NOTES ON MAKS. 163 



As we have already said, Mars is at present at a distance of 35,000,000 

 miles, and if we look at it through a telescope of such a power as we 

 have described, the apparent distance is reduced to one-thousandth 

 part. In other words, all that the best telescope can possibly do is to 

 exhibit the planet to us as it would be seen by the unaided eye if it 

 were brought into a distance of 35,000 miles. This will demonstrate 

 that even our greatest telescopes can not be expected to enable us to 

 answer the questions that are so often asked about our neighboring 

 globe. What could we learn of Europe if we have only a bird's-eye 

 view of it from a height of 35,000 miles; that is to say, from a height 

 which was a dozen times as far as from the shores of Europe to Amer- 

 ica? The broad outlines of the coast might of course be seen by the 

 contrast of the color of a continent and the color of the ocean. Pos- 

 sibly a great mountain mass like the Alps would be sufficiently notice- 

 able to permit some conjecture as to its character to be formed. But 

 it is obvious that it would be hopeless to expect to see details. The 

 smallest object that would be discernible on Mars must be as large as 

 London. It would not be possible to see a point so small as would 

 either Liverpool or Manchester be if they were on that point. There 

 is, no doubt, a remarkable contrast between the dark colors of certain 

 parts of Mars and the ruddy colors of other parts. It would, how- 

 ever, be going rather far to assert that the former must be oceans of 

 water and the latter continents of land. This may indeed be the case, 

 and most astronomers, I believe, think that it is the case, but it cer- 

 tainly has not yet been proved to be so. 



Undoubtedly the most striking piece of evidence that can be adduced 

 in favor of the supposition that there is water on Mars is derived from 

 the "snowy " poles on the planet. The appearance of the poles of Mars 

 with their white caps is one of the most curious features of the solar 

 system. The resemblance to the structure of our own polar regions 

 is extremely instructive. It is evident that there must be some white 

 material which from time to time gathers in mighty volume round the 

 north and south poles of the planet. 



It is also to be noticed that this accumulation is not permanent. The 

 amount of it waxes and wanes in correspondence with the variations 

 of the seasons on Mars. It increases during Mars's Avinter, and it 

 declines again during Mars's summer. In this respect the white 

 regions, whatever they may be composed of, present a noteworthy 

 contrast to the majority of the other features on the planet. The 

 latter offer no periodic changes to our notice; they are evidently com- 

 paratively permanent marks, not to any appreciable extent subject to 

 seasonal variations. When we reflect that this white material is some- 

 thing which grows and then disappears according to a regular period, 

 it is impossible to resist the supposition that it must be snow, or pos- 

 sibly the congealed form of some liquid other than water, which dur- 

 ing Mars's summer is restored to a fluid state. There can hardly be 



