OF CONTENTS. Vll 



clusters of stars ? p. 13 (note , p. 22, and p. 23, note *). Historical 

 particulars p. 14 (note *, p. 28). Number of nebulae whose positions 

 are determined p. 26 (notes * and t). Distribution of nebula; and 

 clusters of stars in the northern and southern hemispheres p. 27 ; 

 spaces poor in nebulae, and the maxima of accumulation p. 28, and 

 note *. Configuration of nebulae: spherical, annular, spiral, and plan- 

 etary nebula? p. 31. Nebula (cluster of stars) in Andromeda p. 16- 

 31 (note t, p. 31); nebula in Orion's sword p. 17-39 (notes *, p. 18, 

 t, p. 23, , p. 36, *, p. 38, , p. 39, and *, p. 40) ; large nebula round rj 

 Argus p. 40 ; nebula in Sagittarius p. 41 ; nebula in Cygnus and Vul- 

 pes ; spiral nebula in the northern Canes Veuatici p. 41. The two Ma- 

 gellauic Clouds p. 43 (note *, p. 48). Black spots or Coal-sacks p. 51. 



(3. The Solar region ; planets and their moons, ring of the zodiacal 

 light, and swarms of meteor-asteroids p. 53-88. 



I. The Sun considered as a central body : Numerical data p. 59 (note 

 *, p. 59, and p. 62, note *). Physical constitution of the surface; en- 

 velopes of the dark solar globe ; Sun-spots, faculae p. 61. Diminutions 

 in the daylight recorded by the annalists ; problematic obscurations 

 p. 73, and note. Intensity of the light in the center and at the edge 

 of the Sun's disk p. 79, and note; also p. 81, note *.. Correlation of 

 light, heat, electricity, and magnetism; Seebeck, Ampere, Faraday 

 p. 84. Influence of the Sun's spots upon the temperature of our at- 

 mosphere p. 80. 



II. The Planets : 



A. General comparative considerations : 



a. Principal Planets : 



1. Number and epoch of discovery p. 89. Names, planetary 

 days (week), and planetary hours p. 92, and note t; also 

 p. 94, note *. 



2. Classification of the planets in two groups p. 102. 



3. Absolute and apparent magnitudes; configuration p. 105. 



4. Order of the planets and their distances from the Sun; the 

 so-called law of Titius ; old belief that the cosmical bodies 

 which we now see were not all visible from the beginning ; 

 Proselenes p. 106, note *, p. 1 08, and p. 120, note *. 



5. 'Masses of the planets p. 118. 



6. Densities of the planets p. 1 19. 



7. Periods of sidereal revolution and axial rotation p. 120. 



8. Inclination of the planetary orbits and axes of rotation ; 

 their influence upon climate p. 121, and note t, p. 126. 



b. Secondary planets p. 127. 



B. Special consideration ; enumeration of the individual planets and 

 their relation to the Sun as central body. 



The Sun p. 135-137. 



Mercury p. 137, 138. 



Venus; spots p. 138-141. 



The Earth; numerical relations p. 141. 



