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354 dn Introduction to a General Syftem Reproach to the Owner of any Waterworks to have fine Grotto- Work, Cafcades, and other Inventions of this Kind, and not to have Water to fupply them withal. But by this Supply I would not be underftood to mean a con tinual Cadence or Current of Water, that being to be had but in few Places, except on low Grounds, where Rivers, at leaft Rivu lets, have their Courfe: Nor can I readily fubfcribe to thofe that value no Cafcade or Fountain, except they play continually, fince that would be limiting Waterworks to a few Places only, and would be the debarring many a pleafant Situation of that which is one of the greateft Beauties of it; I mean that of fine Water, efpecially if to it be added the Cadence and Murmuring of Streams, in Grotto, Rock, Cafcade, and Fountain-Works, which, tho’ they do not play always, yet have their proper Times of Diverfion, in all hot and fultry Weather, and in the Lawns and other interme diate Spaces of Woods, Groves, and other Places of Delight; and the Experience we daily have of the vaft Quantities of Water that good Engines produce, (which when emptied into Refervoirs or Ponds, well clay’d, afford furprizing Quantities of Water, enough to fupply not only Cities and Towns, but alfo large Bafons of Water,) confirm what I offer on this Head. Now, for the better underftanding this Art, it will be requifite that the Owner and Projector be rightly inform’d how many In ches of Water his Engine or Spring will give in a Minute, or an Hour, and confequently how great a Quantity in twenty four Hours; that lo he may compute how wide his Cafcades, Fountains, or his other Expences of Water that are required may be, and how long the Supply that arrives in twenty four Hours will play : One or two Hours, at moft, in a Day, is generally fuppofed Sufficient; and for the Thicknefs of Water over a Cafcade, half an Inch is enough ; and from Preliminaries fo eftablifhed, may alfo be readily calcu lated, how much fuch Cafcades may be contra&ed and enlarged. To proceed to the Theory or Motion of Spouting Water, &c. The learned Gravefende, Book II. c Part x. Cap. 8. of his Ma thematical Elements of Natural c Philofophy, fays, That a Liquid fpouting 'vertically out of a Hole, arifes up with that Celerity, with which it would come up to the upper Surface of the^ Liquid, yet it never comes tip to that Height: Becaufe the Velocity of a Liquid increafes, when the Depth of the Hole below the Surface of the Liquid increafes, in the fame Ratio as the Celerity of the falling Body increafes, when the Space gone through by the Fall increafes; and it is remarkable, that in the Beginning their Velocities a re equal;