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 169)
of the visible Semediameter of the Earth, as increased by the Effect of the Refraction, or by the Distance of the Point P or P from Q or from the Surface of the Earth.
 20. Let the right Line AECIA be perpendicular to the Diameter oCN. And let the Arc AI or EA in the heavenly Sphere subtend an Angle of 1[[degree symbol]] is, in reference to an Eye placed at the Distance CH over-against C perpendicularly to the Plan of this Figure; that is, an Angle equal to twice the Refraction of Light in our Atmosphere. And upon the Diameter EI conceive the Circle EKKI whose Center is C. And I say that if a fixed Star should be supposed to describe behind the Earth consider'd as unmovable the right Line AECIA, it will appear almost as unmovable near the Point A, seeming to slacken its Course gradually there, till the Star itself, in about two Hours Time, has reached the Point I: And then, and not before, it will disappear in A. 
  21. But as ^[[soon as]]the Star comes to the Point E, its Image will appear suddenly in the opposite Point A, upon the Circumference of the apparent Disc of the Earth: From whence or the neighboring Points it will not depart, till the Star itself has actually reached the same Point A. Whereabout having seemed to continue all the while that the Line ECIAZz is describing; that is for about two Hours, the Star itself coming at last to Z or z will then go on full speed and pursue its Course.
   22. And so, all the while that the Star, or any other the like Lucid Point, as seen from the erected Point H, describes the Line EI; the Star will appear almost unmovable near A and