142 THE BORDERLAND OF SCIENCE. 



of the Martial atmosphere that sufficient water-vapour 

 can never be raised into that air to produce a perma- 

 nent snow-envelope by precipitation. This view (on 

 which we shall presently touch again) of course accords 

 well with the a priori opinion respecting the Martian 

 atmosphere referred to above. And therefore it seems 

 to us manifestly the most probable and satisfactory 

 course to assume that the Martian atmosphere bears 

 about the same relation to ours in quantity which the 

 mass of Mars bears to that of the earth. On this 

 assumption it is easily shown that the atmospheric 

 pressure on Mars corresponds to about four and a half 

 inches of the mercurial barometer. We may take five 

 inches as a fair probable estimate of the height of 

 Martian barometric tubes, supposing there are any 

 reasoning creatures on Mars who have made the same 

 discovery as our terrestrial Torricelli. 



At this stage it may be interesting to inquire whether 

 the mere tenuity of the Martian air, on our assumption, 

 would be a fatal objection to the theory that creatures 

 like men can live on the planet. Could any man, for 

 instance, exist for any length of time in an atmosphere 

 corresponding in pressure to only four or five inches of 

 the common barometer? or could any race of men, 

 after a gradual process of acclimatisation, become 

 enabled not merely to live in such an atmosphere but 

 to thrive as a race, to undergo ordinary labours, to 

 travel without being easily exhausted, and, if need were, 

 to defend themselves against their enemies or from 

 sudden natural dangers ? 



