of vegetal growth, [346], [347].

Secular change, in canals, [314].

Silurian era of the Earth, [134], [138], [140].

Sky, blotting out of, [14];

measure of extinction of, [16].

Sky, Martian, [89];

clear, [165].

Slipher, [101], [103].

Snow, [345];

limits of, on Earth and Mars, [108].