THE MOON’S FACE. 
259 
attractive power of the moon, its velocity on reaching the 
surface will be one and one-half miles per second ; and the 
equivalent energy, if all converted into heat and all stored 
in the mass of the falling body, would suffice to raise its 
temperature, supposing it to consist of ordinary volcanic rock, 
through 3,500 degrees of the Fahrenheit scale. In other 
words, the quantity of heat developed would -be greater by 
one-half than that necessary to fuse the body. The average 
velocity of shooting stars is estimated at 45 miles per second, 
or thirty times that of a body falling freely to the moon, and 
it is easy to understand that the heat developed by the sudden 
arrest of a fragment of rock traveling with such speed might 
serve not only to melt the fragment itself, but also to liquefy 
a considerable tract of the rock mass by which its motion 
w T as arrested. 
It is convenient to mention in this place a special phase 
of the meteoric theory which, though not devised to avoid 
this difficulty, nevertheless does avoid it. Meydenbauer, 
as a corollary of certain conclusions in regard to meteoric 
matter, holds that the surface of the moon is clothed 
with a mantle of cosmic dust, a deep layer of loose par¬ 
ticles everywhere concealing the solid nucleus, and that 
the fall thereon of aggregates of similar dust produced the 
lunar craters. By experimention with various finely divided 
substances he has in this way produced small craters simu¬ 
lating several of the lunar varieties. His results show raised 
rims analogous to the lunar wreath, central hills, and arched 
inner plains, such as characterize a few of the lunar craters. 
His published results do not include level inner plains, nor 
the association of inner plains with central hills; but, on 
the other hand, he does not extend this process to the largest 
craters and the maria. For them he suggests the collision 
of solid stars of sulphur or phosphorus, originally moons of 
the earth’s system, and he recognizes fusion as one of the 
results of their collision.* 
The third difficulty is found in the relation of the volume 
*A. Meydenbauer: Sirius, February, 1882. 
