LIFE IN MAES. 1 15 



to the conclusion that it is well fitted to be the abode 

 of life. We can trace, indeed, the progress of such 

 changes as we may conceive that the inhabitants of 

 Venus or of Mercury must recognise in the case of our 

 own earth. The progress of summer and winter in the 

 northern and southern halves of the planet, the effects 

 due to the progress of the Martial day, from sunrise to 

 sunset nay, even hourly changes, corresponding to 

 those which take place in our own skies, as clouds 

 gather over our continents, or fall in rain, or are dissi- 

 pated by solar heat: such signs as these that Mars 

 is a world like ours can be recognised most clearly 

 by all who care to study the planet with a telescope 

 of adequate power. 



As regards the atmosphere of Mars, by the way, the 

 earliest telescopic observers fell into a somewhat strange 

 mistake. For, noticing that stars seemed to disappear 

 from view at some considerable distance from the 

 planet, they assigned to the Martial atmosphere a 

 depth of many hundreds of miles, we care not to say 

 how many. More careful observation, however, showed 

 that the phenonemon upon which so much stress had 

 been laid was merely optical. Sir J. South and other 

 observers, carefully studying the planet with telescopes 

 of modern construction, have been able to prove 

 abundantly that the atmosphere of Mars has no such 

 abnormal extension as Cassini and others of the earlier 

 telescopists had imagined. 



The early observations made on the polar snows of 

 Mars were more trustworthy. Maraldi found that at 



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