XV^ill SUMMARY OF THE CONTENTS. 



ill the orbits of the planets ; a rotating ring (the zodiacal light) and nit> 

 teoric stones, probably to be regarded as small cnsmical bodies. The 

 telescopic planets, Vesta, Juno, Ceres, Pallas, Astrea, Hebe, Iris, and 

 Flora, with their frequently intersecting, strongly inclined, and more 

 eccentric orbits, constitute a central group of separation between the 

 inner planetary group (Mercury, Venus, the Earth, and Mars) and the 

 outer group (Jupiter, Saturn, Uranus, and Neptune). Contrasts of these 

 planetary groups. Relations of distance from one central body. Dif- 

 ferences of absolute magnitude, density, period of revolution, eccentric- 

 ity, and inclination of the orbits. The so-called law of the distances of 

 tiie planets from their central sun. The planets which have the largest 

 number of moons — p. 96 and note. Relations in space, both absolute 

 and relative, of the secondaiy planets. Largest and smallest of the 

 moons. Greatest approximation to a primary planet. Retrogressive 

 movenieiit of the moons of Uranus. Libration of the Earth's satellite— 

 p. 98 and note. Comets ; the nucleus and tail ; various forms and di- 

 rections of the emanations in conoidal envelopes, with more or less 

 dense walls. Several tails inclined toward the sun ; change of form of 

 the tail; its conjectured rotation. Nature of light. Occultations of the 

 fixed stars by the nuclei of comets. Eccentricity of their orbits and 

 periods of revolution. Greatest distance and greatest approximation 

 of comets. Passage through the system of Jupiter's satellites. Comets 

 of short periods of I'evolution, more correctly termed inner comets 

 (Encke, Biela, Faye) — p. 107 and note. Revolving aerolites (meteoric 

 stones, fire-balls, falling stars). Their planetary velocity, magnitude, 

 form, observed height. Periodic return in sti-eams; the November 

 stream and the stream of St. Lawrence. Chemical composition of me- 

 teoric asteroids — p. 130 and notes. Ring of zodiacal light. Limita 

 tion of the present solar atmosphere — p. 141 and note. Translatory 

 motion of the w^hole solar system — p. 145-149 and note. The exist- 

 ence of the law of gravitation beyond our solar system. The milky 

 way of stars and its conjectured breaking up. Milky way of nebuloiis 

 spots, at right angles with that of the stars. Periods of revolutions of 

 bi-colored double stars. Canopy of stars; openings in the stellar stra- 

 tum. Events in the universe ; the apparition of new stars. Propaga- 

 tion of light, the aspect of the starry vault of the heavens conveys to the 

 mind an idea of inequality of time — p. 149-154 and notes. 



II. Terrestrial Portion of the Cosmos Page 154-359 



a. Figure of the earth. Density, quantity of heat, electro-magnetic 

 tension, and terrestrial light — p. 154-202 and note. Knowledge of 

 the compression and curvature of the earth's surface acquired by meas- 

 urements of degrees, pendulum oscillations, and certain inequalities in 

 the moon's orbit. Mean density of the earth. The earth's crust, and 

 the depth to which we are able to penetrate — p. 159, 160, note. Three- 

 fold movement of the heat of the earth ; its thermic condition. Law 

 of the increase of heat with the increase of depth — p. 160, 161 and note. 

 Magnetism electricity in motion. Periodical variation of terrestrial 

 magnetism. Disturbance of the regular course of the magnetic needle 

 Magnetic storms; extension of their action. Manifestations of magnet- 

 ic force on the earth's surface presented under three classes of phe- 

 nomena, nam'?ly, lines of equal force (isodynamic), equal inclination 

 (isoclinic), and equal deviation (isogenic). Position of the magnetic 

 pole. Its probable connection with the poles of cold. Change of all 

 the magnetic phenomena of the earth. Erection of magnetic observe 



