other places.

The existence of Mercury was certainly quite a familiar fact in the time
of Copernicus, and therefore we must look to some earlier epoch for its
discovery. In the scanty astronomical literature of the Middle Ages we
find occasional references to the existence of this object. We can trace
observations of Mercury through remote centuries to the commencement of
our era. Records from dates still earlier are not wanting, until at
length we come on an observation which has descended to us for more than
2,000 years, having been made in the year 265 before the Christian era.
It is not pretended, however, that this observation records the
_discovery_ of the planet. Earlier still we find the chief of the
astronomers at Nineveh alluding to Mercury in a report which he made to
Assurbanipal, the King of Assyria. It does not appear in the least
degree likely that the discovery was even then a recent one. It may have
been that the planet was independently discovered in two or more
localities, but all records of such discoveries are totally wanting; and
we are ignorant alike of the names of the discoverers, of the nations to
which they belonged, and of the epochs at which they lived.

Although this discovery is of such vast antiquity, although it was made
before correct notions were entertained as to the true system of the
universe, and, it is needless to add, long before the invention of the
telescope, yet it must not be assumed that the detection of Mercury was
by any means a simple or obvious matter. This will be manifest when we
try to conceive the manner in which the discovery must probably have
been made.

Some primaeval astronomer, long familiar with the heavens, had learned to
recognise the various stars and constellations. Experience had impressed
upon him the permanence of these objects; he had seen that Sirius
invariably appeared at the same seasons of the year, and he had noticed
how it was placed with regard to Orion and the other neighbouring
constellations. In the same manner each of the other bright stars was to
him a familiar object always to be found in a particular region of the
heavens. He saw how the stars rose and set in such a way, that though
each star appeared to move, yet the relative positions of the stars were
incapable of alteration. No doubt this ancient astronomer was acquainted
with Venus; he knew the evening star; he knew the morning star; and he
may have concluded that Venus was a body