_ s 2S4 ]

with wood, so that as little vacant space as possible mightbe left, he found it to blow much stronger than before.

The strength of bellows is best judged from the forceof the blast itself; and this force may be determined, inthe method recommended by Mr. Barthes, already men-tioned, by the weight it is capable of raising. He foundthat in the blowing machine of St. Pierre, described atthe end of the preceding section, the force of the blastissuing from a hole of an inch and a third in diameter,raised the arm of a balance loaded with a weight oftwenty-five ounces and a half. He gives some other ex-periments, of comparing the proportional diminution ofits force according to the diminution of the height of thewater; which I shall here insert in the original Frenchmeasures, to avoid unnecessary fractions. The above forceof twenty-five ounces and a half is the maximum of thismachine, produced by the full quantity of water in thebason, or a height of forty-eight inches above the choak :with a height of forty-one inches, the weight raised wastwenty-two ounces ; with a height of thirty-two inches,nineteen ounces; with a height of twenty-eight inchesand a half, seventeen ounces and a quarter ; with twenty-four inches and a half, fifteen ounces and a quarter; withnineteen inches, twelve ounces and three eighths; withsixteen inches and two thirds, ten ounces and a quarter;and with a height of thirteen inches and a half, eightounces and three quarters.

It may be observed, that in some of these experimentsthe water must have been employed to disadvantage ; and.that by increasing the height of the water much furtherthan the above limits, in the fame machine, we could notexpect to produce proportional augmentations of theforce of the blast : for if a certain quantity of water, run-ning with a certain velocity through the choak, be sup-posed