PICKERING. — LUNAR AND HAWAIIAN PHYSICAL I'KATIIU s COMPARED. 1 
Drawings of the Moon and planets show much finer detail than it is possible t< 
obtain by any photographs. Figure 37 is a drawing of Eratosthenes made thirty 
ht hours later in the lunation than the photograph. Few changes have taken 
o 
place in the meantime, and the three dark areas within the crater can be readily 
recognized. It will be noticed that numerous fine canals not at all visible in the 
photograph appear in the drawing. A much more detailed account of this crater will 
be found in the Annals of Harvard College Observatory, LIII, 75. 
Since different observers sometimes represent the same detail by different methods 
of shading, and since to some eyes fine' markings, like canals, appear of much less 
breadth than to others, it is very desirable where two drawings are to be compared, 
that they should both be, if possible, by the same observer. The sketch of Mars, 
Figure 38, was made by the writer when at the Lowell Observatory in Arizona. The 
similarity in appearance of the canals in these two figures, together with their varia- 
bility under similar conditions, leads one to believe that they are due to the ime 
cause, namely, vegetation. 
During the summer of 1904 the writer was able to spend eight weeks at the 
Lowe Observatory in southern California. A considerable portion of his time was 
devoted to a study of Eratosthenes. The interior was found to be seamed by 
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numerous fine cracks. Watching some of these cracks soon after the sun rose upon 
them, he was able to see them broaden out and change gradually into canals. It 
is his belief that the cracks gave out water vapor, which fertilized the vegetation 
along their sides and in their vicinity, and that it was the growth of this vegetation 
that produced the appearance of a canal. 
The canals of Mars are on a much larger scale than those of the Moon ; one of 
them indeed reaches the enormous length of 3500 miles. If they are produced 
naturally, the surface of the planet must be cracked in many places. It is generally 
thought that terrestrial volcanoes lie along subterranean cracks that do not reach the 
surface. The volcanoes of the great chain of the Andes lie along a straight crack 
reaching from southern Peru to Terra del Fuego, 2500 miles in length. The vol- 
canoes of the Aleutian Islands lie along a curved crack equally long. Since other 
shorter lines of volcanoes are very numerous upon the Earth, and since countless 
others existed in former times, the cracks in the Earth's crust must be exceed- 
ingly numerous. Every dike and mineral vein indeed bears witness to this fact. 
There is no reason why terrestrial cracks should not be as numerous as those upon 
the Moon. In the case of the Earth they have usually been closed, sometimes by 
liquid matter from below, and sometimes by surface denudation. There is one 
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