360 



KNOWLEDGE. 



[August 1, 1898. 



craters and pit-like depressions are due to the action of 

 hot springs which have not flowed continuously, but that 

 water has from time to time issued from vents in the soil, 

 and has melted the ice above the vent ; the water is then 

 supposed to have 

 flowed back to the 

 warm interior of the 

 moon, takmg with 

 it a part of the sur- 

 face ice that has 

 been melted, and by 

 a series of such ebbs 

 and flows Mr. Peal 

 conceives the ter- 

 raced walls of the 

 lunar craters to 

 have been built up 

 above the level of 

 surrounding plains. 

 Putting on one side 

 the difficulty of con- 

 ceiving of nearly 

 perpendicular ice 

 clififs of 17,000 to 

 20,000 feet high, 

 standing for ages 

 without flowing 

 down as glaciers to 

 the plains at their 

 feet, we have to 

 account for the fact 

 that the lunar plains 

 and the floors of the 

 deeper limar cra- 

 ters are generally 

 of a much darker 

 tint than the higher 

 ground upon the 

 moon ; while if the 

 whole of the lunar 

 surface were com- 

 posed of ice and 

 snow there would 

 be no reason for 

 such a difference of 

 tint, unless, as Mr. 

 Peal suggests, the 

 lunar plains are 

 surfaces of \'irgin 

 ice while the moun- 

 tains are formed of 

 snow. But virgin 

 ice would reflect 

 the light of the 

 sun specularly, and 

 in the equatorial 

 and tropical parts 

 of the moon from 

 which the sun's 

 rays could be 



From ii iihotiigrupli of thf Aloon takfii lij thr Ui'dI liiis liciii-\ on the 

 29th Mureh, 1«90. 



mapped (Rectus) as 16 by 14 miles in extent; (2) the crater of 

 Asosan, Isle of Kiushiu, Japan, is 15 miles across (Milne); (3) 

 Scrope mentions a circular crateriform lake, about i5 miles in 

 •liameter, in Northern Kamschatka ("Volcanoes," second edition, 

 London, 1H02, ]>. 4.57) ; (4) an imperfect crater cirque on Mauritius, 

 mentioned by Charles Darwin, is mapped (A.lniiraltj) as about 15 by 

 16 miles in extent ; (3) the crater walls surrounding Lake Bolesna, 

 Italy, are mapped as H by 9 miles in extent ; (6) the crater con- 

 tainmg Lake Maninju, Sumatra, is mapped (Reclus) as 15 bv 7 miles 

 in extent. 



specularly reflected to us there are no traces of such 

 specular reflection. The theory also fails to account 

 for the small craters frequently found on the rims of 

 larger craters and on the sloping sides of mountains; 



such small craters 

 are far above the 

 assumed rock sur- 

 face of the moon and 

 warm water issuing 

 from them would 

 flow down the sides 

 of the mountains, 

 leaving marked 

 traces of its flow. 



The meteoric 

 theory of the forma- 

 tion of lunar craters 

 has also had many 

 advocates. It is 

 alleged that if a 

 pebble be dropped 

 into mud the scar 

 produced has a 

 raised rim and a 

 central hill, which 

 resembles a lunar 

 crater. Even Mr. 

 Proctor had an in- 

 clination for this 

 theory. At page 346 

 of his book on the 

 moon, he says : — 

 " So far as the 

 smaller craters are 

 concerned, there is 

 nothing incredible 

 in the supposition 

 that they were due 

 to meteoric rain 

 falling when the 

 moon was in a plas- 

 tic condition. In- 

 deed, itis somewhat 

 remarkable how 

 strikingly certain 

 parts of the moon 

 resemble a surface 

 which has been 

 rained upon, while 

 sufficiently plastic 

 to receive the im- 

 pressions, but not 

 too soft to retain 

 them. Nor is it any 

 valid objection to 

 this supposition, 

 that the rings left by 

 meteoric downfall 

 would only be circu - 

 lar when the falling 

 matter chanced to strike the moon's surface squarely ; for 

 it is far more probable that even when the surface was 

 struck obUquely, and the opening first formed by the 

 meteoric mass or cloud of bodies was therefore markedly 

 elliptic, the plastic surface would close in round the place 

 of impact until the impression actually formed had 

 assumed a nearly circular shape." After inviting attention 

 to the lunar photographs published with his book, Mr. 

 Proctor continues: — "It will be seen that the multi- 



