eculae, 317

"Oases" of Mars, 216, 220

Object-glass, 109

Oblate spheroid, 165

Occultation, 61-62, 202, 296

_Olaf, Saga of King_, 88

Olbers, 227, 253, 256, 271

"Old moon in new moon's arms," 185

Olmsted, 271

Omicron (or "Mira") Ceti, 307-308

Opposition, 209

"Optick tube," 108-109, 232

Orange (rays of light), 121

Orbit of moon, plane of, 63

Orbits, 32, 36-37, 66, 150, 157

Oriental astronomy, 107

Orion (constellation), 195, 279, 296-297, 316;
Great Nebula in, 316, 328

Oxford, 139

Oxygen, 145, 156, 166, 346

Pacific Ocean, origin of moon in, 339

Palitzch, 255

Pallas, 225, 227

Parallax, 57, 173, 280, 305, 320, 326

Pare, Ambrose, 264-265

Peal, S.E., 205

Peary, 277

Pegasus (constellation), 306

Penumbra of sunspot, 135

Perennial full moon of Laplace, 190

Pericles, 84

Perrine, C.D., 232-233, 315

Perseids, 270, 273-275

Perseus (constellation), 273, 279, 307, 312

Phases of an inferior planet, 149, 160;
of the moon, 149, 160, 183-185

Phlegon, Eclipse of, 85-86

Phobos, 223

Phoebe, retrograde motion of, 240, 250, 336

Phosphorescent glow in sky, 323

Phosphorus (Venus), 150

Photographic survey of sky, international, 290-291

Photosphere, 130-131, 134

Piazzi, 23

Pickering, E.C., 302

Pickering, W.H., 199, 205-206, 220-221, 240, 339-341

Pictor, "runaway star" in constellation of, 281-282, 320, 330

Plane of orbit, 36, 150

Planetary nebulae, 245, 315

_Planetary and Stellar Studies_, 331

Planetesimal hypothesis, 337-338

Planetoids. _See_ Asteroids

Planets, classification of, 229;
contrasted with comets, 247;
in Ptolemaic scheme, 171;
relative distances of, from sun, 31-32

Plato (lunar crater), 198

Pleiades, 284, 296-297, 307

Pliny, 169, 260

Plough, 284, 291-296, 302

Plutarch, 86, 89, 169, 181

"Pointers," 292

Polaris. _See_ Pole Star

Pole of earth, Precessional movement of, 176-177, 295, 298-299

Pole Star, 33, 163, 177, 292-296, 300-301

Poles, 30, 163-164;
of earth, speed of point at, 164

Pollux, 282, 297

Posidonius, 186

Powell, Sir George Baden, 96

Praesepe (the Beehive), 307

Precession of the Equinoxes, 177, 295, 298-299

Pre-telescopic notions, 55

Primaries, 26

_Princess, The_ (Tennyson), 334

Princeton Obser