constructed on the principle just set forth was known to and used by the Greek astronomers of antiquity under the name of a _Sciotheron_ or shadow-taker. Sometimes, and perhaps more properly, it was called a _Heliotropion_, that is, an instrument designed to indicate the turning of the Sun at the Tropics.[28] This, be it remembered, was information needed by the ancients for the correct regulation of the seasons of the year, and of special service to the Jews whose greater festivals were fixed in connection with the seasons. There is reason to believe that instruments of this character were of early invention, going back perhaps to the times of Homer, for we find a passage in the _Odyssey_, (xv. 403) as follows:— “Above Ortygia lies an isle of fame Far hence remote, and Syria [Syros] is the name; There curious eyes inscrib’d with wonder trace The Sun’s diurnal and his summer race.” Pope’s rendering of this passage fails, however, to bring out the salient idea involved. Butcher and Lang translate the passage thus:—“There is a certain isle called Syria, if haply thou hast heard tell of it, over above Ortygia, and there are the turning-places of the Sun.” Merry[29] calls these island names mere “inventions of the poet.” It seems to me a great question whether Homer’s words really support the statement I have made just before quoting it. Diogenes Laërtius refers to this same instrument when he speaks of the Heliotropion preserved in the Island of Syra.[30] According to Laërtius, Anaximander[31] was the first Greek to use gnomons, which he placed on the Sciothera of Lacedæmon, for the express purpose of indicating the Tropics and Equinoxes. These Sciothera were pyramidal in form.