A WHEWELLITE ESSAY ON MARS. 131 



nomers to believe that in this planet conditions may 

 prevail which would render life possible for such 

 creatures as we are familiar with on earth. That essay 

 dealt, in fact, with the arguments which would have 

 been employed by Brewster in maintaining his position 

 against a Whewell of the present day. I propose 

 in the present essay to discuss certain considerations 

 which point in a different direction, and would certainly 

 not be left untouched by Whewell if he now lived, and 

 sought to maintain his position against the believers 

 in more worlds than one. 



It is a little hard perhaps, that an attack should be 

 made against the habitability of Mars ; for, though we 

 are in the habit of speaking somewhat confidently of 

 life in other worlds, it is, as a matter of fact, in Mars 

 alone that astronomers have hitherto recognised any 

 approach to those conditions which we regard as neces- 

 sary for the requirements of living beings. All that 

 is known about Mercury and Venus, tends to the con- 

 clusion that very few of the creatures existing on our 

 earth could live in either planet and assuredly man 

 is not among those creatures. It is not merely that in 

 both these planets the average daily supply of heat is 

 far greater than we could endure unscathed, but that 

 from the pose of these planets the slope of their axes 

 to the level of their path the supply of heat varies 

 greatly in amount, so that at one time there is much more 

 than even that average supply which we could, not bear, 

 and at another no heat is received at all for many days 

 in succession, or else a supply so small in quantity that 



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