Celestial Bodies 149 
past and will certainly recur in the future. Mankind has al- 
ready weathered several ice ages, and will probably see some 
more. 
IS THERE LIFE ON MARS? 
Next in line after the Earth is the planet Mars, somewhat 
smaller than the Earth but large enough to show some rather 
definite surface features under satisfactory conditions. A 
good though not large telescope is necessary to view the 
features of Mars. Most striking of all the features is the polar 
ice cap, a white spot on the planet’s visible pole which 
changes its size and shape with the Martian seasons, becom- 
_ing large in the winter and small in the summer. Besides the 
polar ice cap there are large areas of dusky dark green color 
which also Wary in size, shape and intensity as the seasons 
change. Some astronomers are inclined to attribute these 
spots to large forests or growths of some kind of vegetation, 
while others, who refuse to admit any kind of life is possible 
on Mars, postulate hygroscopic (moisture-absorbing) min- 
erals of one sort or another. Thirdly, we should mention the 
“canals” of Mars, the most fascinating and most debatable 
feature of the planet. Many astronomers of good repute have 
insisted that they have seen long, dark lines on the surface 
of Mars which have been given the name canals, although 
this term was never meant to signify that they were actual 
water-filled canals. Other equally good astronomers, with 
eyes just as keen, have tried to see the same canals through ~ 
the same telescope during the same night and have positively 
been unable to see any such markings. Photography is unable 
to settle the issue. Most photographs have shown no canals, 
but some show faint blurred markings which suggest mark- 
