.50 The Outline of Science 



fessor W. II. Pickering, another high authority, thinks that the 

 lines an- lonjr. narrow marshes fed by moist winds from the poles. 

 Then- are certainly white polar eaps on Mars. They seem to 

 melt in the spring, and the dark fringe round them grows broader. 



Other astronomers, however, say that they find no trace of 

 water-vapour in the atmosphere of Mars, and they think that the 

 polar eaps may he simply thin sheets of hoar-frost or frozen gas. 

 They point out that, as the atmosphere of Mars is certainly 

 scanty, and the distance from the sun is so great, it may be too 

 cold for the fluid water to exist on the planet. 



If one asks why our wonderful instruments cannot settle these 

 points, one must be reminded that Mars is never nearer than 

 .'{4,000,000 miles from the earth, and only approaches to this dis- 

 tance once in fifteen or seventeen years. The image of Mars on 

 the photographic negative taken in a big telescope is very small. 

 Astronomers rely to a great extent on the eye, which is more sen- 

 sitive than the photographic plate. But it is easy to have differ- 

 ences of opinion as to what the eye sees, and so there is a good deal 

 of controversy. 



In August, 1924, the planet will again be well placed for 

 observation, and we may learn more about it. Already a few 

 of the much-disputed lines, which people wrongly call "canals," 

 have been traced on photographs. Astronomers who are sceptical 

 about life on Mars are often not fully aware of the extraordinary 

 adaptability of life. There was a time when the climate of the 

 whole earth, from pole to pole, was semi-tropical for millions of 

 years. \o animal could then endure the least cold, yet now we 

 have plenty of Arctic plants and animals. If the cold came slowly 

 on Mars, as we have reason to suppose, the population could be 

 gradually adapted to it. On the whole, it is possible that there 

 is advanced life on Mars, and it is not impossible, in spite of the 

 y great difficulties of a code of communication, that our "elder 

 brothers" may yet flash across space the solution of many of our 

 problems. 



