Plutarch De Defectu Oraculorum 2

[2] Yet a short time before the Pythian games, which were held when Callistratus ¹ was in office in our own day, it happened that two revered men coming from opposite ends of the inhabited earth met together at Delphi, Demetrius ² the grammarian journeying homeward from Britain to Tarsus, and Cleombrotus of Sparta, who had made many excursions in Egypt and about the land of the Cave-dwellers, and had sailed beyond the Persian Gulf; his journevings were not for business, but he was fond of seeing things and of acquiring knowledge; he had wealth enough, and felt that it was not of any great moment to have more than enough, and so he employed his leisure for such purposes; he was getting together a history to serve as a basis for a philosophy that had as its end and aim theology, as he himself named it. He had recently been at the shrine of Ammon, and it was plain that he was not particularly impressed by most of the things there, but in regard to the everburning lamp he related a story told by the priests which deserves special consideration; it is that the lamp consumes less and less oil each year, and they hold that this is a proof of a disparity in the years, which all the time is making one year shorter in duration than its predecessor; for it is reasonable that in less duration of time the amount consumed should be less.