set diminishes, and
its lustre begins gradually to decline. It sinks to invisibility, and is
forgotten by the great majority of mankind; but the capricious goddess
has only moved from one side of the sky to the other. Ere the sun rises,
the morning star will be seen in the east. Its splendour gradually
augments until it rivals the beauty of the evening star. Then again the
planet draws near to the sun, and remains lost to view for many months,
until the same cycle of changes recommences, after an interval of a year
and seven months.

When Venus is at its brightest it can be easily seen in broad daylight
with the unaided eye. This striking spectacle proclaims in an
unmistakable manner the unrivalled supremacy of this planet as compared
with its fellow-planets and with the fixed stars. Indeed, at this time
Venus is from forty to sixty times more brilliant than any stellar
object in the northern heavens.

The beautiful evening star is often such a very conspicuous object that
it may seem difficult at first to realise that the body is not
self-luminous. Yet it is impossible to doubt that the planet is really
only a dark globe, and to that extent resembles our own earth. The
brilliance of the planet is not so very much greater than that of the
earth on a sunshiny day. The splendour of Venus entirely arises from the
reflected light of the sun, in the manner already explained with respect
to the moon.

We cannot distinguish the characteristic crescent shape of the planet
with the unaided eye, which merely shows a brilliant point too small to
possess sensible form. This is to be explained on physiological grounds.
The optical contrivances in the eye form an image of the planet on the
retina which is necessarily very small. Even when Venus is nearest to
the earth the diameter of the planet subtends an angle not much more
than one minute of arc. On the delicate membrane a picture of Venus is
thus drawn about one six-thousandth part of an inch in diameter. Great
as may be the delicacy of the retina, it is not adequate to the
perception of form in a picture so minute. The nervous structure, which
has been described as the source of vision, forms too coarse a canvas
for the reception of the details of this tiny picture. Hence it is that
to the unaided eye the brilliant Venus appears merely as a bright spot.
Ordinary vision cannot tell what shape it has; still less can it reveal
the true beauty of the crescent.

If the diameter