_stretching_, which is the conception implied in this name of the
instrument. This mythological _Bow_, as I explained, _Proc. Soc. Bibl.
Arch._, VI, 131, is the moon’s _crescent_, which during its course
through the sky is always turned towards the sun; so that a line at
right angles to the chord of the arc passes through the sun’s centre.
From this “very delicate observation,” as Arago calls it, the
Alexandrian astronomer Geminus infers that the moon derives its light
from the sun. The observation evidently had been made in Egypt some
thousands of years before Geminus, and explains why in several chapters
the sun is spoken of as shining in or from the moon.
See also _Proc. Soc. Bibl. Arch._, XVII, 37, on another form of the
myth.