When we throw a lump of coal on the fire, all that is soon left is a
little pinch of ashes, and the rest of the coal has vanished. You might
think it had been altogether annihilated, but that is not nature’s
way. Nothing is ever completely destroyed; it is merely transformed or
changed into something else. The greater part of the coal has united
with the oxygen which it has obtained from the air, and has formed a
new gas, which has ascended the chimney. Every particle that was in the
coal can be thus accounted for, and in the act of transformation heat
is given out.
A meteor also becomes transformed, but the substance it contains is not
lost, though it is changed into glowing vapors. It is known that with
heat enough any substance can be turned into vapor, just as water can
be boiled into steam. Look at an electric light flashing between two
pieces of carbon. Though carbon is one of the most difficult substances
to melt, yet such is the intense heat generated by the electric
current that the carbon is not only melted, but is actually turned
into a vapor, and it is this vapor glowing with heat that gives us the
brilliant light. In a similar manner iron can be rendered red-hot,
white-hot, and then boiled and transformed into an iron vapor, if we
may so call it. There is, indeed, plenty of such iron vapor in the
universe. Quantities of it surround the sun and some of the stars.
When ordinary steam is chilled it condenses into little drops of water.
So, too, if iron be heated until it is transformed into vapor, and if
that vapor be allowed to condense, it will ultimately form a dust,
consisting of bits of iron so small that you would require a microscope
to examine them. There is iron present in the small shooting stars.
Other substances are also contained therein, and all these materials,
after being boiled by the intense heat, are transformed into vapor.
When the heat subsides, the vapor condenses again into fine dust,
so that the ultimate effect of the atmosphere on a shooting star is
to grind the little object into excessively fine powder, which is
scattered along the track which the object has pursued. Sometimes this
powder will continue to glow for minutes after the meteor has vanished,
and in the case of some great meteors this stream of luminous dust in
the air forms a very striking spectacle. A great meteor, or fire-ball
as it is often called, appeared on the 6th of November, 1869. It flew
over Devonshire and Cornwall, and left a track fifty miles long and
four miles wide. The dust remained visible all along the great highway
for nearly an hour; it formed a glowing cloud hanging in the sky, and
though originally nearly straight, it became bent and twisted by the
winds before it finally disappeared from view.
We have now to see what becomes of this meteoric dust which is being
incessantly poured into the air from external space. None of it ever
gets away again; for whenever an unfortunate meteor just touches the
air it is inevitably captured and pulverized. That dust subsides
slowly, but we do not find it easy to distinguish the particles which
have come from the shooting stars, because there is so much floating
dust which has come from other sources.
A sunbeam is the prettiest way of revealing the existence of the motes
with which the air is charged. The sunbeam renders these motes visible
exactly in the same way as planets become visible when sunbeams fall
on them in far-distant space. But if we have not the sunbeams here,
we can throw across the room a beam of electric light, and it is seen
glowing all along its track, simply because the air of the room, like
air everywhere, is charged with myriads of small floating particles.
If you hold the flame of a spirit-lamp beneath this beam, you will see
what seems like columns of black smoke ascending through it. But these
columns are not smoke, they are pure air, or rather air in which the
solid particles have been transformed into vapor by the heat from the
spirit-flame.
The motes abound everywhere in the air. We take thousands of them
into our lungs every time we breathe. They are on the whole gradually
sinking and subsiding downwards, but they yield to every slightest
current, so that when looking at a sunbeam you will find them moving in
all directions. It is sometimes hard to believe that the little objects
are tending downwards, but if you look on the top of a book that has
lain for a time on a book-shelf, you find there a quantity of dust,
produced by the motes which have gradually subsided where they found a
quiet spot and were allowed sufficient time to do so.
The great majority of these particles consist, no doubt, of fragments
of terrestrial objects. The dust from the roads, the smoke from the
factories, and numerous other sources, are incessantly adding their
objectionable particles to the air. There can be no doubt that the
shooting stars also contribute their mites to the dust with which the
atmosphere is ever charged. The motes in the murky air of our towns
have no doubt chiefly originated from sources on this earth. Many
of these sources it would be impossible to regard as of a romantic
description. We may, however, feel confident that among those teeming
myriads of small floating objects are many little particles which,
having had their origin from shooting stars, are now gradually sinking
to the earth.
This is not a mere surmise, for dust has been collected from lofty
Alpine snows, from the depths of the sea, and from other localities far
removed from the haunts of men. From such collections, tiny particles
of iron have been obtained, which have evidently been once in a molten
condition. There is no conceivable explanation for the origin of iron
fragments in such situations, except that they have been dropped from
shooting stars.
I am sure you have often helped in the making of a gigantic snowball.
You begin with a small quantity of snow that can be worked with your
hands. Then you have rolled it along the ground until it has become
so big and so heavy that you must get a few playmates to help you,
until at last it has grown so unwieldy that you can move it no longer,
and then you apply your artistic powers to carving out a statue. The
snowball has grown by the addition of material to it from without,
and as it became heavier and heavier, it lapped up more and more of
the snow as it rolled along; so that with each increase of size, its
capacity for becoming still larger has also increased. I want to liken
our earth to a snowball which goes rolling on through space, and
every day, every hour, every minute, is gathering up and taking into
it the little shooting stars that it meets with on its way. No doubt
the annual accumulation is a very small quantity when compared with the
whole size of the earth; but the earth is always drawing in, and now,
at all events, never giving back again; so that when this process is
carried on long enough, astonishing results may be obtained.
You have all heard many maxims on this subject--how every little saving
will at length reach a respectable or a gigantic total. Nature abounds
with illustrations of the principle. All the water that thunders over
Niagara is merely a sufficient number of little drops of rain collected
together. Our earth has been gradually hoarding up, during countless
ages, all the meteor dust that has rained upon it; and the larger the
earth grows, the bigger is the net which it spreads, and the greater is
the power it has to capture the wandering bodies. Thus, our earth, ages
and ages ago, may have been considerably smaller than it is at present;
in fact, a large proportion of this globe on which we dwell may have
been derived from the little shooting stars which incessantly rain in
upon its surface.