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THE POPULAR SCIENCE MONTHLY.
tracted neck at the end connected with the pump, so as to readily admit of being sealed off at any stage of the exhaustion. D is the pump-gauge, and E is the barometer.
Fig. 1.
The whole being fitted up as here shown, and the apparatus being full of air to begin with, I passed a spirit-flame across the lower part of the tube at b, observing the movement by a low-power micrometer: the pith-ball (a h) descended slightly, and then immediately rose to
