[ 3 J 4 ]

Such is the general construction of the blowing ma-chine, which promises to be particularly useful in caseswhere water is scarce, or where the want of a naturalfall renders it necessary to raise, by very expensivemeans, the great quantities requisite for working thecommon bellows. It is presumed, that one of these ma-chines will be sufficient for the iron forge, and forsundry other purposes where the quantity of air is notrequired to be very great; that it wilbbe less expensive,on account of the durability of its materials, and the sim-plicity of its structure, than any kind of bellows now inuse ; and what is of principal importance, that muchless water will serve for working it. In cases where oneof the machines cannot supply air enough, as for thelarge iron smelting furnace, two pipes may be used, bothfed by one reservoir, and entering into one air vessel, aspractised in some of the instruments described in the firstsection. The using of two pipes appears more eligiblethan enlarging the bore of one; for air cannot be so freelyintroduced into a large body of water, though divided intostreams by the cullender, as into two smaller ones ofequal quantity.

It may be observed, that the blast will be stronger in adense state of the atmosphere, than when it is more rareor expanded, a greater quantity of air being then intro-duced under an equal volume. If therefore the quantityof water has been adjusted so as to raise the gage to a pro-per height when the air was light, it will frequently hap-pen that the fame quantity of water shall raise it higher,and consequently, if no greater height is required, that apart of the water may be saved. As the gage of our ma-chine discovers by inspection these variations in its effect,the register affords convenient means of regulating itspower, and increasing or diminishing the quantity of water.

VI.