A WHEWELLITE ESSAY ON MARS. 147 



{15,000 feet), it will be admitted that man can become 

 habituated to the rarefied air of the highest mountains.' 

 These places are, however, tropical, and it is manifest 

 that cold plays an important part in producing the 

 unpleasant sensations which are experienced in elevated 

 regions. Since in Mars (according to our present 

 assumption) we have not only a much greater atmo- 

 spheric rarity than at the highest peak of the Hima- 

 layas, but also a much greater degree of cold than at 

 such a height even in high latitudes, it is manifest that 

 absolute uninhabitability by human beings must result. 

 Nay, since no living things except microscopic animal- 

 cules exist above certain elevations, or when a certain 

 degree of cold is experienced, it remains clear that 

 Mars cannot possibly be inhabited by creatures resem- 

 bling any of the higher forms of living beings with 

 which we are familiar on earth. ' Beyond the last stage 

 of vegetation, beyond the extreme region attained by 

 the insect and mammifers, all becomes silent and un- 

 inhabited,' says Flammarion,' 'though the air is still 

 full of microscopic animalcules which the wind raises 

 up like dust and which are disseminated to an unknown 

 height.' 



But the reader may be led to ask, at this stage, what 

 is actually taking place in Mars when our astronomers 

 perceive signs as of clouds forming and dissolving, of 

 morning and evening mists, and other phenomena not 

 compatible, it should seem, with the idea of extreme cold. 

 Nay, it is to be remembered that even the presence of 

 ice and snow implies the action of heat. ' Cold alone,' 



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