[6] A vacuum.
[8] Thirty-two degrees is the point at which water begins to freeze, or ice to thaw.
[9] Evaporation.
[10] The two thus combined making a hygrometer: for which some kinds of hair, grass, or seaweed may be a make-shift.
[11] It stands lower, about a tenth of an inch for each hundred feet of height directly upwards, or vertically, above the sea; where its average height, in England, is 29·94 inches (at 32°).
[12] In an Aneroid, a metallic, or a wheel barometer, the hand's motion should correspond to that of mercury in an independent instrument.
[13] Southerly in South latitude.
[14] In the best columns, those of standards for example, no concavity is seen, at any time: but it is otherwise with many barometers, which do show a concavity.
[15] In these cases there is usually a combination or a contest of currents in the atmosphere, horizontally, or one above the other, or diagonally.