N.
Nutation, 186, 202.
O.
Observations, how made, 18; with transit instrument, 26, 34; with mural circle, 31, 35.
Orientation, 122.
P.
Parabola, 130, 228.
Parallax, what, 114, 142; of moon, 136, 142, 161; of sun, 144, 166; how calculated, 173; of fixed stars, 195.
Pendulum, a measure of gravity, 248; Foucault's, 277; used to measure density of earth, 286.
Permanent axis of rotation, 78.
Perpendicular, 15, 44.
Perturbations, 229; of the moon, 229; of the planets, 232, 238.
Planets, motions of, 91, 122; their orbits, 101, 151; why they do not fall into or depart from the sun, 112, 132; perturbations of, 233, 238.
Plumb-line, direction of, 82.
Pole, how found, 33; its change of position, 204.
Pole star, 6, 25, 204.
Precession of equinoxes, 175, 199; caused by sun, 176, 199; and moon; 181, 201.
Pressure of fluids, 244.
Prism, effect of, on direction of a ray of light, 14.
Proper motion of stars, 215.
Ptolemaic system, 92, 124.
R.
Reflection of light, 31, 42.
Refractior, 13, 45; effect of, how avoided, 140.
Resolution of forces, 108, 133.
Retrograde motion, 124.
Right ascension, 185.
Rising of heavenly bodies, 5.
Römer discovers velocity of light, 208.
Rotation of earth, 66, 87; of top, illustrates precession, 184; composition of, 279.
S.
Schehallien experiment, 256
Sector, Zenith, 55, 82, 122.
Sidereal day, 41.
Sphere, attraction of, 222, 285.
Spheroid, 60; attraction of, 242.
Stars, apparent motion of, 5; how affected by aberration, 190; proper motion of, 215; distance of, 192, 209.
Stationary points of planets, 92.
Sun, apparent motion of, 71; distance of, from earth, 144, 166; from planets, 127, 146.
Survey, trigonometrical, 46