252 Trees, Stars, and Birds 



Even when viewed with a large telescope it does not 

 show plainly any markings such as are seen on Mars, 

 Jupiter, or Saturn. 



Satellites of Uranus. A few years after his dis- 

 covery of Uranus, Herschel found that it had two 

 satellites. Later two others were discovered. All of 

 them are small. They revolve around Uranus in dif- 

 ferent periods, the one most distant from the planet 

 requiring nearly 13^- days to complete a revolution, 

 while the nearest satellite goes around 5 times in less 

 than 13 days. 



NEPTUNE 



Neptune, the most remote of the planets, is about 

 60 times as large as the earth. If it were self-luminous 

 like the stars, it would appear brighter than any of them, 

 for it is very much nearer. But as it is seen only by 

 reflected sunlight, and is so far away, it is visible only 

 with a telescope or, possibly, with good opera glasses. 

 No one had noticed it until 1846, when it was found 

 within half an hour after the astronomers began to look 

 for it. Why did they look for such a body and how did 

 they know where to look? If a ball were lost in another 

 state and you had no clew whatever as to what part of 

 the state it was in, you surely would not undertake to 

 find it. 



It was the behavior of Uranus that set the astronomers 

 to hunting for a new planet. Uranus was found to 

 move in an irregular manner that could not be ex- 

 plained without taking into account the attraction of 

 some body which had not been seen. A French as- 

 tronomer, Leverrier, and a young Englishman named 



