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That this effect is the consequence of the pressure of the liquid will be easily made manifest by showing that, as the pressure is increased, the air is proportionally contracted in its dimensions; and as it is diminished, the dimensions are on the other hand enlarged. If the depth of the goblet in the water be increased, the cork will be seen to rise in it, showing that the increased pressure, at the greater depth, causes the air in the goblet to be more condensed. If, on the other hand, the goblet be raised toward the surface, the cork will be observed to descend toward the edge, showing that as it is relieved from the pressure of the liquid, the air gradually approaches to its primitive dimensions.

(34.) These phenomena also prove, that air has the property of elasticity. If it were simply compressible, and not elastic, it would retain the dimensions to which it was reduced by the pressure of the liquid; but this is not found to be the result. As the compressing force is diminished, so in the same proportion does the air, by its elastic virtue, exert a force by which it resumes its former dimensions.