omes between the earth and the sun, near the line
where the planes of their orbits cut each other by reason of their
inclination, the dark body of Mercury will be seen on the bright
surface of the sun. This is called a transit. If it goes across
the centre of the sun it may consume eight hours. It goes 100,000
miles an hour, and has 860,000 miles of disk to cross. The transit of
1818 occupied seven and a half hours. The transits for the remainder
of the century will occur:

November 7th 1881 | November 10th 1894
May 9th 1891 | November 4th 1901

VENUS.

Goddess of beauty; its sign [Symbol], a mirror.

DISTANCE FROM THE SUN, 66,750,000 MILES. DIAMETER, 7660 MILES.
ORBITAL VELOCITY, 1296 MILES PER MINUTE. AXIAL REVOLUTION, 23H.
21M. ORBITAL REVOLUTION, 224.7 DAYS.

This brilliant planet is often visible in the daytime. I was once
delighted by seeing Venus looking down, a little after mid-day
through the open space in the dome of the Pantheon at Rome. It
has never since seemed to me as if the home of all the gods was
deserted. Phoebus, Diana, Venus and the rest, thronged through
that open upper door at noon of night or day. Arago relates that
Bonaparte, upon repairing to Luxemburg when the Directory was about
to give him a _fete_, was much surprised at seeing the multitude
paying more attention to the heavens above the palace than to him
or his brilliant staff. Upon inquiry, he learned that these curious
persons were observing with astonishment a star which they supposed
to be that of the conqueror of Italy. The emperor himself was not
indifferent when [Page 140] his piercing eye caught the clear lustre
of Venus smiling upon him at mid-day.

This unusual brightness occurs when Venus is about five weeks before
or after her inferior conjunction, and also nearest overhead by
being north of the sun. This last circumstance occurs once in eight
years, and came on February 16th, 1878.

Venus may be as near the earth as 22,000,000 miles, and as far
away as 160,000,000. This variation of its distances from the earth
is obviously much greater than that of Mercury, and its consequent
apparent size much more changeable. Its greatest and least apparent
sizes are as ten and sixty-five (Fig. 53).

[Illustration: Fig. 53.--Phases of Venus, and Varions Apparent
Dimensions.]

When Copernicus announced the true theory of the solar system, he
said that if the inferior planets could be clearly seen they wou