# Popular Astronomy: A Series of Lectures Delivered at Ipswich/Index

INDEX.

A.

Air, refraction by, 16.

Arcs of meridian, how measured, 60.

Areas, Kepler's law of, 102, 226.

Ascension, right, 185.

Attraction of a sphere, 222, 285; of earth on moon, 220; of sun on Jupiter, 223; of a spheroid, 242.

Axis of permanent rotation, 282.

B.

Base, measurement of, 47.

Bessel finds distance of fixed stars, 197, 214.

Bradley discovers aberration, 188.

C.

Cavendish experiment, 260.

Centrifugal force, 241.

Clairaut's theorem, 252.

Clock, use of in finding longitude, 65.

Comets, motion of, 227.

Commensurability of mean motions, effect of, 233.

Co-ordinates, 21.

Copernican system, 98.

D.

Day, sidereal, 41; variation in length of day, how explained, 71; solar, 121.

Degree, 28.

Diameters of earth, 62.

Dichotomization of moon, 148, 167.

Distance of planets from sun, 127; of moon from earth, 136, 166; of sun from earth, 144; of fixed stars, 192, 209.

Disturbing force, 229.

Diurnal motion of earth, 66.

E.

Earth, moves, 66; diurnal motion, 66; motion, how represented, 77; permanence of axis, 77; figure, 53, 60, 86; how caused, 70, 87; calculated, 247; dimensions, 54, 86; density, not uniform, 252; how found, 256, 285; mass, 266.

Ecliptic, 74.

Ellipticity of earth, 241.

Elliptic motion, 110, 226.Equatoreal instrument, 8.

Equinox, 119.

Equinoxes, precession of, 175, 199; caused principally by moon, 181, 201.

F.

Fluid, equilibrium of, 244.

Focus of ellipse, 101.

Force, meaning of, 128.

Forces, composition and resolution of, 108, 133.

Foucault, his pendulum experiment, 277; his gyroscope, 282.

G.

Great circle, 75, 89.

Gravity, how measured, 247.

Gravitation, law of, 130, 175, 199; evidence of theory of, 217.

Gyroscope, 282.

H.

Heavens, apparent motion of, 5.

Heliometer, 214.

Hipparchus discovers precession, 202.

Horizontal point, how found, 31.

I.

Inequality of long period, 233.

J.

Jupiter, figure of, 70; satellites eclipsed, 206; attraction of by the sun, 223.

K.

Kepler's laws, 101, 126, 226; inferences from, 130.

L.

La Place explains inequalities of long period, 233.

Laws of motion, 103, 218.

Lens, 18.

Light, aberration of, 188-204; velocity of, 206; reflection of, 31, 42 , refraction of, 13, 45.

Longitude, how found, 64, 85.

Lunar nutation, 203.

M.

Mars, parallax of, 149, 168.

Mass of planet, found—from motion of satellites, 268; from perturbations, 268; of moon, 269; of earth, 265; of sun, 266.

Measurement of earth's surface, 46.

Meridian, 23.

Microscopes of mural circle, 30.

Moon, its distance, 136, 166; its parallax, 142; its orbit, 143; illumination of by sun, 148, 167; attraction of by earth, 220; its variation, 230.

Motion, apparent, of heavens. 5; of sun, 73, 88; of planets, 91; laws of, 103, 218; of stars, 215; of solar system, 216.

Mural circle, 29, 42.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, 46T.

Telegraph, electric, used to find longitude, 65.

Temperature affects length of metal bars, 47; how compensated for, 48.

Tides, 269.

Torsion balance, 261.

Transit instrument, 23, 39.

Transit, 145; of Venus, 145, 169.

Triangulation, 46, 50, 80.

Trigonometrical survey, 46.

Tycho Brahe, his theory of the motions of the planets, 97.

V.

Variation, moon's, 230.

Velocity of, 208.

Venus, motion of, 91; phases of, 98; transit of, 145, 169.

Vertical, 15, 45.

W.

Weight of earth, 266; of sun, 266; of planets, 268; of moon, 269.

Wires of telescope, 18.

Z.

Zenith, 35.

Zenith Sector, 55, 82, 122.