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GRAVITY OF ATMOSPHERIC AIR.

Experiment IV.

If a conical wine-glass be filled with water, and covered witha loose piece of paper; on inverting the glass the water will bekept from falling by the upward pressure of the air.

Experiment V.

If a vessel be perforated with small holes at the bottom, butclosed at the top, the upward pressure of the air will keep waterwithin the vessel, as will appear by successively stopping andunstopping a small hole in the top.

The pressure of the air may be shown by means of the Air-pump.

Experiment VI.

Let the air be exhausted from a glass receiver placed on thepump, the vessel will be held fast by the pressure of the ex-ternal air.

Experiment VII.

Let a small receiver be placed under a larger one and both beexhausted; the larger will be held fast while the small onebeing protected from the pressure of the air may be easily moved.

Experiment VIII.

If the hand be placed upon a small open vessel, in such amanner as to close its upper orifice, it will be held down withgreat force, if the vessel be exhausted.

Experiment IX.

If the mouth of an open receiver be closely covered with apiece of bladder, and then exhausted, the super-incumbent air