sun. The only conceivable use of a fixed
instrument so placed would be to show the rise and fall of the shadow
from day to day, as the Sun on the meridian gradually rose higher
between mid-winter and mid-summer, or descended lower between mid-summer
and mid-winter, in passing of course through the winter and summer
solstices in turn. No simple motion of the Sun in its ordinary diurnal
progress would produce the effect described. On the other hand, it is
equally clear that the shadow cast by a gnomon properly adjusted at the
head of such a series of steps would travel upwards and downwards upon
the steps "with the Sun," from winter to summer and from summer to
winter, indicating at each noon the meridian altitude of the Sun from
day to day, the latitude of Jerusalem being 31 deg. 47', and the Sun's
altitude there on the shortest day being 34 deg. 41'. If the gnomon were
raised above the topmost step so as to bring the tip of the gnomon or
any aperture in it so much above the step as would be the equivalent of
2 deg. 54' or slightly more, then the top of the shadow of the gnomon (or a
spot of light passing through a hole in it) would, on the shortest day
of the year, fall just beyond the lowermost step. An instrument
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