400 B.C.; probably as early as 700 B.C.; in any case, not later than 475 B.C.
Before parting from the grotto on Cynthus, the students of ancient astronomy may be invited to consider a question which can scarcely fail to interest them. In the Revue archéologique of August, 1873, M. Burnouf intimated that "a series of astronomical considerations, supported by numerous texts, had led him to think that Delos had been a centre of very ancient observations, and had performed for the Ionians a part similar to that which afterwards belonged to the Acropolis of Athens." The solar character of Apollo was, he added, in favour of this view. This theory has been developed with great ingenuity by M. Lebégue. We have seen that the east end of the grotto—that which rests against Cynthus—was not completely closed. On an April morning a ray of the sun pierces the cavern and fills it in a moment. Apollo was supposed to spend the winter in Lycia, and to revisit Delos with the spring: we hear, too, of his Delian oracle being consulted in the morning. M. Lebégue suggests that the grotto may have been a station at which the process of the seasons was observed by noting the length and inclination of the sun's rays. Solstitial dials or gnomons were known from a remote age in Greece, which may have received them, through the Phoenicians, from Chaldaea. Referring to Odyssey, xv. 403,
νῆσός τις Συρίη κικλήσκεται, εἴ που ἀκούεις,
Ὀρτυγίης καθύπερθεν, ὅθι τροπαὶ ἠελίοιο,
