A WHEWELLITE ESSAY ON MARS. 



If Mars then not only receives day by day a much 

 smaller supply of light and heat than our earth, but 

 has been similarly circumstanced during all those past 

 ages which supply the facts studied by geologists, what 

 opinion must we form as to his present fitness to be the 

 abode of creatures like those which exist upon our earth ? 

 It appears to us that there can be but one answer to 

 this question. Our only doubt must depend on our ac- 

 ceptance of the opinion on which the question is based. 

 If in any way the supply of heat has been increased, 

 or which amounts to the same thing if a greater 

 portion of the direct supply has been stored up, then, and 

 then only can we regard Mars as a suitable abode for 

 living creatures like those on the earth. For we may 

 dismiss the supposition that the inherent heat of Mars's 

 globe is such as to compensate for a deficiency in the 

 supply of solar heat. So far is this from being at all 

 probable, that on the contrary an additional difficulty 

 is introduced by the consideration that in all reason- 

 able likelihood Mars must have parted with a very 

 much greater proportion of his inherent heat than our 

 earth. His globe is very much smaller than that of 

 the earth, and the total quantity of matter contained 

 in it is little more than one-ninth of the matter con- 

 tained in the earth's globe. Now, it is known that of 

 two bodies equally heated, the smaller cools more 

 rapidly than the larger. And certainly we have no 

 reason to believe that at any epoch Mars was hotter 

 than the earth at the same epoch. We should 

 infer, indeed, that Mars was always much the less 



