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Astronomical Dialogues.
Globe; which you are to suppose now to be millions of Millions of times greater than it really appears to be: Then you know, if you look round you on the Earth, its Surface will extend every way from your Eye, like a vast Plain; which will be under your Feet, and to which your Body will be perpendicular, or upright: this Plain stretching all round you every way as far as your Eyes can fee, in a flat open Country where no Hills interpose: Hemispheres.Or on the Surface of the Sea, will seem to divide or cut the Concave Orb of the Stars, or the Sky, into two Parts (which they call Hemispheres; the one seemingly above this Plain; which therefore they call the Upper, and the other apparently below it: Which therefore they call the Lower Hemisphere. Horizon.Such a Plain is this is call'd the Horizon: And if it be really that which any one's particular Eye makes upon any occasional View, 'tis call'd the Sensible Horizon: But if you imagine this Plain, as you may easily do, to pass through the very Center of the Earth on the Surface of which you then stand, 'tis called the Real or Rational Horizon; because that doth really or actually divide the Starry Regions into two equal Hemispheres; and both these Horizons are well enough represented by that wooden Cir-
cle,
