March, 1907.] 



KNOWLEDGE & SCIENTIFIC NEWS. 



03 



top by the last escaping lava, and sometimes it is left open. 

 These spiracles are found of all sizes, from one measuring 

 three or four inches in diameter, up to another measuring 

 100 feet. 



V:'A 



Fig. 6. — Theophilus. 



On the surface of the moon are two kinds of rills, 

 some of which are probably elongated craters or grooved 

 valleys, and rills proper. The rills proper are ex- 

 tremely numerous on the moon, and about a thousand 

 are known 

 and identi- 

 fied. The 

 Ariadseus rill 

 (shown in 

 Fig. 4) is the 

 widest and 

 most con- 

 spicuous of 

 t h e m. I t 

 measures 

 three miles 

 in breadth by 

 a little over 

 half a mile in 

 depth. Like 

 all true rills, 

 its course is 

 approxim- 

 ately straight 

 or made up 

 of curves of 

 long radius. 

 E vident 1 y . 

 like terres- 

 trial dikes or 

 mineral v< 1 is 

 it has been 

 partially 

 filled upfrom 



1> :l0W. ( (tiler 



narrower rills apparently of great depth are found on 

 the moon. The general view that they are simply 

 cracks in the lunar surface is accepted by Professor 

 Pickering as correct. They occur most frequently in 

 formations of the secondary period; that is, in the dark 

 surfaces; or, if found in the primary formations, it is 

 where the surface has apparently been softened, and 

 partially flattened out by the application of heat, as in 

 the present instance. Rills are frequently found on the 

 edge of the lunar lava seas. A large crack is found in 

 Kilauea in precisely this position. It is from six to 

 eight feet wide, and from 20 to 30 feet deep near the 

 bridge. It is about a mile in length. A crack 5 to 20 

 feet in breadth, and 40 to 200 feet in depth, and 16 miles 

 in length is located south-west of the crater, and a 

 similar one lies parallel to it. The cracks themselves 

 have been partially filled up, but one said to be 1,500 

 feet in depth, is situated not far from the sixth crater 

 near Kelanea. 



Professor Pickering devotes some attention to the 

 question of water and vegetation on the moon. "It 

 is," he says, " a favourite argument of those who denv 

 that water ever existed on the moon, to say that if such 

 were the case signs of erosion would be found on its 

 surface. In the case of the earth, where vast bodies 

 of water are present, these signs are very pronounced 

 in the eroded valleys of mountain regions and the 

 alluvial plains of the more open country. When we 

 search the coarser detail on the moon no such signs are 

 found. . . . But, if the moon ever possessed any 

 water at all, it must have been in comparatively small 

 quantities, and we should accordingly look among it^ 

 finer detail for any evidence of its former existence. 

 Fig. 6 represents Theophilus, a crater 64 miles in dia- 

 meter. The central peaks rise 5,000 to (1,000 feet above 

 the crater floor and are indented by numerous deep 

 vallevs, four being clearly shown in the photograph. 

 It is believed that these valleys are due to erosion, and 

 are analogous to those shown in Fig. 7, which repre- 

 sents a mountain ridge behind Honolulu. The pre- 



l : lg. 7.— Kroslon Vallcys'in Hawaii. 



