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17.   Portrait of Tycho   41 18.   Early out-door Quadrant of Tycho   43 19.   Map of Denmark, showing the Island of Huen   45 20.   Uraniburg   46 21.   Astrolabe   47 22.   Tycho's large Sextant   48 23.   The Quadrant in Uraniburg   49 24.   Tycho's Form of Transit Circle   50 25.   A Modern Transit Circle   51 26.   Orbits of some of the Planets drawn to scale   60 27.   Many-sided Polygon or Approximate Circle enveloped by Straight Lines   61 28.   Kepler's Idea of the Regular Solids   62 29.   Diagram of Equant   67 30.   Excentric Circle supposed to be divided into equal Areas   68 31.   Mode of drawing an Ellipse   70 32.   Kepler's Diagram proving Equable Description of Areas for an Ellipse   71 33.   Diagram of a Planet's Velocity in Different Parts of its Orbit   72 34.   Portrait of Kepler   76 35.   Curve described by a Projectile   82 36.   Two Forms of Pulsilogy   87 37.   Tower of Pisa   91 38.   View of the Half-Moon in small Telescope   97 39.   Portion of the Lunar Surface more highly