88 Life Conditions in other Worlds. 



rather more than twenty-four hours and a half does not differ 

 enough from the same terrestrial period to exert any special 

 action upon living beings ; but the year contains 669f- rotations, 

 and thus the seasons are much longer than our own. 



The polar snow and ice masses visible in Mars afford 

 an analogy to our earth, which is strengthened as the 

 observer sees them, diminishing or disappearing as the Martial 

 summer comes on. That Mars has an atmosphere is obvious 

 from inspection, and it forms clouds and deposits moisture like 

 our own. How far it differs from ours we do not know ; but 

 the observations of Mr. Huggins, detailed in .our last number, 

 show that it contains substances which absorb a good many 

 of the more refrangible rays, and thus cause the planet to 

 assume a red tint. The extent of the polar snow in winter, as 

 compared with summer, shows that a considerable portion of 

 the planet undergoes great changes of temperature correspond- 

 ing with the seasons ; and from the general disposition of land 

 and water — the reverse of what obtains with us — the general 

 climate must be continental, as contra- distinguished from 

 insular.* It was thought at one time that the atmosphere of 

 Mars extended to a considerable distance from the body of 

 the planet ; but the observations of Sir William Herschel, who 

 watched minute stars close to the disc, negative this idea. 

 The weight with which ■ an atmosphere presses upon a globe 

 depends upon its density and its height, and upon the force 

 with which gravitation attracts a given mass. In the case of 

 Mars, the atmospheric pressure or density probably does not 

 differ so much from our own as to render that planet unfit to 

 be the abode of creatures bearing some resemblance to those 

 we are acquainted with. 



Mr. Huggins finds evidence for supposing that both Jupiter 

 and Saturn have in their atmospheres the gases that occur in 

 our own, though with what admixture does not yet appear. 

 Venus proved about as intractable under the spectroscope as 

 she does under the telescope. Her clouds reflected solar light, 

 and did not permit any sufficient reflection from the body of 

 the planet of rays that had traversed her whole atmosphere, 

 and been affected by the materials it contains. 



The amount of resemblance traced between the atmospheres 

 of Jupiter, Saturn, and that of the earth, increases the proba- 

 bility of their inhabitation by beings performing the functions of 

 respiration. The enormous size of the former planet, which is 

 more than eleven times the diameter of the • earth, gives it a 



* Astronomers usually consider the dark portions seas, and the bright ones 

 land. The dark parts exhibit as much prominence as could be expected from the 

 circumstance of our viewing them through an atmosphere laden with variable 

 clouds. See Mr. Webb's valuable paper, vol. iy., p. 182. 



