ISrOTES ON MAES, 161 



globes is sufficiently potent to retiiiu even un atmosphere of this subtle 

 element. * * * 



The discussion we have just g-iven will prepare us to believe that a 

 planet with the size and mass of Mars may be expected to be encom- 

 passed with an atmosphere. Our telescopic observations completely 

 bear this out. It is perfect!}" certain that there is a certain shell of 

 gaseous material investing Mars. This is shown in various waj^s. We 

 note the gradual obscuration of objects on the planet as they approach 

 the edge of the disk, where they are necessarily viewed through a 

 greatly increased thickness of Martian atmosphere. We also observe 

 the clearness with which objects are exhibited at the center of the disk 

 of Mars, and though this may be in some measure due to the absence 

 of distortion from the effects of foreshortening, it undoubtedly arises 

 to some extent from the fact that objects in this position are viewed 

 through a comparativel}' small thickness of the atmosphere enveloping 

 the planet. Clouds are also sometimes seen apparently floating in the 

 upper region of Mars. This, of course, is possible only on the suppo- 

 sition that there must be an atmosphere which formed the vehicle by 

 which clouds were borne along. It is, however, quite obvious that the 

 extent of the Martian atmosphere must be quite insignificant when 

 compared with that by which our earth is enveloped. It is a rare cir- 

 cumstance for any of the main topographical features, such as the out- 

 lines of its so-called continents or the coasts of its so-called seas, to be 

 obscured by clouds to an extent which is appreciable except by very 

 refined observations. Quite otherwise would l^e the appearance which 

 our globe would present to any observer who would view it, say, from 

 Mars or from some other external world at the same distance. The 

 greater part of our globe would seem swathed with vast clouds, through 

 which only occasional peeps could be had at the actual configuration 

 of its surface. I dare say a Martian astronomer who had an observa- 

 tory with sufficient!}" good optical appliances and who possessed suffi- 

 cient patience might, in the course of time, b}^ availing himself of 

 every opportunity, gradually limn out a chart of the earth which would 

 in some degree represent that with which we are familiar in our atlases. 

 It would, however, be a ver}'^ tedious matter, owing to the interrup- 

 tions to the survey caused by the obscurities in our atmosphere. The 

 distant astronomer would never l)e able to comprehend the whole of 

 our earth's features in a bird's-eye glance, as we are able to do with 

 those features on that hemisphere of Mars which happens to be turned 

 toward us on a clear night. 



As to what the composition of the atmosphere on Mars may be we 

 can say but little. In so far as the sustenance of life is concerned, the 

 main question, of course, turns on the presence or the absence of oxy- 

 gen. It may be pertinent to this inquir}" to remark here that a globe 



SM 1900 11 



