TRACT 36.

THE WHIRLING-MACHINE.

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air : let us therefore inquire what this velocity is. Now thevelocity with which any fluid issues, depends on its altitudeabove the orifice, and is indeed equal to the velocity acquir-ed by a heavy body in falling freely through that altitude.But, supposing the height of the barometer to be 30 inches,or 2feet, the height of a uniform atmosphere, all of thesame density as at the earth’s surface, would be 2 ^ x 13*6X 833|- or 28333 feet; therefore \/l6 : V28333 : : 32 : 8v/28333 = 1346 feet, which is the velocity sought. Andtherefore, with a velocity of 1600 feet per second, or anyvelocity above 1346 feet, the ball must continually leave avacuum behind it, and so must sustain the whole pressure ofthe atmosphere on its fore part, as well as the resistancearising from the vis inertia of the particles of air stiuck bythe ball.

(11). On a review of the whole of the premises, we findthat the resistance of the air, as determined by the foregoingexperiments, differs very widely, both in respect to its quan-tity on all figures, and in regard to the proportions of its ac-tion on oblique surfaces, from thesame actions and resistancesas assigned by the most plausible and imposing theories,which have heretofore been delivered, and confided in byphilosophers. Hence it may be concluded, that all the spe-culative theories on the resistance of the air, hitherto laiddown, are very erroneous; and that it is from experiments,carefully and skilfully executed, that a rational hope can begrounded, of deducing and establishing" a true and usefultheory of the actions of forces, so intimately connected withthe numerous and important concerns in human life.

Proceed we now to relate the further progress of our ex-periments with the whirling-machine, on other bodies, andin other positions.

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