256 ELEMENTS OF GENERAL SCIENCE 



the polar cap gradually disappears. The fact that the snow 

 disappears from the poles of Mars as the spring approaches 

 means in the first place that it is probably thin, and hi the 

 second place that the atmosphere above it is probably dry 

 so that the process of evaporation takes place. 



259. The "canals" upon Mars. Interest in Mars received a 

 great stimulus in 1877 by the discovery of markings upon it 

 by an Italian astronomer, Schiaparelli. The markings which he 

 observed appeared to be very long and straight and narrow. 

 He called them canali, which unfortunately was translated into 

 English as canals. This led some people to the conclusion 

 that upon the surface of Mars there is an immense network 

 of irrigation ditches, which, of course, could only have been 

 made if the planet were inhabited by highly intelligent beings. 



The American astronomer Lowell was also convinced of 

 the reality of the markings. He said that the markings are 

 about 20 miles wide and from a few hundred miles to 3500 

 miles long. He thought they are not canals, but streaks of 

 vegetation which grow along the banks of irrigating ditches. 

 He suggested that along the middle of one of the so-called 

 canals there is an irrigation ditch or canal with smaller 

 ditches leading off to the sides, which together irrigate a 

 tract of country from 20 to 50 miles in width and as long 

 as the canal. This interpretation also implies the existence 

 of highly intelligent creatures on the planet. 



The conclusions of Lowell have not obtained very wide 

 acceptance among astronomers because, in the first plae, 

 the observational data are uncertain, and in the second place, 

 the interpretation of them involves serious difficulties which 

 as yet have not been removed. There are upon Mars con- 

 ditions of temperature and moisture which would seem to 

 us to make intelligent life impossible. 



260. Jupiter. Jupiter is the greatest of all the planets and 

 is in volume more than one thousand times as large as the 

 earth. It has no fixed markings upon its surface, but there 



