The curved lines represent the
gradual progress of the shadow during the eclipse named. This diagram,
ignoring the curved lines actually marked on it, may be used over and
over again for any number of eclipses, simply noting from the _Nautical
Almanac_ or other suitable ephemerides the points on the Moon's disc at
which the shadow first touches the disc as it comes on, and last touches
the disc as it goes off. The _Almanac_ indicates these points by
stating that the eclipse begins, or ends, as the case may be, at a point
which is so many degrees from the N. point of the Moon measured round
the Moon's circumference by the E. or by the W. as the case may be.

One other point and we have disposed of eclipses of the Moon. The shadow
which we see creeping over the Moon during an eclipse is, as we know,
the shadow cast by the Earth. If we notice it attentively we shall see
that its outline is curved, and that it is in fact a complete segment of
a circle. Moreover that the circularity of this shadow is maintained
from first to last so far as we are able to follow it. What is this,
then, but a proof of the rotundity of the earth? This shape of the
Earth's shadow on the Moon during a lunar eclipse was suggested as a
proof of the rotundity of the Earth by two old Greek astronomers,
Manilius and Cleomedes, who lived about 2000 years ago, and is one more
illustration of the great powers of observation and the general
acuteness of the natural philosophers of antiquity.

FOOTNOTES:

[Footnote 112: The time occupied by the Moon in passing through the
penumbra, before and after a lunar eclipse, will generally run to
about an hour for each passage. It will occasionally happen that the
Moon gets immersed in a penumbra but escapes the dark shadow. Such
an event will not be announced in the almanacs under the head of
"Eclipses."]

[Footnote 113: See p. 197 (_post_).]

[Footnote 114: The shadow is spoken of as being in the form of a
cone because it is necessarily such on account of the light-giving
disc of the Sun being so enormously larger in diameter than the
light-receiving sphere of the Moon. This idea can be pursued by any
reader with the aid of a lamp enclosed in a glass globe and an
opaque sphere such as a cricket ball.]

[Footnote 115: See p. 19 (_ante_).]

[Footnote 116: As to occultations see chap. xxi. (_post_).]

[Footnote 117: _Month. Not._, R.A.S., vo