Tschermak's view of the volcanic origin of
the meteorites lies in the tremendous initial velocity which is
required. The Columbiad is a myth, and we know no agent, natural or
artificial, at the present time on the earth, adequate to the production
of a velocity so appalling. The thunders of Krakatoa were heard
thousands of miles away, but in its mightiest throes it discharged no
missiles with a velocity of six miles a second. We are therefore led to
enquire whether any of the other celestial bodies are entitled to the
parentage of the meteorites. We cannot see volcanoes on any other body
except the moon; all the other bodies are too remote for an inspection
so minute. Does it seem likely that volcanoes on the moon can ever
launch forth missiles which fall upon the earth?

This belief was once sustained by eminent authority. The mass of the
moon is about one-eightieth of the mass of the earth. It would not be
true to assert that the critical velocity of projection varies directly
as the mass of the planet. The correct law is, that it varies directly
as the square root of the mass, and inversely as the square root of the
radius. It is hence shown that the velocity required to project a
missile away from the moon is only about one-sixth of that which would
be required to project a missile away from the earth. If the moon had on
its surface volcanoes of one-mile power, it is quite conceivable that
these might be the source of meteorites. We have seen how the whole
surface of the moon shows traces of intense volcanic activity. A missile
thus projected from the moon could undoubtedly fall on the earth, and it
is not impossible that some of the meteorites may really have come from
this source. There is, however, one great difficulty about the volcanoes
on the moon. Suppose an object were so projected, it would, under the
attraction of the earth, in accordance with Kepler's laws, move around
the earth as a focus. If we set aside the disturbances produced by all
other bodies, as well as the disturbance produced by the moon itself, we
see that the meteorite if it once misses the earth can never fall
thereon. It would be necessary that the shortest distance of the earth's
centre from the orbit of the projectile should be less than the radius
of the earth, so that if a lunar meteorite is to fall on the earth, it
must do so the first time it goes round. The journey of a meteorite from
the moon to the earth is only a matter of days, a