OF CONTENTS. IX 



Number, p. 222. Order recognizable in apparent irregularity; great 

 differences of brightness; periods within periods, p. 226. Argelander's 

 table of the variable stars with commentary, p. 232. Variable stars in 

 undetermined periods (rj Argus, Capella, stars of the Ursse Major and 

 Minor), p. 246. Reference to the possible changes of temperature en 

 the Earth's surface, p. 246. 



V. Proper motion of the fixed stars, dark cosmical bodies, parallax ; 

 doubts as to the assumption of a central body for the entire heaven of 

 fixed stars : Change of the physiognomy of the sky, p. 248. Amount 

 of the proper motion, p. 251. Evidence in favour of the probable 

 existence of non-luminous bodies, p. 253. Parallax and measurement 

 of the distance of some fixed stars from our solar system, p. 255. 

 The aberration of light may be applied to the determination of the paral- 

 lax of double stars, p. 264. The discovery of the proper motion of the 

 fixed stars has led to the knowledge of the motion of our own solar 

 system, and even to the knowledge of the direction of this motion, 

 pp. 251 and 264. Problem of the situation of the centre of gravity of 

 the whole heaven of fixed stars and central suns? p. 267, and note 38 

 and 39.) 



VI. Double stars, period of revolution of two suns round a common 

 centre of gravity : Optical and physical double stars, p. 272; number, 

 p. 273. Uniformity and difference of colour; the latter not the conse- 

 quence of optical deception, of the contrast of complementary colours, 

 p. 282, notes 15 21. Change of brightness, p. 285. Multiple com- 

 binations (three to six fold), p. 285. Calculated orbitual elements, half 

 major axis and period of rotation in years, p. 289. 



VIT. Nebula, Magellanic Clouds, and Coal-sacJcs: Resolvability of 

 the nebulae ; questions as to whether they are all remote and crowded 

 clusters of stars? p. 291 (note 25 and 26). Historical particulars, p. 293 

 (note 44). Number of nebulae whose positions are determined, p. 309 

 (notes 35 and 36). Distribution of nebulae and clusters of stars in the 

 northern and southern hemispheres, p. 311 ; spaces poor in nebulae, and 

 the maxima of accumulation, p. 312, and note 41. Configuration of 

 nebulae : spherical, annular, spiral, and planetary nebulae, p. 317. Nebula 

 (cluster of stars) in Andromeda, pp. 295 318 (note 46) ; nebula in Orion's 

 sword, pp. 297329 (notes 12, 27, 61, 63, 67, and 68); large nebula 

 round rj Argus, p. 331; nebula in Sagittarius, p. 333; nebula in Cygnus 

 and Vulpes ; spiral nebula in the northern Canes Venatici, p. 323. The 

 two Magellanic Clouds, p. 335, (note 88). Black spots or Coal-sacks, 

 p. 347. 



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

 ~ ', and swarms of meteor -asteroids, p. 351 401. 



I. The Sun considered as a central body: Numerical data, p. 361 

 (note 4 6). Physical constitution of the surface; envelopes of the dark 

 solar globe; Sun-spots, faculse, p. 362. Diminutions in the daylight 



