The
question is, Whence comes this light? It must be light without heat,
since the fine dust or vapor of which the train can only consist would
not retain sufficient heat to render it luminous for so long a time.
An extremely remarkable incident of this kind occurred on February 22,
1909, when an immense fire-ball that passed over southern England left
a train that remained visible during two hours, assuming many curious
shapes as it was drifted about by currents in the air.
But notwithstanding the enormous velocity with which meteorites enter
the air they are soon slowed down to comparatively moderate speed, so
that when they disappear they are usually traveling not faster than a
mile a second. The courses of many have been traced by observers
situated along their track at various points, and thus a knowledge has
been obtained of their height above the ground during their flight and
of the length of their visible courses. They generally appear at an
elevation of eighty or a hundred miles, and are seldom visible after
having descended to within five miles of the ground, unless the
observer happens to be near the striking-point, when he may actually
witness the fall. Frequently they burst while high in the air and
their fragments are scattered like shrapnel over the surface of the
ground, sometimes covering an area of several square miles, but of
course not thickly; different fragments of the same meteorite may
reach the ground at points several miles apart.
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