Page:Popular Science Monthly Volume 7.djvu/704

684 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.



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