Hydrostatical and pneumatical lectures ... / Published with notes, by ... R. Smith.

  • Roger Cotes
Date:
1738
Catalogue details

Licence: Public Domain Mark

Credit: Hydrostatical and pneumatical lectures ... / Published with notes, by ... R. Smith. Source: Wellcome Collection.

    43/290 page 21
    From thefe experiments I might now in a few words and very eafily deduce thofe inferences, for whofe fake they were chiefly propofed, were they not already too obvious to be infilled on. I will therefore only mention them. Suppofing then the air to be an heavy fluid, and that the furface of the earth is as much preffed upon by this fluid as if it were every where covered with quickfilver to the height of about 29 inches and an half, or with water to the height of about 34 feet, as wTe fhall hereafter prove; if in thefiril experiment, Fig. 7, we fubfti- tute air inftead of water, and inftead of the plate of brafs applied to the orifice of the glafs veffel, two po- lifhed planes applied together fo clofely as to exclude the air from getting between, the lower plane mufl of neceftity be preffed againft the upper and kept fuf- pended. So in the laft but one of thefe experiments, in which the quickfilver was raifed above its level in the two pipes. Fig. 10, if we fubflitute the body of a pump for either of thofe pipes, water in the well for quickfilver in the veffel, air incumbent upon the water in the well for water incumbent upon the quick¬ filver in the veile], and obferve that as the water in our experiment was hindered from entering into the tinged water within the legs; but other equal parts of this plane on the outfides of each leg, will be unequally preffed by their incum¬ bent columns though of equal altitudes; becaufe the columns of the higher cup confift of more water and lefs oyl than thofe of the lower. The heavier columns will therefore prefs up the higheiwa- ter into the leg in its. cup, with greater force than the lighter co¬ lumns can prefs up the lower water into the leg in its cup, and the excefs of the former preffure above the latter will drive the wa¬ ter along the fyphon from the higher cup to the lower. This excefs of preffure, which caufes the flux, is therefore as the difference in weight of two columns compofed of water and oyl, whofe common bafe is equal, to the orifice of the fyphon, and com¬ mon height is the difference of the heights of the water in the cups? y
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