VI. 



The Surface of the Moon. 1 



IN the January number of Natural Science, attention was directed 

 to two short articles on the subject of lunar volcanoes and lunar 

 glaciation. In the Bulletin of the Philosophical Society of Washington 

 (vol. xii., April. 1893, PP- 241-292) will be found a paper on "The 

 Moon's Face, a Study of the Origin of its Features," being the 

 retiring address of the President, Professor G. K. Gilbert. This is 

 an admirable summary of the history of the study of the moon's 

 surface, while, at the same time, it abounds with suggestive and 

 thoughtful ideas. Professor Gilbert commences by remarking that 

 the topography of the moon is perhaps better mapped than that of 

 North America, and mentions the various features which have been 

 observed and named. The " craters " are described, and figures are 

 given, comparisons being drawn between the " wreath " of a lunar 

 "crater" and the landslip terraces of the margin of a basaltic plateau. 

 After this descriptive matter, the various " theories " are taken into 

 consideration. Regarding the " volcanic theory," Professor Gilbert 

 compares unfavourably the relative abundance of the craters on the 

 moon with any equal area on the surface of the earth, those on the 

 earth being as one-tenth to those on the moon. The same disparity 

 exists with respect to size, the ten largest terrestrial craters recorded 

 having a mean diameter of eleven miles. These are, Lake Bourbon 

 (Luzon), 16 by 14 miles ; Asosan, 15 miles ; Kamschatka (Scrope, 

 2nd ed., p. 457), 15 miles ; Mauritius (Darwin), 15 by 11 miles ; Lake 

 Bolerna (Italy), 11 by 9 miles; Lake Maninju (Sumatra), 15 by 7 

 miles; Pepandayan, 15 by 6 miles; Teneriffe, 7 by 8-10 miles; 

 Deception Island, 8 by 7 miles ; Monte Cavo, 7 miles ; Mount 

 Marindin (Mindanao), 9 miles ; Mount Astria (Iceland) 10 miles. 

 The mean diameter for the ten largest lunar craters visible to us is 

 275 miles. These are, Apennines, Serenitatis, Crisium, Humorum, 

 Humboldtianum, Bailly, Iridium, Clavius, Otto Struve, and Gri- 

 maldi. The actual largest terrestrial crater has a diameter of about 

 fifteen miles, the largest lunar crater, that whose rim is partially 

 preserved in the Carpathian-Apennine-Caucasus chain, has a 



1 Precis of Professor G. K. Gilbert's address to the Philosophical Society of 

 Washington, December 10, 1892. By C. Davies Sherborn, F.G.S. 



