approximate number of, 112;
attract each other, 148, 317;
attracted by comets,360;
Bode's law, 230;
comparative sizes of, 118, 119;
distance of, from the Earth, 109-111;
distance of, from the Sun, 558;
how distinguished from stars, 111;
irregularity of motions of, 317-324;
Lagrange's theory of rigidity of, 531;
light of, derived from the Sun, 113;
minor, 229-244;
orbits of the four giant, 117;
orbits of the four interior, 114;
orbits have their focus in the centre of the Sun, 139;
orbits not exactly circles, 135;
orbits take the form of an ellipse, 136-138;
origin of, as suggested by the nebular theory, 526;
periodic times of, 139-143, 558;
relative distances of, 229;
uniformity of direction in their revolution, 120, 322;
velocity of, 139-142, 144, 146, 237

Plato (lunar crater), 89

Pleiades, 241, 416;
invisible in the summer, 416

Pliny, the tides and the Moon, 535

Plough, the, 28

Pogson, Mr., 390

Pointers in the Great Bear, 28, 411

Polar axis, 196

Polar caps on Mars, 218, 219

Pole, the, distance of from Pole Star lessening, 494;
elevation of, 195;
movement of, 492;
near a Draconis, 494;
near Vega or a Lyra, 494

Pole Star, 194;
belongs to the Little Bear, 412;
distance of, from the pole of the heavens, 412, 492, 494;
position of, 411;
slow motion of, 412

Pollux, 420, 480;
value of velocity of, 484

Pons, and the comet of 1818, 345

Posidonius, 87

Potassium in the Sun, 50

Praesepe, 422

Precession and nutation of the Earth's axis, 492-502

Proctor, and the stars in Argelander's atlas, 476

Prism, the, 45;
its analysing power, 46

Pritchard, Professor, stellar photographic researches of, 449

Procyon, 420;
value of velocity of, 484

Prominences on the Sun, 53-59

Ptolemy, his theory of astronomy, 6;
lunar crater named after him, 92

Q

Quarantids, the, 400

R

Radius of the Earth, 193, 512

Rainbow, the, 45

Ram, the, 420

Reflectors, 19, 21, 25

Refraction by the prism, 45

Refractors, 11, 14, 16

Regulus, 421, 479

Reservoir formed from tidal water, 538

Retina, the, and the telescope, 10, 11

Rhea, 559

Rigel, 418, 420, 480

Rigidity of the planets, 532, 533

Roberts, Dr. Isaac, and the nebula in Andromeda, 469;
and the nebula in Orion, 469

Roemer, and the velocity of light, 261

Romance, planet of, 151-154

Rosse telescope, the, 19, 20, 468, 470

Rotat