historians, and for information about the Chinese we rely upon the
researches of travellers and missionaries in comparatively recent
times. The testimony of the Greek writers has fortunately been
confirmed, and we now have in addition a mass of facts translated from
the original sculptures, papyri, and inscribed bricks, dating back
thousands of years.

In attempting to appraise the efforts of the beginners we must
remember that it was natural to look upon the earth (as all the first
astronomers did) as a circular plane, surrounded and bounded by the
heaven, which was a solid vault, or hemisphere, with its concavity
turned downwards. The stars seemed to be fixed on this vault; the
moon, and later the planets, were seen to crawl over it. It was a
great step to look on the vault as a hollow sphere carrying the sun
too. It must have been difficult to believe that at midday the stars
are shining as brightly in the blue sky as they do at night. It must
have been difficult to explain how the sun, having set in the west,
could get back to rise in the east without being seen _if_ it was
always the same sun. It was a great step to suppose the earth to be
spherical, and to ascribe the diurnal motions to its rotation.
Probably the greatest step ever made in astronomical theory was the
placing of the sun, moon, and planets at different distances from the
earth instead of having them stuck on the vault of heaven. It was a
transition from "flatland" to a space of three dimensions.

Great progress was made when systematic observations began, such as
following the motion of the moon and planets among the stars, and the
inferred motion of the sun among the stars, by observing their
_heliacal risings_--i.e., the times of year when a star
would first be seen to rise at sunrise, and when it could last be seen