158 NOTES ON MARS. 



itself to our notice. But the significance of Mars is essentially derived 

 from those points of resemblance to the earth which are now engrossing 

 attention. Mars is clearlj" a possible world, presenting both remarkable 

 analogies and remarkable contrasts to our own world, and inducing us 

 to put forth our utmost endeavors to utilize so exceptional an occasion 

 as that presented in the close approach which it has now made. Let us 

 see what we have learned about this globe. 



In the first place, it should be noticed that Mars must be a small world 

 in comparison with our own. The width of this globe is only 4,200 

 miles, so that its volume is but the seventh part of that of the earth. 

 The weight of Mars is even less than what might have been expected 

 from his bulk. It would take nearly ten globes, each as heavy as Mars, 

 to form a weight equal to that of the earth. This fundamental differ- 

 ence in dimensions between Mars and our globe is intimately connected 

 with certain points of contrast which it offers to the earth. Of these 

 the most important i,s that which concerns the atmosphere. When we 

 consider the qualification of a globe as a possible abode for organic 

 beings, it is natural to inquire first into the presence or the absence of 

 an atmosphere. Seeing that our earth is enveloped b}^ so copious a 

 shell of air, it follows that the beings which dwell upon its surface 

 must be specially adapted to the conditions which the atmosphere im- 

 poses. Most, if not all, animals utilize this circumstance b}" obtaining 

 a proximate source of energj^ in the union of oxygen from the atmos- 

 phere with oxidizable materials within their bodies. In this respect 

 the atmosphere is of such fundamental importance that it is difficult 

 for us "to imagine what that type of life must be which would be fitted 

 for the inhabitants of an airless globe. In other respects, which are 

 hardly less important, the conditions of life are also dependent on the 

 fact that we live at the bottom of an ocean of air. It is the atmos- 

 phere which, to a large extent, mitigates the fierceness with which the 

 sun's ra3'S would beat down on the globe if it were devoid of such i^a'o- 

 tection. Again, at night, the atmospheric covering serves to screen 

 us from the cold that would otherwise be the consequence of unre- 

 stricted radiation from the earth to space. It is, therefore, obvious 

 that the absence of a copious atmosphere, though perhaps not abso- 

 lutely incompatible with life of some kind, must still necessitate tj^pes 

 of life of a wholl}" different character from those with which we are 

 familiar. In attempting, therefore, to form an estimate of the proba- 

 bility of life on another world it is of essential importance to consider 

 whether it possesses an atmosphere. * * *. 



Modern research has demonstrated that what we call a gas is in truth 

 a mighty host of molecules far too small to be perceptible by the most 

 powerful microscope. Each of these molecules is animated by a rapid 

 movement, which is only pursued for a short distance in one direction 

 before a rencontre takes place with some other molecule, in consequence 



