1904 - 5 .] Mr Romanes on the Formation of the Moon. 
473 
aided by the disintegrating influence of the atmosphere and of the 
earth’s tidal attraction. The earth’s atmosphere would thus be the 
first and principal recipient of the heat caused in this way. 
Direct impacts on the earth would be rare, and their marks would 
in time be effaced by the various geological influences. 
Impacts on the moon, of bodies having independent orbits round 
the earth, would be of a very different nature ; these would often 
be very direct, and the bodies themselves might be of considerable 
size, possibly up to 20 miles or more in diameter. Such bodies 
being built up of many parts loosely held together by their own 
feeble gravity, would be more like masses of sand and dust than 
solid stone ; hence a grazing impact of such a body on the moon 
would be like a sand-blast which would liquefy the rock and plough 
out a straight groove. The utmost velocity the moon can produce 
by its attraction is 1476 mile per second, and bodies having orbits 
round the earth at the same mean distance in the opposite 
direction would, if they collided, strike it with the velocity of 1 - 946 
mile per second, and it would be struck by bodies having orbits 
within its own, as well as by others beyond it ; thus velocities of 
impact might range from 1 4 mile to even 2 miles per second on 
rare occasions. These velocities represent energies capable of 
raising the temperature of the bodies striking by 5200° Fahr. to 
10600° Fahr., or rather of raising the temperature not only of the 
bodies themselves, but also of much of the moon’s surface, to an 
extent sufficient to liquefy them ; while the mechanical force of 
the impact would cause much of the surrounding surface to be 
forced up into irregular mountain ranges all round, and cause 
great splashings of liquid rock from the hollows thus formed, and 
great surgings to and fro of the liquid rock within them ; and no 
doubt gases would be formed and fly off, till the liquid rock had 
time to cool. 
Besides being struck by single bodies, the moon may often have 
been struck and grazed by nebulae — that is to say, swarms of small 
bodies which had sufficient moments of momentum about their 
centres of mass to keep them from aggregating more closely. 
Impacts of large bodies having independent orbits round the sun 
would be very rare, and it is doubtful if any would leave marks 
large enough to be seen from the earth. 
