Mr J. D. Danta on the Volcanoes of the Moon, 21 



With so perfect a correspondence, and so satisfactory ex- 

 planations by means of an appeal to facts, it is hardly neces- 

 sary to enter a protest against the ordinary view, that these 

 craters are the result of cinder eruptions.* We remark only, 

 that such eruptions will never take place except from small 

 vents, for the cold which gives the viscidity on which they 

 depend, necessarily contracts the area. In a large pool the 

 fluidity is such, that the rising vapours pass off freely : the 

 ejections over its surface, excepting those at the margin, will 

 fall back again into the pool, as in boiling water and Kilauea, 

 and could neither rise to the height, nor make such curves, 

 as are represented by Mr Nasmyth. Instead of a large open 

 crater having greater projectile force in proportion to its 

 size, it will actually have far less ; and within certain limits 

 the force may be inversely as the diameter, though depend- 

 ent also on the size of the chimney above. 



Any vents in the moon in which the fires had partially sub- 

 sided, would have densely viscid lavas from partial cooling ; 

 and in these there would be loftier ejections like those of 

 ordinary volcanoes, forming high conical peaks with narrow 

 openings, if any, at summit. 



The great depth of the lunar pits seems to require another 

 element for its explanation, in addition to what has been pre- 

 sented. This is supplied by the fact of the less specific gra- 

 vity of substances on the moon ; for objects on its surface 

 have but one-sixth the specific gravity they have on the 

 earth : that is, iron would weigh but one-sixth what it does 

 here. The lavas would, therefore, not only be specifically 

 lighter, but would become more blown up with the vapours, 

 or more spongy. On the same ground, too, we understand 

 why the moon's great craters should so generally terminate 

 in a raised rim, while those of the earth, like Mount Loa, 

 have very gently sloping sides and summit. This raised rim 

 is fully illustrated about the Kilauea pools, as we have 

 already stated : but in large overflowings, the earth's lavas, 

 owing to their weight, flow far away by gravity, and this 



* Sec the views and remarks of Mr J. Nasmyth, loc, sit. 



