That was my starting point, anyway. And I’ll aim to get back to it soonish. But I got sidetracked by the emission theory of vision, an idea so stupid that only a greek philosopher could possibly have thought it up, much less believed it.
I’d really like to understand whether anyone actualy believed this nonsense, or if it was just a metaphor. The wiki article is sourceless, and poking around the net didn’t really throw up much of use. Google books provided me with some of Johanssen on “Aristotle on the sense organs”, which makes it clear by quotation that Empedocles thought Aphrodite had made the eye somewhat like a lantern, with fire inside (and you thought climate septics were silly). However E says nothing direct about seeing. Plato says something about emission theory in the Timaeus and as usual is wrong; “He has no notion of trying an experiment and is hardly capable of observing the curiosities of nature which are ‘tumbling out at his feet,’ or of interpreting even the most obvious of them” said Jowett. Euclid and Ptolemy apparently believed it too. Weird.
Does anyone have usuable references for this stuff?
OK, so to pull some interesting stuff out of the comments:
A “fire” that burned without light was an explanatory hypothesis in Greek science – I partly agree. It was a hypothesis. It wasn’t explanatory, though, because it explained nothing: no useful lines of inquiry flowed from it, obviously enough, because it was wrong (it wasn’t even a fruitful error). It could easily be refuted by simple examination of an eye.
bats *do* use an emission method for “vision” – good point, though I think one that the Greeks were not aware of. But this immeadiately brings up the obvious problem: Hyopthesis: we/bats “see” by emission. Prediction: we/bats can “see” in the dark. Observation: we can’t. Bats can. Now this is so blindingly (ahem) obvious that even the philosophers noticed this bijou problemette with their theory. The answer, at least for Aristotle (this from memory, and since, as I think you can tell, I think this is all a pile of dingos kidneys, I may have remembered inaccurately by virtue of not wanting to give this tosh brainroom) was that the rays from the eye in some way mingled with the light from the sun, and thereby created vision. Whereas at night they mingled with inimical darkness as were thus extinguished. In which case, why not do away with the internal fire entirely? Answer, I think, is…
all the Terminators see by glowing red eyes? A lot of movie monsters are like that — glowing eyes – or, to put it another way, vision is “clearly” an intentful activity (errm, even though it isn’t) so its obviously necessary that we initiate it somehow. And to follow up I wonder if they’re supposed to hear by having their ears buzz. Funny how there was no apparent need to make hearing occur by emission.
The WIki entry for al-Haytham is positively fawning… I’m coming to that.