SECT, xxxvii.] OF THE FIXED STAES. 413 



SECTION XXXVII. 



The Fixed Stars Their Number The Milky Way Double Stars Binary 

 Systems Their Orbits and Periodic Times Colours of the Stars Stars 

 that have vanished Variable Stars Variation in Sun's Light Parallax 

 and Distances of the Fixed Stars Masses of the Stars Comparative Light 

 of the Stars Proper Motions of the Stars Apparent Motions of the Stars 

 Motion and Velocity of the Sun and Solar System The Nebulae Their 

 Number Catalogue of them Consist of Two Classes Diffuse Nebulae 

 Definitely formed Nebulae Globular Clusters Splendour of Milky Way 

 Distribution of the Nebula? The Magellanic Clouds Nebulas round tj 

 Argus Constitution of Nebulae, and the Forces that maintain them 

 Meteorites and Shooting Stars. 



GREAT as the number of comets appears to be, it is absolutely 

 nothing in comparison of the multitude of the fixed stars. 

 About 2000 only are visible to the naked eye ; but, when the 

 heavens are viewed through a telescope, their number seems 

 to be limited only by the imperfection of the instrument. 

 The number registered amounts to 200,000, their places are 

 determined with great precision, and they are formed into 

 a catalogue, not only for the purpose of ascertaining geo- 

 graphical positions by the occultations of the brightest 

 among them, but also to serve as points of reference for 

 marking the places of comets and other celestial phenomena. 

 Sirius, Rigel, Aldebaran, &c., are of the first magnitude; 

 those of the eighth magnitude are scarcely visible to the 

 naked eye, and it requires a very good telescope to show 

 those of the 17th. 



The stars are scattered very irregularly over the sky ; in 

 some places they are thinly dispersed, in others crowded 

 together, especially in the Milky Way, which derives its 

 brightness from the diffused light of myriads of stars : so 

 numerous are they in some parts of it that more than 



