for the year 1878. xxiii 



refractors and reflectors unfavourable to the latter ; but in 

 this I do not acquiesce, for, during our search, stars, far 

 more minute than the satellites, were traced close up to the 

 edge of Mars, and had we known of or suspected the 

 existence of satellites in August or September, and had 

 favourable weather, I feel confident we should have found 

 them and kept them in tow ; as it was, our watch com- 

 menced only late in October, in broken weather. " Moon- 

 lit " (not " moonless ") Mars is undoubtedly accompanied 

 by two satellites at least, and the observers at Washington 

 suspect the existence of a third. The most remarkable 

 feature in connection with these bodies is their exceeding 

 smallness, and their nearness to the primary. The inner 

 satellite cannot be 4000 miles from the surface of Mars, 

 or less than one-sixtieth of our moon's distance from 

 us ; and should there be any Martial astronomers 

 with good telescopes, they could not be long in doubt 

 as to whether their moons are inhabited or not. The 

 estimated diameter of the smallest of these bodies is 

 only about seven miles, giving a surface of 154 square 

 miles, equal to a few Australian sheep-runs. The larger and 

 inner satellite is probably about thirty miles in diameter, 

 and with a superficial area of 2826 square miles. The 

 minuteness of these bodies renders it highly improbable 

 that they will again be seen until the next near approach of 

 Mars to the earth, about fifteen years hence. Our know- 

 ledge of the constitution of the sun has again been further 

 supplemented by help of the spectroscope. The spec- 

 trum of hydrogen gas, in the bright line form in the chromo- 

 sphere and reversed in the photosphere, has long since been 

 recognised, but the presence of no other of our known gases 

 had as yet been ascertained. Professor Draper, however, 

 about July last year obtained photographs showing bright 

 lines of oxygen at the extreme blue end of the spectrum 



