Right then. The moon and the sun are linked as the eyes of a god in various places in Egyptian myth - I'll stick a bunch of notes behind the cut - but if my rummagings are correct, how the right eye, the solar Eye of Re, the ferocious goddess, overlaps with the left eye, the lunar Eye of Horus, is this: Thoth brings them both back.
I was familiar with two stories involving Thoth and an eye - the myth of the Distant Goddess, in which the Eye of Re decamps to Nubia in a huff, and Thoth (or Onuris, or Shu) is dispatched to get her back; and the healing of Horus' eye after Set's assault.
What I didn't know is that there's also a myth in which Horus's eye wanders off and Thoth returns it to him:
The eye of Horus sprang up as he fell on yonder side of the Winding Watercourse, to protect itself against (or, free itself from) Set.
Thot saw it on yonder side of the Winding Watercourse.
The eye of Horus sprang up on yonder side of the Winding Watercourse, and fell upon the wing of Thot on yonder side of the Winding Watercourse.
O ye gods, ye who ferry over on the wing of Thot to yonder side of the Winding Watercourse, to the eastern side of heaven, to speak with Set about that eye of Horus, may N. ferry over with you on the wing of Thot to yonder side of the Winding Watercourse, to the eastern side of heaven, that he, N., may speak with Set about that eye of Horus.
- Pyramid Texts 594-596
It'd make a great animated cartoon - Horus' eye either leaping out of his face (or perhaps off Set's forehead) and Thoth spotting it in time to catch it and fly it back to its owner. (Hmmm. I wonder if this is an image of the changeable moon travelling through the sky.)
Various other bits of the PT touch on the same story. Patrick Boylan discusses all this in a footnote:
"The legend of the flight and return of the eye is obviously similar in many respects to the legends of the Destroying Eye of Re, of the angry eye which becomes the serpent on the diadem of the sun-god, of Onuris who fetched the divine lioness from the eastern desert, and of Hathor of Byblos. All these legends are intricately interwoven - so much so, indeed, that it is often difficult to decide to which of them a particular feature or motif primitively belongs. Thoth is certainly associated primitively with the astral legend of the moon-eye that vanished and was found again. The primitive astral myth contains no suggestion of an angry eye of Horus. Thoth's function as pacifier of the eye is connected with the more reflective legends of the Eye as Serpent on the crown of Horus (in which Sechmet appears as the Eye in her form nsr.t, and Thoth is the shtp nsr.t). (p 32, fn 1)
It's a bit slack to just quote chunks of Boylan, but I'm knackered and he explains it so simply:
"The name of [Onuris] Ini hri.t, 'He who brings the one who was far away', refers probably to the bringing to Egypt from the mountain lands of the eastern deserts of a goddess in leonine form who was forced or induced to leave her desert home by an ancient battle-god in lion or falcon form. This ancient god was Horus the warrior-god who, because he brought to Egypt the stranger goddess, received the epithet Ini hri.t (Onuris) - 'He that fetches her that was far away'. Later this Hri.t came to be identified with the wd3.t and Ini hri.t was explained as 'He that brings the Eye that was far away'. Thus, the name of Onuris came to be written (as Thoth's could be, and sometimes was, written) as a deity carrying the wd3.t. (p 35)
And as a footnote to that lot:
"In some cases, of course, Thoth brings back to Horus (or Re) the right eye, or the Sun. This activity seems to be secondary or borrowed in the legends of the sun-god Re: it is based on his more primitive activity in connection with the moon." (p 35 fn 1)
So there you go - multiple versions of basically the same story, the eye leaving and being returned, with slippage between just which eye is doing the round trip.
( More notes )__
Andrews, Carol. "The Boar, the Ram-Headed Crocodile and the Lunar Fly". in
Studies in Egyptian Antiquities: A Tribute to T.G.H. James (Occasional paper 123). London, British Museum, 1999. pp. 79 - 81.
Boylan, Patrick.
Thoth, the Hermes of Egypt. Chicago, Ares Publishers, 1987. (A reprint of
this, I believe.)
Darnell, J. C. 1997. The Apotropaic Goddess in the Eye.
Studien zur Altägyptischen Kultur 24, pp 35-48.
Troy, Lana. "Mut Enthroned". in van Dijk, J. (ed.),
Essays on Ancient Egypt in Honour of Herman te Velde, Groningen, 1997, pp.301-315.
Willems, Harco.
The coffin of Heqata (Cairo JdE 36418): a case study of Egyptian funerary culture of the early Middle Kingdom. Leuven, Uitgeverij Peeters en Departement Oriëntalistiek, 1996.