138 THE BORDERLAND OF SCIENCE. 



heated body. For according to the most generally 

 received explanation of the original intense heat of the 

 planet, such heat had its origin in the rush of matter 

 drawn in by the attractive might of the aggregation 

 which was, so to speak, the embryon of the planet. 

 Thus the smaller planets, which must necessarily have 

 had less attractive energy than the larger, would 

 impart a less velocity to the inrushing matter, and 

 therefore would be less intensely heated. On all accounts 

 it would follow that Mars is, at the present time, a 

 much colder body than the earth. 



Our sole resource, therefore, if we are to adopt the 

 theory that the climate of Mars resembles that of the 

 earth, is to assume that there is some peculiarity in his 

 atmosphere by which it is enabled to retain a larger 

 proportion of the heat received from the sun than 

 happens in the case of our own atmosphere. If we 

 are further to assume that the constitution of the 

 atmosphere resembles that of our air and no other 

 assumption is compatible with the belief that creatures 

 such as we are familiar with can exist in Mars we 

 must assume that the Martial atmosphere is much 

 more dense than our own. We need not enter here 

 into the considerations on which this inference is based. 

 Let it suffice to remark that there is a steady decrease 

 of warmth with elevation in all parts of the earth, this 

 decrease being unquestionably due to the greater 

 tenuity of the air in high regions. And it is certain 

 that if the density of the air were in any way increased, 

 there would be a corresponding increase of warmth. 



