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air exactly or nearly equal. The above differences areperhaps as little as can be expected in comparisons of thiskind where the effects compared are so indeterminate.

As to the water machines, it is plain, that the quan-tity of air carried down cannot be greater, than the spacesbetween the drops or divided streams in the pipe cancontain ; and that though the air in these spaces must beconsidered as being compressed to a certain degree, yet itcannot be supposed compressed into two thirds of its na-tural volume, which would be necessary for making thecalculations of the wooden bellows and the blowing ma-chine to agree, because such a condensation would requirethe weight of a column of water of eleven or twelve feet,or the third part of such a column as is equivalent tothe pressure of the atmosphere ; whereas in the Dauphinymachine, though the air was pressed down with the fullforce of the column of water above the choak, the heightof this column is less than three feet, and could not con-dense it more than one twelfth part.

In what manner Reaumur computed the air of thewooden bellows, we have no account: it is probable thathe judged, as others have done in the fame cafes, fromtheir capacity ; supposing the whole quantity of air theycontained to be delivered at every stroke. If so, we canlay no stress on the computation, for neither the woodennor the leather bellows deliver their full contents ofair; a considerable space remaining full of air when thebellows are closed ; and this space containing considerablymore air than an equal volume of the atmosphere, on ac-count of the air being condensed in it by the pressure ofthe bellows. I have been informed by a judicious work-man, that the bellows of the iron finery retains commonlya third, and sometimes half of its air; and that when lined

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