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Dilatancy
to bring the bag into communication with a pressure-gauge, when the mercury shows that the pressure in the bag is only half of that of the atmosphere outside the bag.
Fig. 13.
Had the pinch been greater a vacuum would have been caused within the bag by the expansion of the interstices. As it is, however, the bag has maintained its rigidity.
Then, if the pressure-gauge is closed and the neck opened, so that water may be drawn in, the
