

A MIGHTY SEA- WAVE. 197 



lower side of the polar spot. " In the early part of the 

 evening," he says, " the small bright spot seemed to be partly 

 buried in the large one. After the lapse of an hour or more 

 my attention was again directed to the planet, when I was 

 astonished to find a manifest change in the position of the 

 small bright spot. It had apparently separated from the 

 large spot, and the edges alone of the two were now in con- 

 tact, whereas when first seen they overlapped by an amount 

 quite equal to one-third of the diameter of the small one. 

 This, however, was merely an optical phenomenon, for on 

 the next evening the spots went through the same apparent 

 changes as the planet went through the corresponding part 

 of its rotation. But it showed the spots to be real ice 

 masses. The strange part of the story is that in the course 

 of a few days the smaller spot, which must have been a mass 

 of snow and ice as large as Novaia Zemlia, gradually dis- 

 appeared. Probably some great shock had separated an 

 enormous field of ice from the polar snows, and it had 

 eventually been broken up and its fragments carried away 

 from the Arctic regions by currents in the Martian oceans. It 

 appears to me that the study of our own earth, and of the 

 changes and occasional convulsions which affect its surface, 

 gives to the observation of such phenomena as I have just 

 described a new interest Or rather, perhaps, it is not too 

 much to say that the telescopic observations of the planets 

 derive their only real interest from such considerations. 



I may note in conclusion, that while on the one hand 

 we cannot doubt that the earth is slowly parting with its 

 internal heat, and thus losing century by century a portion 

 of its Vulcanian energy, such phenomena as the Peruvian 

 earthquakes show that the loss of energy is taking place so 

 slowly that the diminution during many ages is almost imper- 

 ceptible. As I have elsewhere remarked, " When we see 

 that while mountain ranges were being upheaved or valleys 

 depressed to their present position, race after race and type 

 after type lived out on the earth the long lives which belong 

 to races and to types, we recognize the great work which the 



