MARS, BY THE LATEST OBSERVATIONS. 191 



We speak of plants on Mars, of the snows at its poles, of its seas, 

 atmosphere, and clouds, as though we had seen them. Are we justi- 

 fied in tracing all these analogies ? In fact, we see only blotches of red, 

 green, and white, upon the little disk of the planet ; but, is the red 

 terra firma ; the green, water ; or the white, snow ? Yes, we are now 

 justified in saying that they are. For two centuries astronomers were 

 in error with regard to spots on the moon, which were taken for seas, 

 whereas they are motionless deserts, desolate regions where no breeze 

 ever stirs. But it is otherwise as regards the spots on Mars. 



The unvarying aspect of the moon never exhibits the slightest 

 cloud upon its surface, nor do the occultations of stars by its disk re- 

 veal even the slightest traces of an atmosphere. Contrariwise, the 

 aspect of Mars is ever varying. White spots move about over its disk, 

 very often modifying its apparent configuration. These spots can be 

 nothing else but clouds. The white spots at its poles increase or di- 

 minish with the seasons, exactly like the circumpolar ice of earth, 

 which, for an observer on Yenus, would have the same aspect and the 

 same variations as the polar spots of Mars have for us. Hence we 

 conclude that these Martial white polar spots are masses of frozen 

 water. Each hemisphere of Mars is harder to observe during its win- 

 ter than during its summer, being often covered with clouds over its 

 greater part. This would be precisely the aspect of the earth if ob- 

 served from "Venus. But what causes these clouds over Mars ? Plainly 

 nothing else but the evaporation of water. As for the ice, that is the 

 same water frozen. But is the water there the same as here ? Down 

 to a few years ago, this question remained unanswered, but now it ad- 

 mits of a reply, thanks to the spectroscope, and the observations espe- 

 cially of Mr. Huggins. 



The planets reflect the light they receive from the sun ; on examin- 

 ing their spectra, we find the solar spectrum as though it had been re- 

 flected from a mirror. If we direct the spectroscope on Mars, we get, 

 first of all, an image perfectly identical with that produced by the 

 central star of our system. But, by the employment of more exact 

 methods, Mr. Huggins found, during the last opposition of the planet, 

 that the spectrum of Mars is crossed, in its orange portion, by a group 

 of black lines coincident with the lines which appear in the solar spec- 

 trum at sunset when the sun's light passes through the denser strata 

 of our atmosphere. Now, are these tell-tale rays produced by our at- 

 mosphere ? To decide this question, the spectroscope was turned on 

 the moon, which was at the time nearer the horizon than Mars. If the 

 lines in question were produced by our atmosphere, they must have 

 appeared in the lunar as well as in the Martial spectrum, and with 

 greater intensity in the former. Yet they were not to be seen at all 

 in the lunar spectrum ; and hence it is plain that they are owing to the 

 atmosphere of Mars. 



The atmosphere of that planet, therefore, adds these special char- 



