. Bulletin. duced by a permanent increase Lin the atmospheric pressure, is less whenthe gas pressure in the coal is high, and greater when the gas pressure is low. Con-versely, when the atmospheric pressure falls—which condition is accompanied by anincrease in the escape of gas—and then remains at this point, either for some time orpermanently, the percentage of gas gradually decreases again, though it does not recedeas low as the original level, so long as the pressure remains constant; the increased out-flow of gas, due to the permanent fall in the pressure, is smaller when the gas pressurei
. Bulletin. duced by a permanent increase Lin the atmospheric pressure, is less whenthe gas pressure in the coal is high, and greater when the gas pressure is low. Con-versely, when the atmospheric pressure falls—which condition is accompanied by anincrease in the escape of gas—and then remains at this point, either for some time orpermanently, the percentage of gas gradually decreases again, though it does not recedeas low as the original level, so long as the pressure remains constant; the increased out-flow of gas, due to the permanent fall in the pressure, is smaller when the gas pressurein the coal is high, and greater when the gas pressure is low. (4) Should a sudden rise of atmospheric pressure be succeeded by a more gradualincrease, a slow acceleration of the gas outflow ensues; on the other hand, when a rapidfall in the barometer is followed by a more gradual one, the retardation of the gas out-flow proceeds slowly. NOVEMBER1 5 10 15 20 25 30,1 DECEMBER10 15 20 JAXCART 10 15 20 25 81. 12. —Curves showing relation between length of flame of a blower and variations in atmosphericpressure, November, 1885, to January, 1886, at Hanover mine, Westphalia. In no case, however, do the maxima or minima of the barometric curves correspondto maximum or minimum rates of outflow of the gas. TESTS AT HANOVER MINE. In 1885 Broockmana made an investigation at Hanover mine No. 2near Wattenscheid, Westphalia, to determine the effect of variationsin atmospheric pressure on the volume of gas from a blower. Theblower was connected to a tube, and the gas burned so a comparisoncould be made of variations in height of flame with variations inpressure as recorded on a barograph. The results are given in figure12, which shows a close connection between the two indicated by anincreased flow of gas at the time of diminished atmospheric pressure,as in the tests of mine air at Karwin and other places. Heise and Herbst6 have shown that notable pressures of the gasare obt
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