A WHEWELLITE ESSAY ON MARS. 153 



regions the moisture-laden air. In this way probably 

 the polar snows of the planet are recruited. The polar 

 regions must, in fact, act the part of veritable con- 

 densers, if the circulation of the Martian atmosphere is 

 as brisk as it may well be believed to be. There must 

 in that case be a continual gathering of fresh snows at 

 the poles, and a continual downward motion of the 

 glaciers thus formed, accompanied necessarily by a very 

 active abrasion and erosion of the planet's polar regions. 

 It seems by no means improbable, moreover, that as 

 Mr. Mattieu Williams opines, there may be from time 

 to time great catastrophes in these polar regions, pro- 

 duced by the toppling over or the rapid downward 

 sliding of great glacial masses. For many considerations 

 suggest that there must be an activity in the process 

 of snow-gathering at the Martian poles altogether un- 

 like anything known on our earth. It is noteworthy 

 also that according to reliable observations changes 

 have taken place in the aspect of the Martian snow- 

 caps which imply catastrophes affecting ice-masses of 

 enormous dimensions. Assuredly none of the changes 

 taking place in our own polar regions could be dis- 

 cerned at so great a distance as separates us from Mars, 

 save only the gradual increase and diminution of the 

 extent of the snow-covering as winter or summer is in 

 progress. An ice-mass as large as Spitzbergen or Nova 

 Zernbla would not be separately discernible from so 

 great a distance, and therefore the complete destruction 

 of such a mass by collision or downfall would be quite 

 imperceptible at that distance, though it would be an 



