An historical and philosophical account of the barometer, or, weather-glass, wherein the reason and use of that instrument, the theory of the atmosphere, the causes of its different gravitation are assigned and explained. And a modest attempt from thence made towards a rational account and probable judgment of the weather / By Edward Saul, A.M.

  • Saul, Edward, 1677-1754.
Date:
1766
Catalogue details

Licence: Public Domain Mark

Credit: An historical and philosophical account of the barometer, or, weather-glass, wherein the reason and use of that instrument, the theory of the atmosphere, the causes of its different gravitation are assigned and explained. And a modest attempt from thence made towards a rational account and probable judgment of the weather / By Edward Saul, A.M. Source: Wellcome Collection.

    18/108 (page 18)
    From hence it follows, 1y?, That by ^he fubfiding of the Mercury from the Top of the Tube, the intermediate Space (be¬ ing ufually about fix or feven Inches) is left entirely void of Air> and this is abfo- lutely neceffary in a good Barometer, as well to give Liberty to the outward Air to exert its Force, as to give room to the Rife of the Mercury within the Tube, upon any Increafe in the Gravitation of the Air. 2d, If there be any Bubble of Air confined within the Cylinder of Mercury, it will by a conftant Endeavour to free itfelf from PreiTure, after fome little Time, difengage itfelf, and make its Way to the Top of the Tube ; and there rarefying and expanding into a larger Compafs, it will in fome mea¬ rn re defeat the Ufe and Exacfnefs of this Inftrument; upon which Account the true *Torricellian Tube, is not made entirely of a Cylindrical Form (as in the common Wea- iher-Glafs) but fpreads out into a large Bolt Head, or fpherical Cavity at the Top, fo that if there be any Air remaining in the Tube, it may have there fufficient Room to expand itfelf, without affedting or de- preffing the Mercury. 3d, From hence alio it farther appears, that the Mercury within the Tube is kept fufpended, by the Gravitation of the external Air upon the Surface of the ftagnant Mercury in the Bafon. To