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Dr. Hales found that a smith’s bellows raised a mercu-rial gage about an inch, so that it would have raised awater-gage about fourteen inches. The twenty-fiveounces and a half, raised in M. Barthes’s experiment bythe blast of the machine of St. Pierre from an aperture ofan inch and a quarter bore, Englilh measure, are equiva-lent to the ascent of water in the gage pipe forty or forty-one inches. I have been informed, that the pipe bywhich the air is discharged into our iron furnaces is atleast of an inch and a half bore; and that the air, withthis aperture to pass off by, ought to be of as great densityas it can be reduced to by the human breath in a con-fined space; which is such as to raise the water in thegage about fifty inches; in which cafe it is compressedinto near an eighth part less volume than it commonlyoccupies in the atmosphere. But the quality of the fueland other circumstances occasion such variations in thisrespect, that no general standard can be laid down. I havebeen assured, that a charcoal fire will be excited as stronglyby such a blast as raises the gage thirty-six inches, as a sireof coaked pitcoal will be by one of fifty inches.

II. Observations on the air vessel.

The structure of the air vessel, or tub at the bottom,is in great measure independent of that of the rest ofthe instrument; the same air vessel serving equally for dif-ferent kinds and sizes of these machines, while the per-fection of the other parts consists in their adjustment andproportion to one another. The office of this vessel be-ing only to serve as a reservoir for the air, and to sufferthe waste water to pass off, no great care seems to beneedful for regulating its dimensions ; and as the stone,which is placed in it under the pipe, serves only to receive

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