96 A CENTURY'S PROGRESS IN ASTRONOMY. 



previous observations, and reaffirmed the presence 

 of water- vapour in the Martian atmosphere. 



During the opposition of 1830, Madler under- 

 took an extensive search for a Martian satellite, 

 but was unsuccessful. In 1862 the search was 

 resumed by Heinrich Louis U Arrest (1822-1875), 

 the famous German observer, who was also un- 

 successful. Accordingly the red planet was re- 

 ferred to by Tennyson as the "moonless Mars." 

 In 1877 the search was taken up by Asaph 

 Hall, the self-made American astronomer, born 

 at Goshen, Connecticut, in 1829, and employed 

 from 1862 to 1891 at the Naval Observatory, 

 Washington. During the famous opposition of 

 August 1877, favoured by the great 26 -inch 

 refractor, he succeeded in discovering two very 

 small satellites of Mars, to which he gave the 

 names of Phobos and Deimos. He determined 

 the time of revolution of Phobos at 7 hours 

 39 minutes, and that of Deimos at 30 hours 

 17 minutes, Phobos revolving round Mars more 

 than three times for one rotation of the planet 

 on its axis. These two satellites are very small, 

 not more than thirty miles in diameter. After 

 Hall's successful search, photographs were ex- 

 posed at the Paris Observatory for other Martian 

 satellites, but none was discovered. No further 

 moons have been found belonging to the red 



