1904 - 5 .] Mr Eomanes on the Formation of the Moon. 477 
The velocity of impact in these experiments is not known, but 
might have been about 1200 feet per second; and, no doubt, 
bullets fired at higher velocities would form cavities wider in 
proportion to the bullet. A velocity of 1200 feet per second is 
from one-sixth to one-ninth of the velocities we are dealing with 
in the case of the moon, and the body striking is a compact one ; 
whereas, as has been shown above, the bodies striking the moon 
were by no means compact ; and the circumstances are so different 
that the analogy between the bullet marks and the lunar craters 
will not be very close. However, the experiments make it clear 
that cavities so formed on the moon’s surface may be expected to 
be greatly larger in diameter than the body that caused them, and 
generally fairly round. 
The great radial streaks, notably those from Tycho, are probably 
caused by splashes of liquid rock comminuted and blown out by 
the gas formed at the same time. Their great brilliancy at full 
moon is probably due to the surface being rough — that is, covered 
with small particles, and not appearing vitrified like the rest of 
the moon’s surface. As no shadows can be seen at full moon, 
rough surfaces must then appear brighter than under indirect 
illumination. Although these streaks extend to great distances, 
such as 1000 miles, it is obvious that the initial velocity, neces- 
sary to project them from their source to any other part of the 
moon’s surface, is much less than the moon caused by its attraction 
on the bodies that produced them ; and therefore this cause of 
them is quite within the limits of possibility. 
The irregular terraces or wrinkles, seen on both the inner and 
the outer slopes of the circular mountain rings, and particularly 
well seen in Copernicus, are probably caused by the powerful side 
thrust that raised them up. 
The cones inside the craters are evidence that part of the body 
striking was unmelted, and was piled up in a heap or heaps near 
the centre, and cemented together by the liquid rock surging to 
and fro. The absence of cones in some craters shows that the 
whole has been melted, either at first or by lava from other sources, 
such as molten lava being thrown in by the violent surgings of 
the maria when they were formed. 
The Valley of the Alps has all the appearance of having been 
