Chap. 6.] Three and four way Cocks. 433

since tbe man had abundant time to attend the fire in the intervals of turn-in g the cocks.

Notwithstanding the comprehensive sketch that Worcester has givenof this machine, a variety of opinions prevails respecting some of its parts,and the arrangement of the whole. In these respects scarcely two writersagree, while some differ widely. Some have supposed it to have consistedof two eolipiles, like those of Heron or Decaus, (Nos. 179 and 188) con-nected to one ascending pipe, (see Gralloway on the Steam-Engine )—anidea , we think, entirely out of the way, since such a plan would possessneither “ merit ” nor “ originality,” which the writer just named accordsto Worcester ’s device. It is moreover opposed to the description given,which expressly States that the contents of one vessel rarefied by fire,driveth up forty of cold water; whereas, by the supposed construction,all the water must have been heated to the boiling point before it couldhave been elevated at all, and to a temperature still higher before it wasraised forty feet.

The principal point undetermined is the mode by which the receiverswere charged. Were they so placed that the water flowed into themthrough a pipe and cock 1 Or, were they wholly immersed in the tank,well or pond, and furnished with valves opening inwards for the admis-sion of the liquid, and to prevent its return when the sfeam was turnedon l Or, were they placed above the water, and charged by atmosphericpressure 1 The first and second modes have been suggested, becauseWorcester says he did not raise the liquid by “ suckingbut it does notappear that he meant any thing more than that the contents of the receiversWere not expelled from them in this way. As the elevation to whichwater could be raised at one lift by his machine was only limited by thestrength of the vessels, he very naturally observed, to remove an objectionwhich he foresaw might be made tö his assertion, that this was not effectedby sucking, but by forcing the liquid up. His plan bears the same relationto a forcing pump, as using steam to produce a vacuum in a receiver doesto a sucking one ; and in distinguishing between the two applications ofthe vapor to raise water, viz. by its condensation and its expansion, heuses the same terms that we do to show the difference between the twoInstruments just named. Of a forcing pump we say, it does not raisewater by atmospheric pressure, but in Opposition to it; and that the ele-vation is only limited by the strength of the materials and the power em-ployed : now every person acquainted with the subject knows, that it isthe expulsion of the water from the cylinder that is referred to, not themode of filling it; for almost invariably are the vessels or cylinders offorcing pumps charged by sucking, and so they were in Worcester ’s time.

If the receivers were placed below the reservoir that supplied them,and were fed from it by a pipe, then as there were but two cocks used,they must have been such as are known by the term “ three-way,”—onepassage to supply steam to each of the receivers, and the other water.There is no dimculty in admitting this, for both three and four way cockswere in use ages before Worcester ’s days. They are described in thebpiritalia, (problem 31) in Besson’s Tbeatre, Fludd’s Simia, (see our 160thIllustration, page 354) Ozanam’s Recreations, and in several other old au-thors. One form of them is seen at page 421. Tavernier found, in bathsof the east, cocks which at the same mouth supplied “ either hot water orcold,” (Relation of the Seraglio) and they are described and figured in theForcible Movements of Decaus : thus prop. xix of Leak’s translation is“ Of the cock with four vents,” and its application is shown in a self-acting“ Phneumatique Engine.” M. Arago is therefore greatly mistaken, in his

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t.