LIFE IN SPACE AND TIME ip 



planet. They show, too, conspicuous differences of intensity, 

 and depth of color, within their own areas, which could 

 hardly occur in water unless it was very shallow. Most 

 noteworthy of all, they exhibit marked seasonal changes. 

 Even the principal markings, though of fairly permanent 

 form and position, vary greatly in intensity, being at times 

 conspicuous, and again almost invisible. 



Speaking broadly, they are most prominent in the spring 

 of the hemisphere in which they lie, and tend to fade out 

 in the autumn and winter, at which season the color some- 

 times changes from greenish to yellow or brown. These 

 changes, though repeating themselves roughly in successive 

 seasons, show considerable irregularity. 



Crossing the lighter regions between the dark areas, and 

 in some cases the latter themselves, are the finer markings 

 known as the canals, discovered by Schiaparelli in 1877. 

 No doubt remains of the reality of such markings, for many 

 of them have been photographed time and again. The photo- 

 graphs show, too, that the canals are of the same general 

 color as the dark areas, for, like the latter, they come out 

 strongly on photographs taken with red light, and are 

 inconspicuous with* blue or violet. It is well established, 

 too, that they show seasonal changes in visibility which 

 run parallel to those of the dark areas. 



On one further point all observers of the canals are 

 agreed; they are difficult and elusive, and can be well seen 

 only at those favorable times when the incessant turbulence 

 of the Earth's atmosphere, which produces the confusion 

 of the telescopic image known as "bad seeing," quiets 

 down for a few moments and permits a relatively clear 

 view of the planet. Concerning their appearance, when 

 best seen, experienced observers are in extraordinary 

 disagreement. Some, like the late Percival Lowell, drew 

 them as fine sharp lines, following great circles on the 

 sphere for hundreds of miles, meeting by threes, fours, or 

 more, at sharply defined points, and covering the whole 

 planet with a geometrical network. Others, such as Barnard, 

 described instead a complex mass of fine detail, appearing 

 as if it "had been painted with a very poor brush, producing 

 a shredded or streaky and wispy efi'ect," but failed altogether 



