A supplement to Ures Dictionary of Arts, Manufactures, and Mines, : containing a clear exposition of their principles and practice. . rometer being exactly balanced against the weight of a column of air of the samediameter, reaching from the surface of tiie earth to the extreme limits of the length of this column of mercury is never more than thirty-one inches; below thatpoint it may vary, according to conditions, through several inches. There have been many useful applications of the barometer, but the only one with whichthis dictionary has to deal appears to be the following:—
A supplement to Ures Dictionary of Arts, Manufactures, and Mines, : containing a clear exposition of their principles and practice. . rometer being exactly balanced against the weight of a column of air of the samediameter, reaching from the surface of tiie earth to the extreme limits of the length of this column of mercury is never more than thirty-one inches; below thatpoint it may vary, according to conditions, through several inches. There have been many useful applications of the barometer, but the only one with whichthis dictionary has to deal appears to be the following:— Barometer, MackwortlCx Undcrciround.—In the goafs, or old workings, of some mines,hollows exist, in which explosive or noxious gases tend to accumulate in considerable quan-tity. When the barometer falls, these gases expand and approach or enter the workingplaces of the mine, producing disastrous results to life or health. To enable the managerof a mine to foresee these contingencies, he has but to construct a small model of such acavity, and let the expansion or contraction of the gas measure itself. In Jiy. 49, a is a 49. brass vessel, 12 inches long and 1^ inches in diameter, closed at each end. In one end isinserted a copper tube, ^ inch in diameter and 12 feet long, b. A hole, 2 inches in diam-eter, being bored 12 feet deep into the solid coal or rock, the brass vessel is pushed to thebottom of it, and the small tube is closely packed round with coal or clay, c is a glasstube, 4 feet long and \ inch in diameter, in which is placed water or oil. As the externalatmosphere presses, the surface of the liquid rises or falls, and the scale is graduated bycomparison with a standard barometer. The air contained in the brass vessel a, and coppertube B, is unaffected, or^early so, by temperature, and no correction has to be made for thelatter as in the sympiesometer. a and b may be conveniently filled with nitrogen, to pre-vent the oxidation of the metal; and the surface of the
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Keywords: ., bookcentury1800, bookdecade1860, bookpublishernewyo, bookyear1864
