agnificence of
the object they were contemplating. No one, unaided by the teaching of
science, could have conceived that the streak of light, so readily
compressed within the narrow limits of an eye-glance, stretched out
170 millions of miles in length.

The comet comes from regions of unknown remoteness, and rushes, with
continually increasing speed, towards our own source of warmth and
light--the genial sun. When it has reached within a certain distance
of this object, it appears, however, to overshoot the mark of its
desire, as if too ardent in the chase, and then sways round with
fearful impetus, beginning reluctantly to settle out into space again,
and moving with less and less velocity as it goes, until its misty
form is once more withdrawn by distance from human sight. When the
comet of 1813 swept round the sun in this way, it was so near to the
shining surface of the solar orb, that it must have been rushing for
the time through a temperature forty-seven thousand times higher than
any which the torrid region of the earth ever feels. Such heat would
have been twenty-four times more than enough to melt rock-crystal. The
overburdened sense experiences a feeling of relief in the mere
knowledge, that the comet passed this fiery ordeal as the lightning's
flash might have done. In two short hours, it had shifted its place
from one side to the other of the solar sphere. In sixty little
minutes, it had moved from a region in which the heat was forty
thousand times greater than the fiercest burning of the earth's torrid
zone, into another, in which the temperature was four times less. The
comet might well have a glowing tail as it came from such a realm of
fire. Flames that were colder by many hundred times, would make the
dull black iron shine with incandescent brightness.

As, however, it is the comet's nature to guard its ornamental
appendages with jealous care, it may be conceived that this tail of
170 million miles might prove a somewhat troublesome travelling
companion in so rapid a journey. Comets always turn their tails
prudentially out of harm's way as they whisk through the neighbourhood
of the solar blaze. In whatever direction these bodies may be moving,
they are always seen to project their caudal beams directly _from_ the
sun. Imagine the case of a rigid straight stick, held by one end in
the hand, and brandished round through a half-circle. The outer end of
the stick would move through a considerable swee