DISTRIBUTION OF THE STAES. 181 



that of the Milky Way, we are entirely ignorant of its extent, 

 and have not the least idea of the external form of this im- 

 mense .system. 



The two opposite points of the celestial sphere around 

 which the stars are observed to be most sparse, have been 

 called the Galactic Poles; and the great circle at right 

 angles to the diameter joining these points, has been de- 

 nominated the Galactic Circle. For convenience, we will 

 express the distance of different points of the firmament 

 from the galactic circle, in either hemisphere, by the terms 

 north or south Galactic Latitude. 



The observations made in the northern hemisphere by 

 Sir W. Herschel, and subsequently continued in the 

 southern hemisphere by Sir J. Herschel, have supplied 

 data for determining the law of the distribution of the 

 stars according to their galactic latitude. The telescope 

 used in these observations had 18 inches aperture, 20 

 feet focal length, and a magnifying power of 180. It was 

 directed indiscriminately to every part of the celestial 

 sphere, visible in the latitude of the places of observa- 

 tion. The observations of Sir J. Herschel were made 

 during his residence at the Cape of Good Hope, in the 

 years 1834-8. About 2300 gages were obtained, dis- 

 tributed with tolerable impartiality over the southern 

 heavens. 



An analysis of the observations of Sir W. Herschel was 

 made by Professor Struve, with a view of determining 

 the mean, density of the stars in successive zones of galac- 

 tic latitude ; and a similar analysis has been made of the 



