ets a planet. It cannot strike the actual
body of the planet--the atmosphere is a sufficient screen; the
tremendous friction reduces it to dust in an instant, and this dust then
quietly and leisurely settles down on to the surface.

Evidence of the settlement of meteoric dust is not easy to obtain in
such a place as England, where the dust which accumulates is seldom of a
celestial character; but on the snow-fields of Greenland or the
Himalayas dust can be found; and by a Committee of the British
Association distinct evidence of molten globules of iron and other
materials appropriate to aerolites has been obtained, by the simple
process of collecting, melting, and filtering long exposed snow.
Volcanic ash may be mingled with it, but under the microscope the
volcanic and the meteoric constituents have each a distinctive
character.

The quantity of meteoric material which reaches the earth as dust must
be immensely in excess of the minute quantity which arrives in the form
of lumps. Hundreds or thousands of tons per annum must be received; and
the accretion must, one would think, in the course of ages be able to
exert some influence on the period of the earth's rotation--the length
of the day. It is too small, however, to have been yet certainly
detected. Possibly, it is altogether negligible.

It has been suggested that those stones which actually fall are not the
true cosmic wanderers, but are merely fragments of our own earth, cast
up by powerful volcanoes long ago when the igneous power of the earth
was more vigorous than now--cast up with a speed of close upon seven
miles a second; and now in these quiet times gradually being swept up by
the earth, and so returning whence they came.

I confess I am unable to draw a clear distinction between one set and
the other. Some falling stars may have had an origin of this sort, but
certainly others have not; and it would seem very unlikely that one set
only should fall bodily upon the earth, while the others should always
be rubbed to powder. Still, it is a possibility to be borne in mind.

We have spoken of these cosmic visitors as wandering masses of stone or
iron; but we should be wrong if we associated with the term "wandering"
any ideas of lawlessness and irregularity of path. These small lumps of
matter are as obedient to the law of gravity as any large ones can be.
They must all, therefore, have definite orbits, and these orbits will
have reference to the main attr