CHAPTER I. 



RECENT ADDITIONS TO OUR KNOWLEDGE OF THE 

 PLANETARY SYSTEM. 



SECTION I. 



THE DISCOVERY OF THE PLANET NEPTUNE. 



THE discovery of the planet Neptune took place un- 

 der circumstances most extraordinary. The existence 

 of the planet was predicted, its path in the heavens was 

 assigned, its mass was calculated, from considerations 

 purely theoretical. The astronomer was told where to 

 direct his telescope, and he would see a planet hitherto 

 unobserved. The telescope was pointed, and there the 

 planet was found. In the whole history of astronomy 

 we can find few things equally wonderful. This dis- 

 covery resulted from the study of the motions of the 

 planet Uranus. 



Uranus was first discovered to be a planet in 1781, 

 but it had been repeatedly observed before by different 

 astronomers, and mistaken for a fixed star. Nineteen 

 observations of this description are on record, one of 

 them dating as far back as 1690, In 1821, M. Bouvard, 

 :>f Paris, published a set of tables for computing the 



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