384 FIXED STARS. SECT. XXXVI. 



SECTION XXXVI. 



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 Nebulas 



Globular Clusters Splendour of Milky Way Distribution of the 

 Nebulae The Magellanic Clouds Nebulae round ? Argus Consti- 

 tution 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 regis- 

 tered 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 geographical 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, a Centauri, and Arcturus are the 

 brightest stars in the heavens ; the others are classed according 

 to their apparent lustre, from the first to the seventeenth magni- 

 tudes. Capella, a Lyras, Procyon, and twenty or twenty-one 

 more, are of the first magnitude ; a Persei, y Orionis, a Cygni, 

 and in all fifty or sixty, are of the second ; and of the third there 

 are about 200, such as 77 Bootis and 77 Draconis, the numbers 

 increasing as the magnitude diminishes. Those of the eighth 

 magnitude are scarcely visible to the naked eye, and it requires 

 a very good telescope to see stars of the seventeenth. This 

 sequence is perfectly arbitrary ; but Sir John Herschel has ascer- 

 tained by actual measurement the comparative lustre of a great 

 many for example, he found that the light of a star of the sixth 



