Progress of Astronomy during the Year 1879. 461 
gives a catalogue of 222 stationary meteors in the M.N., Xt., 
406. 
A paper by Dr. Ball, entitled “Speculations on the source of 
Meteorites,” is published in the Proceedings of the Royal Irish 
Academy (2nd series, II. p. 227). The author starts from the 
result of M. Tschermak’s investigations, that meteorites have had 
a volcanic source on some celestial body. He shows first that 
they cannot have come from the moon, as a projectile thrown from 
the moon, and once missing the earth, can never fall thereon, so that 
we should have to suppose the lunar volcanoes to be still in activity 
if the meteorites falling on the earth at present should have come 
from the moon. In order to get over the large initial velocity, 
which would be necessary to overcome the gravitation of a large 
planet, it seems then natural to inquire if a volcano on one of the 
minor planets could accomplish the task. Supposing a voleano 
of sufficient power (and if the projectile should cross the earth’s 
track, the initial velocity could not be much less than that re- 
quired to throw a projectile away from the earth) was placed on 
Ceres, for instance, would it be likely that a projectile driven 
therefrom, would ever cross the earth’s track? If the total 
velocity with which it leaves the orbit of Ceres be less than eight 
miles per second, then the projectile will fall short of the earth’s 
track; on the other hand, if the total-initial velocity exceeds six- 
teen miles, the orbit will be hyperbolic, and though it may cross 
the earth’s track once, it will never do so again. Taking a mean 
between these extreme velocities, suppose, that a projectile is 
discharged from a point in the orbit of Ceres, with an initial 
velocity of twelve miles in a random direction, what is the proba- 
bility that its orbit shall cross the earth’s track? When this 
problem is solved in accordance with the calculus of probabilities, 
it is found that the chances against that occurrence are about 
50,000 to one. But while none of the other planets, large or 
small, are likely to be the source of the meteorites, one planet, 
the earth itself, has special claims to consideration, as every pro- 
jectile launched into space by primeval powerful volcanoes must 
continue to revolve round the sun in orbits which cross the 
earth’s track in the point from which the projectile was originally 
discharged. At the point of crossing, of course a meeting of such 
a body and the earth will often happen. Assuming, therefore, 
