METEORS.
Meteors are the tramps of interplanetary space. They sometimes try to
steal a ride on the surface of the earth, but meet with certain
destruction the moment they come within the aerial picket line of our
world's defense against these wandering vagrants of the air. They have
made many attempts to take this earth by storm, as it were, and many
more will be made. They fire their missiles at us by the millions every
year with a speed that is incredible, but thanks to the protecting
influence of the great ocean of air that envelops our globe they become
the victims of their own velocity.
Meteors or shooting stars are as old as the earth itself, and they are
the material of which comets are made. Before it was determined what
these meteors or shooting stars were, many theories were promulgated as
to their origin. One was that they were masses of matter, large and
small, projected by volcanic action from the face of the moon with such
violence as to be brought within the attraction of the earth. Others
supposed them to be the effect of certain phosphoric fluids that
emanated from the earth and took fire in the upper regions of the
atmosphere. This, however, was mere speculation and without any
scientific basis of fact. Anyone who has been an observer of shooting
stars will have learned that there are certain periods of the year when
they are more numerous than at other times; notably in August and
November. Then again there are longer periods of many years apart. By
persistent observation it has been established that there are great
numbers of schools or collections of cosmic matter that fly through
interplanetary space, having definite orbits like the planets. Any one
of these collections may be scattered through millions of miles in
length. A comet is simply one of these wandering collections of meteoric
stones having a nucleus or center where the particles are so condensed
as to give it a reflecting surface something like the planets or the
moon. This enables us to see the outline of the comet to the point where
the fragments of matter become so scattered that they are no longer able
to reflect sufficient light to reach our eyes. The fringe of a comet,
however, may extend thousands or even millions of miles beyond the
borders of luminosity.
There is scarcely a day or night in the year when more or less of these
meteoric stones do not come within the region of our atmosphere, and
when this happens the great velocity at which they travel is the means
of their own destruction. They become intensely heated by friction
against the atmosphere just as a bullet will when fired from a gun--only
to a greater extent owing to the greater velocity. They disintegrate
into dust which floats in the air for a time, when more or less of it is
precipitated upon the surface of the earth. Disintegrated meteors, or
star dust, as they are sometimes called, are often brought down by the
rain or snow. Most of the shooting stars that we observe are very small,
resembling fire-flies in the sky, but once in a while a very large one
is seen moving across the face of the heavens, giving off brilliant
scintillations that trail behind the meteor, making a luminous path that
is visible for some seconds. These brilliant manifestations are due to
one of two causes. Either there is a very large mass of incandescent
matter or else they are so much nearer to us than in ordinary cases that
they appear larger. It is more likely, however, that it is due to the
former cause rather than the latter, from the fact of its apparently
slow movement as compared with the smaller shooting stars. It has been
determined by observation that the average meteor becomes visible at a
point less than 100 miles above the earth's surface. It was found as far
back as 1823 that out of 100 shooting stars twenty-two of them had an
elevation of over twenty-four and less than forty miles; thirty-five,
between forty and fifty miles; and thirteen between seventy and eighty
miles. It was determined by Professor Herschel that out of sixty
observations of shooting stars the average height of their first
appearance was seventy-eight miles and their disappearance was at a
point fifty-three miles above the earth.
It is a matter of history, however, that sometimes these meteoric stones
descend to the surface of the earth before they are entirely
disintegrated. A fine specimen of this kind is to be seen in the
Smithsonian Institution. There are over forty specimens of these
aerolites (air-stones) in the British Museum, labeled with the times and
places of their fall. Instances of falling to the earth are so rare that
there is little to fear from these wandering missiles of the air. We do
not remember a case where life or property has suffered from the fall of
a meteor.
This brings us to the consideration of the part which the great air
envelope surrounding the earth plays as a protection against many
outside influences. For instance, if it were not for the air, millions
of these meteoric stones would be showered upon our earth every year and
at certain times every day, which would render the earth untenable for
human existence. We should be at the mercy of those wandering comets
whose fringes strike our atmosphere more or less deeply at frequent
intervals. It is not impossible that the earth may at some time pass
directly through one, and yet there is little danger that in such a case
there would be more than an unusual display of celestial fireworks.
From the facts that have been above stated it will be apparent to anyone
that the number of these meteoric stones in the air is being constantly
reduced by their constant collision with the atmosphere and consequent
reduction to ashes or dust. Another conclusion is that the earth must be
gradually, but imperceptibly perhaps, increasing in size on account of
the constant settling upon its surface of meteoric dust.