Page:Practical astronomy (1902, John Wiley & Sons).djvu/15

CONTENTS. Vll PAGrf 3. To Make the Axis of the Telescope Parallel to the Frame 56 4. To Make the Mirrors Parallel, when the Reading is Zero 57 Errors of the Sextant. Index Error 57 Eccentricity 58 The Astronomical Triangle 58 11. Time by Single Altitudes. 1st Method. To Find the Error of a Sidereal Time-piece by a Single Alti- tude of a Star (Form 3) 59 3t The Correction to be Applied to the Mean of the Altitudes. . 60 To Ascertain what Stars are Suitable for this Method 63 2d Method. To Find the Error of a Mean Solar Time-piece by a Single Altitude of the Sun's Limb (Form 4) 64 HI. Time by Equal Altitudes. 1st Method. To Find the Error of a Sidereal Time-piece by Equal Alti- tudes of a Star (Form 5) 66 2d Method. To Find the Error of a Mean Solar Time-piece by Equal Alti- tudes of the Sun's Limb (Form 6) 67 4 1 Correction for Refraction 68 3? Equation of Equal Altitudes 69 Time of Sunrise or Sunset 70 Duration of Twilight 70 LATITUDE. Form and Dimensions of the Earth 72 The Eccentricity of the Meridian 74 The Equatorial and Polar Radii 74 The Radius of Curvature of the Meridian at the Observer's Station 75 The Length of a Degree of Latitude 75 The Length of a Degree Perpendicular to the Meridian 75 The Length of a Degree of Longitude 76 The Length of the Earth's Radius at any Point 76 The Reduction of Latitude 77 Latitude Pi-oblems. 1st Method. By Circumpolars , 78 2d Method. By Meridian Altitudes or Zenith Distances 78 3d Method. By Circum-meridian Altitudes 79 Formula for Reduction to the Meridian 79 Method of Making and Reducing Observations 80 Hour Angle and Correction for Clock Rate 81 By Circum-meridiaa Altitudes of the Sun's Limb (Form 7). . 83 By Circum-meridian Altitudes of a Star (Form 8) 84