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calculation gives, as the resistance of the compressed airmay occasion some retardation of the motion. Of theother machines, the descriptions are too imperfect or ob-scure for any computation to be made from them.

The water, issuing from the narrow throat of the funnelwith great velocity, is said to spread so as to fill thewider bore of the pipe, and to become frothy from themixture of air with it. The jet thus enlarged may beconceived as consisting of a multitude of slender streamsor drops, the intervals between them being occupied byair, which is continually supplied through the air holes,and pushed down by the succeeding drops or streams. Ithas therefore been reckoned, that the volume of air whichpasses down the pipe must be as much greater than thatof the water, as the transverse area of the jet, whenspread and reduced to drops in the pipe, is greater thanwhen it passed through the throat of the funnel. Circlesbeing to one another as the squares of their diameters, thearea of the pipe of the Lead-hills machine will be to thatof the funnels throat as eighteen to twelve and a quarter:the volume of air, according to the above principle, beingto that of the water in the fame proportion, and the quan-tity of water nearly 324 gallons in a minute, the quantityof air in a minute should be about four hundred seventy-sive gallons and a half, or 134000 cubic inches, or seven ty-leven cubic feet and a half. In the same manner, themachine of Dauphiny will be found to yield about 1080gallons, or upwards of 304000 cubic inches, or 176 cubicfeet, of air in a minute : so that by this way of reckon-ing, the Dauphiny machine, with near a fourth lesswater than that of Lead-hills, should produce more thana double quantity of air.

But tho’ this method of computation appears specious,it is not perhaps to be much depended on ; air, in differ-ent