tube with guinea and feather
The resistance of the air to fallen bodies is not proportioned to the weight, but depends on the surface which the body opposes to the air. Now, the feather exposes, in proportion to its weight, a much greater surface to the air than a piece of gold does, and therefore suffers a much greater resistance to its descent. Were the guinea beaten to the thinness of gold-leaf, it would be as long, or even longer in falling than the feather; but, let both fall in a vacuum, or under the receiver of an air-pump, from which the air has been pumped out, and they will both reach the bottom at the same time; for gravity, acting independently of other forces, causes all bodies to descend with the same velocity.
An apparatus for performing this experiment is shown in the engraving: the coin and the feather are to be laid together, on the brass flap, A or B: this may be let down by turning the wire, C, which passes through a collar of leather, D, placed in the head of the receiver.
Provide a glass tube, open at each end; close the upper end by the finger, and immerse the lower one in a glass of water, when it will be seen that the air is material, and occupies its own space in the tube, for it will not permit the water to enter it until the finger is removed, when the air will escape, and the water rise to the same level in the inside as on the outside of the tube.
Hold the breath, and place the open neck of a phial, containing oil of peppermint, or any other essential oil, in the mouth, and the smell will not be perceived; but, after expiration, it will be easily recognised.
yet more cherubs