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iirch'es in diameter, and spread out at top to the width ofsixteen or eighteen inches, that a large space may be lestround the cullender : this space should reach three or fourinches above the uppermost perforations of the cullender,to prevent any of the water from being dashed over the top.

A pit is to be funk in the ground, not less than six feetdeep. In this is to be placed an air vessel, made of woodlined with lead, without a bottom, three or four feet inwidth, and ten or eleven high. The vessel should be sup-ported on feet, of a proper strength, with fussicient spacesbetween them for the water to pass-freely out: this wayis preferable to the common one of placing the loweredge of the vessel on the bottom of the pit, and cuttingan aperture in the side, because the height of the apertureis so much taken off from that of the vessel. The reser-voir being fourteen feet above the ground, and the upperpipe and cullender reaching down eight feet, only sixfeet remain below the cullender ; so that the air vessel,having six feet sunk in the ground, will reach nearly upto the cullender, and almost the whole height of theundermost pipe will be included within the vessel. Thispipe may be above nine feet long, three feet or more ofit going down into the pit; which three feet are herean entire gain in the height of the fall, for the pipe inthe other machines comes at most no lower than thelevel of the ground where the water runs off on theoutside. This height is gained, in virtue of the com-pressed air in the vessel pushing down the water below,as already shewn in the second article of this section :it may be always as great as the height to which thewater is intended to rife in the gage. At the distance offive or six inches under the orifice of the pipe is to beplaced the concave iron plate or stone for the water tofall on. In the top of the air vessel is to be fixed the gageand the blowing pipe.

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