nded with filmy
wrappings, appeared in the sky. The sun's light, diffused throughout
our atmosphere, had prevented its being seen sooner. This was apparently
the comet's head. It is described as 'though a number of light, hazy
clouds were floating around a miniature full moon.' From this a cone of
light extended far up into the sky, and when the head disappeared below
the horizon this tail was seen to reach to the zenith. But that was not
all. Strange shafts of light seemed to hang right overhead, and could
only be accounted for by supposing that they were caused by another tail
hanging straight above us, so that we looked up at it foreshortened by
perspective. The comet's head lay between the earth and the sun, and its
tail, which extended over many millions of miles, stretched out behind
in such a way that the earth must have gone right through it. The fact
that the comet exercised no perceptible influence on the earth at all,
and that there were not even any unaccountable magnetic storms or
displays of electricity, may reassure us so that if ever we do again
come in contact with one of these extremely fine, thin bodies, we need
not be afraid.

There is another way in which we can judge of the wonderful tenuity or
thinness of comets--that is, that the smallest stars can be seen
through their tails, even though those tails must be many thousands of
miles in thickness. Now, if the tails were anything approaching the
density of our own atmosphere, the stars when seen through them would
appear to be moved out of their places. This sounds odd, and requires a
word of explanation. The fact is that anything seen through any
transparent medium like water or air is what is called refracted--that
is to say, the rays coming from it look bent. Everyone is quite familiar
with this in everyday life, though perhaps they may not have noticed it.
You cannot thrust a stick into the water without seeing that it looks
crooked. Air being less dense than water has not quite so strong a
refracting power, but still it has some. We cannot prove it in just the
same way, because we are all inside the atmosphere ourselves, and there
is no possibility of thrusting a stick into it from the outside! The
only way we know it is by looking at something which is 'outside'
already, and we find plenty of objects in the sky. As a matter of fact,
the stars are all a little pulled out of their places by being seen
through the air, and though of course we do