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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.
![](http://upload.wikimedia.org/wikipedia/commons/thumb/2/26/On_an_inversion_of_ideas_as_to_the_structure_of_the_universe_Fig_13.jpg/500px-On_an_inversion_of_ideas_as_to_the_structure_of_the_universe_Fig_13.jpg)
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