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cnt circumstances, occupying very different volumes, invirtue of its great compressibility : nor is it certain thatthe bores of the pipes are sufficiently filled, so as to carrvdown the full quantity of air. It may be presumed, thatthe air, intermingled in the jet, is always in some degreecompressed by the water; so that the interstices betweenthe streams or drops contain more air than equal spacesof the atmosphere. It may be judged however from theabove comparison, that the wider the pipe is, in propor-tion to the funnel’s throat, provided the water runningthrough the throat will spread through the whole extentof the bore of the pipe, the more air will be carrieddown.

Mr. Barthes, the only person I know of who has ex-amined these machines philosophically, and endeavouredto improve them, gives a method, in the memoir above-quoted, of comparing the proportional quantities or forcesof the air in different blowing machines, on anotherprinciple. From considerations too abstracted to be hereparticularized, he deduces a general rule, that the produceof air will be in all cafes in proportion to the quantityand velocity of the water : lo that the quantity of waterand height of the fall being given in two machines, andthe volume or force of the air afforded by one of thembeing measured by experiment, the volume or force ofthe air in the other may be determined by the rule. Ac-cordingly he made several experiments of this kind intwo machines ; measuring the force of the air, when thewater in the bason was at different heights, by the weight,which the blast acting on the arm of a balance, was ca-pable of raising. Taking one of these experiments for astandard, he computed by the rule what the results ofthe others ought to have been ; but the experiments andcalculations agreed ill together. And indeed the rule

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