THE EARTH AS A PART OF THE SOLAR SYSTEM 529 



Some astronomers argue that this arrangement could not 

 happen by chance but that there must be intelligent beings 

 there. Their explanation is that these are belts of vegeta- 

 tion along irrigation canals ; that water is scarce, and that as 

 the snow melts from about the poles in the summer, the 

 water is carried by those canals to other parts of the planet 

 to be used for irrigation. There are changes in the appear- 

 ance, as though at one season of the year snow accumulated 

 around the poles, and then melted during another season. 

 While it cannot be considered proved that Mars is inhab- 

 ited, it certainly is a very entertaining theory. Wells, the 



FIG. 211. The planet Saturn in 1894, as seen with the telescope. 



English novelist, has written a very interesting book called 

 The War of the Worlds, in which he supposes that the in- 

 habitants of Mars come to the earth and wage warfare 

 against the inhabitants here, but are finally killed by 

 bacteria. 



Telescope. Many of the facts known about the heavenly 

 bodies have been learned through the use of the telescope. 

 This is an instrument for looking at distant objects and 

 making them appear larger than they do to the naked eye. 

 It is composed of two convex lenses mounted at the two ends 

 of a tube. The one pointed toward the object is called the 

 objective; the one at the other end, the eyepiece. The 



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