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does not seem to be applicable but in circumstances,which can scarcely be expected to occur ,- for it supposesthe machines to be all perfect, and every drop of thewater to have its utmost effect, or to carry down with itas much air as it is capable of doing ; which cannot beadmitted to be the cafe in any of the blowing machinesyet constructed.

In the art des forges are mentioned some observations ofReaumur of the quantity of air afforded by the woodenbellows. He finds that those used at the iron furnacesyield 98280 cubic inches, or upwards of five cubic feet ofair at every stroke; and, including the two bellows, whichact alternately, 240 strokes in a quarter of an hour; which,on a reduction of the French measures to the English,make 1301896 cubic inches, or upwards of 753 cubicfeet, in a minute : this quantity exceeds that which theforegoing calculation gives for the machines of Dauphinyabove four times, and therefore four of the machinesshould scarcely be able to supply the iron furnace withso much air as the wooden bellews does; whereas twoor three are said to be sufficient. Again, the bellows ofthe iron finery and forge was found to give two thousandfisty-one cubic inches and a third at each stroke, and fourhundred and twelve strokes in a quarter of an hour ;whence the quantity of air in a minute is 458247 cubicinches, or somewhat more than 265 cubic feet: this isgreater than the calculation of the water machine, in theproportion of about three to two, tho’ one of the watermachines is found to supply the office of the bellows.

It is not to be supposed, that the quantity of air, whichfurnaces require, is confined to any such precise limits,as that two bellows, from their being found to answersufficiently for one kind of furnace, or even for one indi-vidual furnace, can be concluded to yield quantities of

2 air