Astronomy is a useful aid in discovering the Dates of ancient
Monuments. Thus, on the ceiling of a portico among the ruins of
Tentyris are the twelve signs of the Zodiac, placed according to the
apparent motion of the sun. According to this Zodiac, the summer
solstice is in Leo; from which it is easy to compute, by the precession
of the equinoxes of 50″·1 annually, that the Zodiac of Tentyris must
have been made 4000 years ago.
Mrs. Somerville relates that she once witnessed the ascertainment of
the date of a Papyrus by means of astronomy. The manuscript was found
in Egypt, in a mummy-case; and its antiquity was determined by the
configuration of the heavens at the time of its construction. It proved
to be a horoscope of the time of Ptolemy.
“THE CRYSTAL VAULT OF HEAVEN.”
This poetic designation dates back as far as the early period of
Anaximenes; but the first clearly defined signification of the idea on
which the term is based occurs in Empedocles. This philosopher regarded
the heaven of the fixed stars as a solid mass, formed from the ether
which had been rendered crystalline by the action of fire.
In the Middle Ages, the fathers of the Church believed the firmament to
consist of from seven to ten glassy strata, incasing each other like
the different coatings of an onion. This supposition still keeps its
ground in some of the monasteries of southern Europe, where Humboldt
was greatly surprised to hear a venerable prelate express an opinion in
reference to the fall of aerolites at Aigle, that the bodies we called
meteoric stones with vitrified crusts were not portions of the fallen
stone itself, but simply fragments of the crystal vault shattered by it
in its fall.
Empedocles maintained that the fixed stars were riveted to the
crystal heavens; but that the planets were free and unconstrained.
It is difficult to conceive how, according to Plato in the _Timæus_,
the fixed stars, riveted as they are to solid spheres, could rotate
independently.
Among the ancient views, it may be mentioned that the equal distance
at which the stars remained, while the whole vault of heaven seemed to
move from east to west, had led to the idea of a firmament and a solid
crystal sphere, in which Anaximenes (who was probably not much later
than Pythagoras) had conjectured that the stars were riveted like nails.