ASTRONOMY 



till the nineteenth century was well advanced, 

 but out of the close union which has now been 

 established has arisen what is almost a distinct 

 branch of Astronomy bearing the name of Astro- 

 physics. 



It is, however, unnecessary to enlarge upon 

 the general relations existing between these various 

 sciences, for the special instances with which we 

 shall be concerned will illustrate them in a sufficient 

 manner. 



Up to the beginning of the nineteenth century 

 the interest of astronomers was centred chiefly 

 upon our nearest neighbours in space, that limited 

 group of bodies comprising the sun, moon, planets, 

 and comets which form the Solar System. About 

 the stars very little was known. It was clear that 

 their distances from our system were very great 

 even in comparison with the distance of the 

 farthest known planet. Apart from differences in 

 brightness and colour they exhibited no striking 

 individual characteristics. They were mere points 

 of light, and as they appeared to maintain their 

 distances from one another unchanged, their chief 

 use was to serve as fixed marks of reference to 

 which the motions of the members of the Solar 

 System might be referred. In addition to the 

 stars, a limited number of dim cloudy masses, to 

 which the name of nebulas was given, were found 

 to exist in certain parts of the heavens, and their 



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