s proportional to the square
of the velocity. The meteor in passing through the air may therefore
develop by the friction of the air about ten thousand times as much heat
as the rifle bullet. We do not make an exaggerated estimate in supposing
that the latter missile becomes heated ten degrees by friction; yet if
this be admitted, we must grant that there is such an enormous
development of heat attending the flight of the meteor that even a
fraction of it would be sufficient to drive the object into vapour.

Let us first consider the circumstances in which these external bodies
are manifested to us, and, for the sake of illustration, we may take a
remarkable fireball which occurred on November 6th, 1869. This body was
seen from many different places in England; and by combining and
comparing these observations, we obtain accurate information as to the
height of the object and the velocity with which it travelled.

It appears that this meteor commenced to be visible at a point ninety
miles above Frome, in Somersetshire, and that it vanished twenty-seven
miles over the sea, near St. Ives, in Cornwall. The path of the body,
and the principal localities from which it was observed, are shown in
the map (Fig. 75). The whole length of its visible course was about 170
miles, which was performed in a period of five seconds, thus giving an
average velocity of thirty-four miles per second. A remarkable feature
in the appearance which this fireball presented was the long persistent
streak of luminous cloud, about fifty miles long and four miles wide,
which remained in sight for fully fifty minutes. We have in this example
an illustration of the chief features of the phenomena of a shooting
star presented on a very grand scale. It is, however, to be observed
that the persistent luminous streak is not a universal, nor, indeed, a
very common characteristic of a shooting star.

[Illustration: Fig. 75.--The Path of the Fireball of November 6th,
1869.]

The small objects which occasionally flash across the field of the
telescope show us that there are innumerable telescopic shooting stars,
too small and too faint to be visible to the unaided eye. These objects
are all dissipated in the way we have described; it is, in fact, only at
the moment, and during the process of their dissolution, that we become
aware of their existence. Small as these missiles probably are, their
velocity is so prodigious that they would render the earth uninh