An introduction to astronomy: designed as a text-book for the use of students in college. By Denison Olmsted ...

ANALYSIS. XV
Art. Art.
Corona Borealis, Hercules, Lyra, Cyg- Result on comparing the places of cer
nus............................ 415 tain stars in ancient and modern
Vulpecula, Aquila, Antinous, Del- catalogues........................ 481
phinus, Peasus, Ophiuchus....... 415 Motion of the solar system in space.. 4,82
Southetn' C6onstellations.............. 416 Point toward which it is moving..... 432
Orion, Lepus, Canis Major........... 416 Rate of motion per annum.......... 4328
Canis Minor, Mlenoceros, Hydra..... 416 Examples of great annual proper moLesson for the middle of September'.. 417 tions........................ 433
Lesson for the middle of December. 417 DISTANCES OF THE STARs-how found. 434
Lesson for the middle of March..... 417 What is the base line for parallax?... 434
Lesson for the middle of June....... 417 Why it was supposed impossible to
determine a parallax of less than 1 " 434
SCpter 11.-DOaUBaLE STARS-CsTEMPORARYD DDistance implied by a parallax df 1". 4385
KSTA}1-VARIABLE; STARS-CLUSTERS AND Bessel's determination of the parallax
of 61 Cygni..................... 435
Use of great telescopes in studying His method of investigation......... 435
the stars......................... 418 Distance measured by the progress of
Herschel's forty-feet telescope....... 419 light and by a railway car, respecRosse telescope..................... 419 tively............................ 435
Pnlkova and Cambridge telescopes.. 419 Actual period of revolution of the
DOUBLE STARs-defined............. 420 components of 61 Cygni.......... 435
By whom discovered............... 421 Space described by the star annually. 435
Examples-number................. 421 Reliance to be placed on Bessel's deWhen merely optically double....... 421 termination...................... 435
When physically double............. 421 N2ature qf the Stars................. 436
System of' double, triple, and multiple Size of Sirius compared with the sun. 486
stars............................. 421 Proof that the fixed stars are suns... 437
Colors of the components.......... 421 End for which they were made...... 438
TEMPORARY STARS-defined.......... 422 Arguments for a plurality of worlds. 438
Examples.......422
VAMIIABLE STARS-defined.......... 423 Chapter IV.-SYSTEM OF THE WORLD.
Examples......................... 423 System of the world defined....... 439
Evidence of activity among the stars. 423 Complex character of early systems.. 439
CLsTERS-examples................ 424 Things known to Pythagoras........ 440
NEHBUL: —defitled.................... 424 HIis visionary notions............... 440
Examples —nebula of Andromeda.... 425 Rejection of his system.......... 441
Nebula of Hercules............... 425 Crystalline spheres of Eudoxus...... 441
Magellanie clouds......... 42 How the two motions were accounted
Ne'bula of Orion.................... 425 for............................... 441
Use of great telescopes for these ob- Hipparchus- truths discovered by
jects............................. 425 him............................. 442
Singular forms of nebulae........... 425 Almagest of Ptolemy............... 442
Resolvable and irresolvable distin- Ptolemaic System explained.......... 444
guished.............. 426 Illustrated by Fig. 81............... 445
Signs of beauty andl symmetry among Defects of this system...... 446
the nebull.e........... 426 Objections to it....... 447
Nebulous S'ta.s-defined............. 427 Copersican System explained........ 449
Annular e/buvl —defined............ 427 Arguments on which it rests........ 449
Example in Lyra.................. 427 Proofs that the planets revolve about
Planetary Nebtla.s.................. 427 the sun......... 449
Resemblance to planets-great extent. 427 Proofs of systems among the stars... 450
Example in Andromeda............. 427 Exemplified in the Pleiades, Nebula
Milky Way-cause of its peculiar of Hercules, Binary Stars, and Neblight............................. 428 ulse.............................. 450
Number of its component stars....:.. 428 Uniformity of plan in natural structures. 450
Chapter III,-MOTIONS oF THE FiXED
Chapter II-MToNs OF THE FIXED Ascending orders of systems deSTARS-DISTANcES-NATURE. srib450
scribed;..................... 450
Binary Stars-defined.............. 429 Supposed center of the universe..... 450
Number of these................... 429 Central sun-where placed........... 450
Periodic times-examples........... 429 Reasons fbr believing that all the
Law of gravitation among the stars.. 480 heavenly bodies are united in one
Proper Motions of the stars.......... 431 grand system.................... 451