The first of which is, That an unequal pressure of the incumbent Air, will cause an unequal height in the water’s Surfaces.

And the second is, That in this experiment there is such an unequal pressure.

That the first is true, the following Experiment will evince.  For if you take any Vessel so contrived, as that you can at pleasure either increase or diminish the pressure of the Air upon this or that part of the Superficies of the water, the equality of the height of those parts will presently be lost; and that part of the Superficies that sustains the greater pressure, will be inferior to that which undergoes the less.  A fit Vessel for this purpose, will be an inverted Glass Syphon, such an one as is described in the Sixth Figure.  For if into it you put Water enough to fill it as high as AB, and gently blow in at D, you shall depress the Superficies B, and thereby raise the opposite Superficies A to a considerable height, and by gently sucking you may produce clean contrary effects.

Next, That there is such an unequal pressure, I shall prove from this, That there is a much greater incongruity of Air to Glass, and some other Bodies, then there is of Water to the same.

By Congruity, I mean a property of a fluid Body, whereby any part of it is readily united with any other part, either of itself, or of any other Similar, fluid, or solid body:  And by Incongruity a property of a fluid, by which it is hindred from uniting with any dissimilar, fluid, or solid Body.

This last property, any one that hath been observingly conversant about fluid Bodies, cannot be ignorant of.  For (not now to mention several Chymical Spirits and Oyls, which will very hardly, if at all, be brought to mix with one another; insomuch that there may be found some 8 or 9, or more, several distinct Liquors, which swimming one upon another, will not presently mix) we need seek no further for Examples of this kind in fluids, then to observe the drops of rain falling through the air and the bubbles of air which are by any means conveyed under the surface of the water; or a drop of common Sallet Oyl swimming upon water.  In all which, and many more examples of this kind that might be enumerated, the incongruity of two fluids is easily discernable.  And as for the Congruity or Incongruity of Liquids, with several kinds of firm Bodies, they have long since been taken notice of, and called by the Names of Driness and Moisture (though these two names are not comprehensive enough, being commonly used to signifie only the adhering or not adhering of water to some other solid Bodies) of this kind we