56 



KNOWLEDGE & SCIENTIFIC NEWS. 



[March, 1907. 



cipitation cannot have come from a general atmospheric 



1 in ul. Hum. hut more likely from steam expelled from the 



Fig. 8.— Terrestrial Valley or Canal near Kilauea. 



chain of the Andes lie along a straight " crack " reach- 

 in- from Southern Peru to Terra del Fuego, 2,500 



miles m length. I he 

 volcanoes of the 

 Aleutian Islands lie 

 along a curved crack 

 equally long. Since 

 other shorter lines of 

 volcanoes are very 

 numerous on the 

 earth, and since 

 countless others ex- 

 isted in former times, 

 the cracks on the 

 earth's crust must be 

 exceedingly numer- 

 ous. Every mineral 

 dike and vein, in- 

 deed, bears witness 

 to this fact. There 

 is no reason why 

 terrestrial cracks 

 should not be as 

 numerous as those 

 on the moon. In the 

 case of the earth 

 they have usually 

 been closed, some- 

 times by liquid 

 matter from below 

 and sometimes by 

 surface denudations. 

 There is one 



openings of the spiracles in the central peaks themselves. 

 The lunar day is 29.V terrestrial days in length, and, 

 from the standpoint of climate, might almost be called 

 a lunar year, for the temperature rises from some 250 

 degrees below freezing to a height as great as that 

 experienced on the earth's equator, in the course of 14 

 or [5 days of sunshine. It has been observed that 

 some spots on the moon grow darker in this period, and 

 Professor Pickering attributes the darkening to the 

 springing up of vegetation. In the crater of Eras- 

 tosthenes, which is about 40 miles in diameter, he has 

 perceived two dark spots on the crater floor, and has 

 noted that these spots change, disappear, or increase, as 

 the long lunar day progresses from sunrise to sunset. 

 There are two snow-white central peaks in the crater, 

 and the dark spots (of vegetation?) are joined by lines, 

 which, to Professor Pickering's mind, resemble the 

 canals of Mars. In studying Erastosthenes in 1904 

 Professor Pickering found its interior seamed with 

 numerous fine cracks. Watching some of these cracks 

 soon after the sun rose on them he was able to see 

 them broaden out and change gradually into canals. 

 It is his belief that the cracks gave out water vapour, 

 which fertilised the vegetation along their sides and in 

 their neighbourhood, and that it was the growth ol this 

 vegetation which produced the appearance of a canal. 

 A further inference is that the canals on Mars, which 

 become more clearly visible at some periods of the year, 

 owing - to the melting of the Martian Polar ii e cap and 

 the flooding of the waterways, are similar cracks on 

 the surface of Mars. Cracks of the kind occur on the 

 moon. The largest of them is that known as Sirsalis, 

 which is 400 miles in length. It is possible also that 

 they exist on the earth, though they are not readily 

 discernible. It has sometimes been supposed that 

 tern -trial volcanoes lie .deny subterranean (-racks that 

 do not reach the surface. The volcanoes "I the great 



Fig. p.— Sinus Iridum. A Crater Ring on the Moon. 



crack, however, which comes to the surface in various 

 places in Eastern Asia and Western Africa, and stretch- 

 ing from the Dead Sea to Lake Nyassa, reaches the 

 enormous length of 3,500 miles That is about the 

 same length as the longest of the Martian canals. 



