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.


  1. #1 6EQUJ5

    The emission theory of vision isn’t yet dead. Notice how all the Terminators see by glowing red eyes? A lot of movie monsters are like that — glowing eyes. I wonder if they’re supposed to hear by having their ears buzz.

  2. #2 James Annan

    Hey, bats *do* use an emission method for “vision” – not buzzes but chirps though :-)

  3. #3 bob koepp

    Sorry not to be able to provide references. As for the craziness of the theroy, well, it helps to have an historically informed point of view. A “fire” that burned without light was an explanatory hypothesis in Greek science, especially medicine, and was probably about as reasonable at the time as the much better known hypothesis of atoms. And it was still being put forward during the early years of the scientific revolution in the 17th century.

  4. #4 John S. Wilkins

    Notice also that Superman in his “heat vision” uses the same notion. In fact it’s not so silly as we think from the post-Newton perspective. It was obvious that seeing is an action, so it follows that the actions must be initiated from the agent.

    I don’t have my references to hand, but I think you’ll find that Aristotle thought it was true.

  5. #5 guthrie

    If you can’t get anywhere by reference to the orignal texts, there’s bugger all else you can find out. We have comparatively few manuscripts from the period in question, entire books are only known of because someone copied a few paragraphs 300 years later into their own book, which has then been the only thing to survive so long.

    As for the emissions from eyes, the small problem is, how come humans can’t see in the dark?

    As for arabic science that prefigures Newton and Darwin, that has been, to some extent or another, known about for decades. In my reading about Alchemy, credit has been given to various Arabic investigators (I hesitate to call them scientists) for inventing new things and passing on the old Greek knowledge. However I do want some cross refences. The WIki entry for al-Haytham is positively fawning, but relies upon a number of source texts whose veracity I have not got a clue about. On the internet, I’ve run into a number of people of the “Arabs were genius’s and Islam rules” sort of people who would laud anyone from that period who looked intelligent, whether or not they actually are.

    Having said all that, some of the references are pretty solid, and what this does show is that there’s still a fair bit out there we do not know about, simply because of the difficulties of translation.

    However I have trouble with the Darwin comparison.
    ” In his Book of Animals, Jahith speculates on how environmental factors can affect the characteristics of species, forcing them to adapt and then pass on those new traits to future generations.”

    Which sounds to me nothing like “Darwinism”, more like the rival theory, whose name I have forgotten, in which animals adapt to the environment then pass the adaptations on to their offspring. SAying that prefigures DArwin is like saying Heraclitus prefigures Quantum theory.

  6. #6 ringo

    We tend to draw our mental models (and theories of mind) from the world around us. What kind of world, what kind of life, were the ancient Greeks living?

    If you blow on a fire, it flares up. Clearly some kind of addition is happening. We do this rarely – they did this daily. Dog and cat eyes light up in fire glow, and dim in darkness. We see this rarely – they saw this daily.

    [Errm yes. But human eyes don't. They saw that daily, too -W]

    Shadows and occlusions in vision also lend themselves to emission theory – again, we live in a relatively bright and unshadowed world. (Would a modern-living human have come up with the allegory of the cave?).

    What kinds of similar fallacies exist in the modern world? Can we even conceive otherwise?

  7. #7 Brian Schmidt

    Are you really going to make me think about Kant for two posts in a row?

    [No. AFAIK Kant is valueless. It was Aristotle -W]

    I think he drew his noumenon/phenomenon dialectic from Greek theory, and that even Greeks believed it to be metaphorical.

    Tangentially, I am curious what people thought about how bats navigated in complete darkness before sonar was discovered.

  8. #8 guthrie

    Ringo, speaking as someone who has spent a fair bit of time in fields with fires and candles and suchlike, I cannot see how shadows would support emission theory, given that the emission is clearly from the fire or oil lamp, not the human eye.

  9. #9

    To be able to see something, it has to be line-of-sight (you should excuse the expression) from both a light source and your eye. This isn’t true of hearing – we can hear around corners. So why are hearing and sight different? Thus, the shadows issue. Think like a Greek.

  10. #10 ringo

    Oh, and they knew that the light from human eyes was different from the light from animal eyes – it was invisible to humans. (Maybe it had to be, to keep us from dazzling ourselves).