Thus light travels two hundred and thn-
teen thousand miles in a second; and, as
the moon is two hundred and forty thousand
miles distant, it follows that, when the first
narrow streak of the moon emerges from the
shadow of an eclipse, nearly a second and
a quarter elapses before we see it ; for the



iiMP^h, Google



AND THE EARTH. 11

light takes this time to pass from the moon
to our eyes. The moon, therefore, makes
each of her changes a second and a quarter
before it becomes visible to us.'

The sun, ninety-five millions of miles dis-
tant, four hundred times farther than the
moon, requires a period four hundred times
longer than the moon (i. e. four hundred
times five quarters of a second) to send its
light upon our earth. Hence, when any
change takes place in the sun, when, for
instance, a solar spot creeps round the east-
ern limb, about eight minutes elapse before
the light reaches our eyes; and the spot
remains visible to us eight minutes after it
has passed behind the western limb.
The distance of the planet Jupiter from
our earth, at the time when it is the greatest,
is nearly six hundred and seventeen millions
of miles. This is six times and a half as
great as the distance of the sun, and there-
• We take no notice of the refraction of the light.
