1 9 1 2-1 9 1 3.] Some Astronomical Problems. 45 



of the planet. These fine markings called canals could not 

 be seen at all under these circumstances unless they were 

 about 200 miles in width. I think the idea of an artificial 

 origin for these markings may be dismissed without further 

 comment. 



Mars presents for our observation two polar caps which 

 increase and diminish in size according to seasonal changes, 

 but, curious to relate, at a much greater rate and more ex- 

 tensively than the polar caps of the earth. They exhibit 

 other peculiarities difficult to account for, being beyond our 

 experience here. With so much less heat received from the 

 sun, these remarkable variations in the polar caps of Mars 

 suggest that perhaps they are not composed of snow and ice, 

 as we know them, but of frozen gases. With an atmosphere 

 of the extreme tenuity in Mars which we have indicated, we 

 can hardly avoid the conclusion that even at the equator, in 

 the best of times, the cold must be excessive and much below 

 the freezing-point of water, if we bear in mind what was 

 said above in connection with the altitude of the snow-line 

 on the earth. Our earth, indeed, with all its advantages of 

 atmosphere and ocean, is frost-bitten at the poles. On the 

 highest mountains above the snow-line, where the air is very 

 rare and the cold intense, there is no sign of life, and yet 

 these extremely unfavourable conditions might be considered 

 advantageous when compared with the best that can be found 

 on Mars. I think we may be justified in concluding on 

 fairly reasonable grounds that Mars is not the seat of life. 

 In setting out on this speculative inquiry we may note, and 

 give due weight to the observation, that our nearest neighbour 

 in space, the moon, is without doubt lifeless. Though our 

 best telescopes bring us only within 200 miles of our satellite, 

 — and what can we expect to see at 200 miles range? — we 

 have no difficulty in coming to the conclusion that the moon 

 is an arid waste, absolutely lifeless. 



Having now reviewed the terrestrial planets, we may 

 glance at the major planets, — Jupiter, Saturn, Uranus, and 

 Neptune. No one dreams nowadays of inhabitants of any 

 kind for these worlds, vastly greater though they be compared 

 with our own. Their very small density, compared with their 

 great bulk, puts them out of court. In each case it is but the 



