172 



KNOWLEDGE. 



[September 1, 1898. 



Fig. 8. — Aroliimedes and the smaller 

 Crater Timoeharis. 



tions of this great volcano. If this theory affords the true 



explanation of these dark markings, it would follow that 



in this region of the moon the colour of the lunar surface 



is not masked by snow or other white deposit which is 



being continually deposited and evaporated. 



If the reader will examine Plate II., he will see just to 



the north of Timoeharis a curious narrow dark circle with 



a dark centre. After having made sure of this marking 



on Plate 11., he will be 

 able just to recognize 

 the southern half of the 

 circle on a good print 

 of Plate I. It would 

 almost seem as if we 

 had here a section of a 

 volcano dissected by 

 denudation, or the relic 

 of a crater and its vol- 

 canic throat which had 

 been cut off or melted 

 down when the Mare 

 Imbrium was surfaced. 



We have evidently much to learn from these mysterious 



dark marliings. 



Terrestrial volcanoes will sometimes pour out a dark- 

 coloured lava at one eruption and a grey or whiLish lava 



at the next. The colour of the lava seems to depend on 



the character of the rocks melted at no great distance 



beneath the 



surface, for 



if the lavas 



all came from 



one general 



reservoir at 



the centre of 



the earth we 



should expect 



them all to 



be similar in 



chara c t e r. 



And if upon 



the moon 



we were to 



find lavas of 



d i ff e rent 



colours, we 



might take it 



as evidence 



that the moon 



Fig. 9. — Copernicus, 

 from 



showing dark streams 

 crater. 



is either stratified or formed of different 

 materials in different parts. 



There are no very striking 

 differences of colour or even 

 of tint to be detected on 

 the moon, but there are very 

 striking difl'erences of white- 

 ness of the lunar surface, and 

 it becomes a very interest- 



ing question 

 whether these 

 whiteness are 

 difl'erences in 

 lunar rocks, or 



to determine 



differences of 



really due to 



colour of the 



whether they 



are due of something which 

 covers the lunar surface in 

 some places and leaves the 

 dark rocks exposed in others. 

 Thus, as has been suggested, 

 the dark regions might be 

 caused by the action of warm springs, which on the earth. 



Fig. 10.— Dark patches on 

 the western slope of 

 Copernicus. 



always accompany volcanic action. But even if we are 

 ready to conceive of warm springs so copious as to affect 

 areas as large as those corresponding to the streams which 

 seem to have flowed from Copernicus, it seems improbable 

 that warm springs could affect the colour of large areas such 

 as the dark patches on the western slope of Copernicus 

 or the great Maria. As a general rule, plains and low- 

 lying ground upon the moon are dark, while the high 

 groimd and mountain-tops are white, and some lunar 

 moimtains are much whiter than others. This very 

 markedly points to the conclusion that the whiteness is 

 due to something covering the lunar rocks, and that the 

 covering is more thickly deposited on high ground, as 

 snow is on terrestrial mountains. 



The dark markings to which attention is here directed 

 are those which retain their relatively dark appearance as 

 the sun rises, and which can still be traced at full moon ; 

 they cannot, therefore, be explained as due to rough sur- 

 faces, causing an admixture of shadow that darkens the 

 natural tint. The narrow dark line between the craters 

 Birt and Thebit, in the top left- 

 hand corner of Plate I., is clearly 

 due to a shadow, for it becomes 

 narrower as the sun rises, and is 

 ultimately lost sight of. 



The curious dark spots on the 

 floors of many hmar craters, and 

 markings like that to the north of 

 Timoeharis, however, point to the 

 conclusion that there are striking 

 differences in the light-reflecting 

 power of areas which appear to 

 correspond with lunar volcanic 

 formations, and they further point 

 to the conclusion that there is 

 a real difference in the colour 

 of the lunar rocks, or that there 



are local differences of temperature, or other local causes 

 corresponding to such formations, which affect the covering 

 that masks the true colour of the hmar surface. But it 

 must be remembered that difl'erences of colour of the lunar 

 rocks, if conclusively proved to exist, would not prove 

 that the rocks were difl'ereut in composition, for differences 

 of tint may be due to weathering action ; thus, many 

 terrestrial lavas when first formed are black, but they 

 subsequently become reddish or brown. 



Fig. 11. — The Riphican 

 Mountains. 



Science Notes. 



The mass of the earth, as re-determined by M. Alphonse 

 Berget, is 5-85 x 10-' grammes, its density 5-41. 



The Lancet refers to the confirmed " stoop" which has 

 already been manifested by cyclists. The dorsal curvature 

 posteriorly, which used to be rare in boys under fourteen 

 years of age, is now very frequently met with, particularly 

 among those bicyclists whose spinal column is developing 

 more rapidly than the ligaments and muscles. The use 

 of Indian clubs is recommended. 



A novel kind of cab has lately been tried in Berlin. In 

 appearance it is not unlike a large bath chair with two 

 scats, and is propelled by a petroleum-naphtha motor. It 

 has three wheels, and carries only two persons, including 

 the driver. The motor is of nearly two horse power, and 

 produces, on good roads, a speed of about eleven miles an 

 hour. 



