or a modification of it,instead of No. 188 1 It is clear that he wanted an illustration of a propo-sition merely, and the one he has given he considered as good as anyother.

As long as the Natural Magic and the Spiritali of Porta are admittedto have been published, the former about fifty and the latter at least tenyears before the work of Decaus, there is little if any thing whereon tofound a claim for the latter. If we were to concede, what certainly is not“established beyond dispute, that the first idea of raising a weight by meansof the elastic power of steam belongs to the French author,” th efact wouldstill remain that the Neapolitan had long before shown how this could bedone ; and M. Arago has himself observed, that “ in the arts, as in theSciences , the last comer is supposed to be acquainted with the labors ofthose who preceded him—all denial in this respect is without value.” Theobject of Porta in introducing the device referred to was not to show itsapplication to raise water, and it is not fair to conclude that he was igno-rant of its adaptation for that purpose because he has not gone out of hisway to point it out. It has also been objected, that his apparatus raisedthe liquid to a very limited height. We do not know that Decaus’s didmore, for we are only told that the Contents of the ball would be drivenout, without the slightest intimation of an elevated discharge. Well, (anadvocate of the latter will say) but his apparatus is capable of raising wa-ter to all heights. And so is Porta’s. But had Porta “ the least idea ofthe great power which steam is susceptible of acquiring V’ The extractswhich we have given from his Natural Magic, on the rupture of vesselsby steam, prove that he was well aware of it; and the book from whichthese extracts are taken was his earliest production, being published in1560, at which time (he observes in the preface) he was only about fifteenyears old. To conclude, we are constrained to embrace the opinion, not-withstanding the arguments and eloquence of M. Arago, that the devicedescribed by Decaus brought to light no new fact, and gave rise to no newor useful result.

Although instances rarely occur in the arts in which the elevation ofhot water by the steam evolved from it could be of Service, there are some,as in chemical manipulations, in a few breweries and distilleries, and alsoin soap manufactories. The Operation in the latter is worth noticing:—In the ordinary process of manufacturing common hard soap, three or fourtons are often made at once in a deep iron vat or b§iler. Into this several