[Book I

8 Division of the Subject.

sels for containing it; on Wells and fountains, and customs connectedwith them, &c.

Some persons are apt to suppose the term hydraulic machines, compri-ses every device for raising water; but such is not the fact. Apparatuspropelled by it, as tide mills, &c. are hydraulic machines; these do notraise the liquid at all; while on the contrary, all those for elevating it,which ,are comprised in the second dass, are pneumatic or hydro-pneumaticmachines, their action depending on the pressure and elasticity of the at-mosphere.

Th e first Class includes those, by which the liquid is elevated in movablevessels, by mechanical force applied to the latter.

Water raised in a bücket, suspended to a cord, and elevated by the hand,or by a windlass; the common pole and bücket, used daily in our rain wa-ter cisterns; the sweep or lever so common among our farmers, are exam-ples of this class; so are the various wheels, as the tympanum, noria,chain of pots; and also the chain pump, and its modifications. This Classembraces all the principal machines used in the ancient World; and thegreater part of modern hydraulic machinery is derived from it.

The second Class comprises such as raise water through tubes, by meansof the elasticity and pressure, or weight of the atmosphere; as suckingpumps, so named; siphons, syringes, &c.

The aplication of these machines, unlike those of the first class is limi-ted, because the atmosphere is only sufficient to support a column of waterof from thirty to thirty five feet in perpendicular height; and in elevatedcountries, (as Mexico ) much less. Numerous modifications of these ma-chines have been made in modern times, but the pump itself is of ancientorigin.

Those which act by compression are described in the third Class. Theliquid being first admitted into a close vessel, is then forcibly expelledthrough an aperture made for the purpose. In some machines this is effect-ed by a solid body impinging on the surface of the liquid; as the pistonof a pump: in others, the weight of a column of water, is used to accom-plish the same purpose.

Syringes, fire engines, pumps which are constructed on the same princbple as the common bellows, are examples of the former; and the famousmachine at Chemnitz in Hungary , Heron’sfountain, pressure engines, ofthe latter. Nor can the original invention of these be claimed by the mod-ems. Like the preceding, they were first developed by the energy of amcient intellects.

Fourth Class. There is however another class, which embraces severalmachines, which are supposed to be exclusively of modern origin;and some of them are by far the most interesting and philosophical of all.Such as the Belier hydraulique , or ram of Montgolfier; the centrifugalpump; the fire engine, so named because it raised water “by the help offire;” that is, the original steam engine, or machine of Worcester , More-land, Savary and Papin.

In thefifth Class, we have noticed such modern devices, as are eitherpractically useful, or interesting from their novelty, or the principles uponwhich they act. An account of siphons is comprised in this class. Re-marks on natural modes of raising water, Observations on cocks, pipes,valves, &c; and some general reflections are added.