CONTENTS. 



PART THE THIRD. PHYSICS. 



LECTURE XLI. 



ON THE FIXED STARS, 387. 



Division of the subjects of physics ; Astronomy, 387. Empty space, 388. 

 Fixed stars ; Light of the stars ; Figure ; Twinkling ; Number ; Magnitudes, 389. 

 Distances of the stars, 390. Clusters or nebulae ; Arrangement of the stars 

 in general ; Milky way, 391. Proper motions of the stars; Dr. Herschel's division 

 of stars and nebulae, 392. Changes of the stars, 393. Constellations ; Repre- 

 sentations of the stars ; Allocations, 394, 395. 



LECTURE XLII. 



ON THE SOLAR SYSTEM, 397. 



The sun a star ; Progressive motion of the sun, 397. Orbit of the sun ; Ro- 

 tation ; Spots, 398. Solar heat ; Sun's attraction ; Solar atmosphere, 399. 

 Planets ; Ecliptics, 400. Change of position of the ecliptic ; Nodes ; Keplerian 

 laws, 401. Rotation of the planets; Precession of the equinoxes ; Nutation of 

 the earth's axis ; Proportional distances of the planets, 402. Mercury ; Venus ; The 

 earth ; Mars, 403. Juno ; Pallas ; Ceres ; Vesta ; Jupiter ; Saturn, 404. Georgian 

 planet; Unknown planets; Satellites; Moon, 405. Satellites of Jupiter, 406. 

 Ring of Saturn; Comets, 407. Number and orbits of the comets, 408. 



LECTURE XLIII. 



ON THE LAWS OF GRAVITATION, 409. 



Newton's great discovery, 409. Attraction of spherical bodies ; Extent of the 

 force of gravity, 410. Sun's change of place ; Orbits of the planets ; Keplerian 

 laws ; Universality of gravitation, 411. Motions of the apsides and nodes ; 

 Changes of the ecliptic; Forms of the planets; Precession; Nutation, 412. 

 Lunar motions ; Disturbing force of the sun, 413. Acceleration of the moon's 

 motion ; Moon's rotation ; Orbits of comets ; Predictions of Halley and 

 Clairaut, 414, 415. 



LECTURE XLIV. 



. 

 ON THE APPEARANCES OF THE CELESTIAL BODIES, 415. 



Apparent motions to be described after the real ones, 415. Motions of the stars 

 and sun ; Motions of the earth ; Apparent revolution of the sun ; Sun's apparent 

 diameter, 416. Length of summer and winter ; Day and night ; Sun's apparent 

 path; Centrifugal force, 417. Places of the stars ; Twilight; Relative positions 

 and phases of the planets, 418. Phases of the moon ; Lunar eclipses ; Eclipses 

 of the sun, 419. Series of eclipses, 420. Harvest moon; Eclipses of Jupiter's 



