I68 IN STARRY REALMS. 



rather strange that the remaining planets Mercury, 

 Venus, and Mars should be entirely unprovided with 

 whatever benefits the possession of attendant moons is 

 competent to bestow. So far as Mercury and Venus are 

 concerned, it may, indeed, be contended that the pre- 

 sumption that they ought to have moons had but little 

 substantial basis. It was obvious that the outer planets 

 had, on the whole, more satellites than the inner planets, 

 and as the earth had only one moon, while Venus and 

 Mercury both revolved in orbits inside that of the earth, it 

 was obvious that there was but slender ground for expect- 

 ing that Mercury or Venus should be found provided with 

 attendant orbs. But the case of Mars was different. As 

 Mars revolved in a path between that of the earth and 

 Jupiter, and as the earth had one moon and Jupiter had 

 four, it could be plausibly contended that Mars ought to 

 have at least a couple. But before the year 1877 this 

 conjecture was entirely devoid of any telescopic corrobora- 

 tion, and the " moonless Mars " was the phrase in which 

 one of the five great planets of antiquity was somewhat 

 contemptuously spoken of. 



While the British Association was holding its annual 

 session at Plymouth, in 1877, a telegram arrived from 

 the United States, stating that Professor Asaph Hall had 

 achieved the superb feat of discovering two satellites 

 to Mars, and had shown that these satellites were 

 objects of the utmost interest. I well remember the 

 enthusiasm which this announcement produced among 

 the philosophers then assembled at Plymouth. Of course 

 we were all impatient to learn the details of the process 

 of search, and the particulars of the observations. These 



