Episode 052 - More on Light, Vision, and Reflections
Date: 01/11/21
Link: https://www.epicureanfriends.com/thread/1822-episode-fifty-two-more-on-light-vision-and-reflections/
Summary
Section titled “Summary”Elaine reads lines 230–323 of Book Four, covering the argument that touch and sight must share a common cause (the quadrangular shape argument); the theory that images tell us distance by pushing air before them to the eye; why images in a mirror appear behind the surface (the “double error” / double interval of air); left-right reversal explained by the clay mask analogy; multiple-mirror image chaining; and the equal-angles law of reflection.
Discussion ranges from Martin’s explanation of the “double air” (the image must travel eye-to-mirror and back, traversing the air interval twice), to Elaine’s observation about stereognosis and how babies use their mouths to build correlations between tactile and visual shape perception. A DeWitt passage (p. 204) is read contrasting Plato’s “eye-beam” theory, Democritus’s air-pulsation model, and Epicurus’s extremely filmy idol theory. Cassius previews a key line from just down the page that will anchor the whole epistemological discussion: the eyes are not to be blamed for what the mind fails to conclude — the eyes report where light and shadow are; the mind does the reasoning. The episode closes with a short discussion of whether color could in principle be detected by touch.
Transcript
Section titled “Transcript”Cassius: Welcome to Episode 52 of Lucretius Today. I’m your host, Cassius, and together with my panelists from the EpicureanFriends.com Forum, we’ll walk you through the six books of Lucretius’ poem and discuss how Epicurean philosophy can apply to you today. Be aware that none of us are professional philosophers and everyone here is a self-taught Epicurean. We encourage you to study Epicurus for yourself, and we suggest the best place to start is the book Epicurus and His Philosophy by Canadian professor Norman DeWitt. For anyone who is not familiar with our podcast, please check back to Episode 1 for a discussion of our goals and our ground rules. If you have any questions about that, please be sure to contact us at EpicureanFriends.com for more information. In today’s episode, we’re in Book 4 of the poem and we start with Latin text 230 and go to approximately 323. Now let’s join the discussion with Elaine reading today’s text.
Elaine: Besides, since any figure we feel with our hands in the dark we know to be the same we foresaw by day, and in the clearest light, the touch and sight must needs be moved by the same cause. And therefore, if we feel a quadrangular figure and distinguish its shape in the dark, what can present that shape to us in the light but its quadrangular image? The cause, therefore, of our sight must arise from the images; nor indeed can we distinguish anything without them.
Now these images I’m speaking of are carried about every way and are thrown off and scattered on all sides. And therefore it is, since with our eyes alone we are able to see, that whichever way we turn our eyes, the objects strike upon them in their proper form and color. The image likewise is the cause that we discover and takes care to satisfy us at what distance bodies are from us. For as soon as it is emitted, it instantly thrusts forward and drives in the air that is placed between itself and the sight. This stream of air then glides to the eye, and as it were, grates gently upon the ball, and so passes through. Hence it is that we perceive how far things are distant from our sight. For the more air there is that is driven before the image, and the longer the stream of it that rubs upon the ball, the longer the interval of space between the object and the eye must be allowed to be. All this is done with the utmost celerity, for we see what the object is and know its distance in the same instant.
Nor are we to think it at all strange in this case that the objects may be perfectly seen, and yet the images that singly strike the eye cannot themselves be discovered. For when the wind blows gently upon us, and its sharp cold pierces our bodies, we cannot discover it, nor can we distinguish the several particles of wind or cold that so affect us. But we are sensible of their whole strength together. We perceive their blows laid upon our bodies, as if something were beating us, and made us feel the effects of its outward force upon us. And so when we strike a stone with our fingers, we touch the surface and outmost color of the stone, but then we feel nothing of the color or surface by our touch. We perceive no more than the hardness of the stone that lies within.
And now learn why the image is always seen beyond the glass, for it certainly appears at a remote distance from us. For instance, when you are placed in an inner room and things are seen at a distance from you when the door is open, and it gives you a clear prospect and allows you plainly to discover any object without — your sight in this case is formed, as I may say, by a double air. The air that lies within the door is the first, then the door itself is the second, then the interval between, and then the light without that rubs gently upon the eye. And at length the object is discovered.
So when the image of the glass first flies off as it makes a passage to our sight, it strikes forward and drives in the air that lies between itself and the eye, so that we feel all this interjacent air before we see anything of the glass. But when we discover the glass, the image that is emitted from us instantly flies to us, and being reflected and sent back, returns again to our sight, and forces the air that is before it, which is the reason that we perceive this interjacent air before the image that is seen by us. Now when two airs are driven — the image of the glass forcing on one, the image reflected another — the interval must of necessity be more extended and even doubled. Hence it is that images appear not in the surface of the glass, but beyond it.
And therefore we are not to wonder at all that the images of things are reflected to our sight from the surface of the smooth glass by means of a double interval, because it appears plainly that they are so. But more — that the part of the body that is the right side appears in the glass to be the left — because the image, when it strikes upon the surface of the glass, is not reflected again unchanged, but is turned a different way about. For instance, take a mask made of clay while it is dry, and dash it against a pillar or beam. If it preserves its figure entire and appears inverted, so that the face fills up the hollow, the event will be that the right eye will now be the left, and the left the right.
And then it may be contrived that the image shall pass from one glass into another, so that five or six images shall be reflected at once, and objects that are placed backwards in the inward part of the house, let them be ever so much out of sight and the turnings ever so crooked, be drawn out through the winding passages and by the placing of so many glasses be perfectly discovered. The image may be so transferred from one glass into another that it will change its left into its right, but when it is again reflected from the second glass into the third it will resume its left part again, and will continue to change in the same manner as it passes into all the glasses that follow. But in glasses joined together in the convex figure of a pillar, the side of the image reflected is returned so that the right part of the image answers to the right of the object — either because the image being transferred from one glass into another is reflected twice, or because the image when it comes to us is turned about, in that the face is turned about as it passes backwards — we learn from the figure of the glass.
Besides, you would believe that the image moves with us and attends all our steps and imitates our gestures, because when you retire from any part of the glass, the image cannot be reflected from that part. For nature ordains that all images that are emitted from bodies be returned and reflected by equal angles.
Cassius: Elaine, thank you for reading 100 lines of the driest material we’ve probably ever read in the book. If someone were to pick up this book at this passage and start reading, they would throw it down as some of the most useless things they could possibly have read. So it’s going to be up to us to get through this and relate it to reality.
Elaine: It’s funny to me that you have that reaction. Why? Tell me your reaction.
Cassius: Well, it’s more of an attempt to understand what he’s seeing and to come up with explanations — which are not right. But it’s fascinating the way his mind works. I don’t find it drier than the other parts.
Martin: Well — I think I lost the double air. The double air. That was interesting. Do you know what he means by that?
Cassius: You know — this is when you look at the mirror. So you have the air between…
Martin: The air counts twice — from between your eye to the mirror, and back to the eye. That’s why it’s a double air. Exactly. So, the theory comes up that the light is pushing the air, and from the pressure of the air, we can sense the distance. That is nonsense. But it’s creative, creative nonsense. For the time, it probably made a lot of sense.
Cassius: Yeah.
Martin: But the detail of the observation is again striking. That tiny detail is added, and he tries to put it in the context of the theory, which somehow makes sense in this primitive framework.
Elaine: Isn’t that amazing, right? Right. I had a thought about this very first passage where he’s talking about being able to distinguish a shape without looking at it, which is a specific type of neurologic ability. Some people can lose that — they’ll reach into a bag and feel an object, and they’re not able to understand its shape with their hands. Isn’t there a similar thing with people who are blind, or who regain their sight, and they can’t recognize images?
Martin: Yes. The shapes and how to interpret 3D.
Elaine: So I have a pediatric perspective on this. You know that stage that young babies go through where they want to put everything in their mouths? If you watch them real closely, they will hold it right in front of their face and look at it, put it in their mouth and mouth it, then look at it and mouth it again. Parents think they’re teething, but the hypothesis of what they’re doing may be forming a correlation between vision, 3D vision and shape — because the mouth, not only the hands, is a great way to feel the shapes of objects in detail. We have a lot of sensory nerve endings in the mouth. So they put this square block in their mouth and feel all the edges with their tongue, then take it out and look at it. They’re building these connections so they really understand what it is they’re seeing because they’ve felt it. I just think that’s fascinating.
Cassius: Well, I agree that it’s fascinating too, despite what I said. You know, we’ll keep going then, Elaine. Before I pull back to some of the more general comments I wanted to make today, let’s continue with the details here that you think are particularly interesting.
Elaine: Well, all this about the mirrors — I agree with Martin. He really had so many observations and was trying to come up with a way to put them together, even though it was wrong. It’s just fascinating. But when he starts talking about all the different mirrors — I have a good friend, one of my closest friends, who has the most hilarious sense of humor with her decorating. She has a beautiful house with all sorts of interesting objects, but she also has these little humor bits, and she got this idea to decorate her fairly small guest bathroom with mirrors. It has large, small, ornate mirrors. I’ve never seen so many mirrors in one little room. And so your image in the bathroom is everywhere, being reflected from one mirror to another. That’s a really interesting experience. And I thought about her bathroom when he was talking about all these mirrors and things being reflected between them. Decorating idea for any of you who want to play around.
Cassius: Will the text from this section be plastered on the wall in that room?
Elaine: Yes, it should be.
Cassius: Oh, that’s a great idea. Well, I have to admit that I’ve always found fascinating the effect of bouncing things back and forth — I think about it more in terms of a camera aimed at a television screen, but the apparently like-infinite regress of images bouncing back and forth. You can do that with mirrors too, right?
Elaine: You know, when you point the camera at the screen and you start seeing yourself in ever-smaller images.
Martin: We had in our bathroom two opposite mirrors, so you could see practically an infinite number of your reflections — getting smaller and farther away. Not really infinite, but not a limited series.
Cassius: It’s humorous to me. I wonder if Lucretius thought it was kind of funny.
Elaine: Certainly the way he describes it sounds playful. Yeah.
Cassius: Now is your feeling of dryness different a little bit?
Elaine: A little bit. If I were having to explain this to somebody who just started on this podcast, I’d have to relate it back to something more general. But that’s part of the deal — you just can’t reduce everything to a high-level abstraction. You’ve got to deal with details and explanations for why you come up with your conclusions. And this is one of those many details he works through.
Cassius: All right. Well, I can begin to transition. Once we get to next week, we’ll start working out of this. But one of the things I posted as a separate post — on the EpicureanFriends.com forum and on the Facebook page — is that just down the page, he starts talking about shadows, and he makes this statement that I think is part of what brings it all home. He says: “But in this case we are not in the least to allow that the eyes are deceived. It is their business to discover only where the light and the shade are, but to determine nothing whether the light be the same or the shadow be the same that moves one place to another or whether it be as we explained above. It is the office of the mind and judgment to distinguish this. For the eyes can know nothing of the nature of things, and therefore you’re not to impute to them the failures of the mind.”
So you see — you can have different theories about how these reflections work, and the eyes aren’t going to give you the answer as to how things work. They’re going to give you observations from which you can construct an understanding, but the eyes don’t do the understanding. For example, the very last statement that Elaine read today — “nature ordains that all images that are emitted from bodies should be returned and reflected by equal angles” — that is a conclusion. And it may be right or it may be wrong, but only the eyes can tell us whether it’s right or wrong.
Elaine: Okay, so my thoughts — these days I don’t really conceive of the nervous system as being so clearly separable. Obviously the retina is not the prefrontal cortex, but the peripheral nervous system and the sense organs — without those, the brain wouldn’t have anything to work with. And you can make the same kinds of distinctions within the brain itself too: you could have a stroke and lose your mathematical abilities, or you can understand language but can’t produce it. So the functions of the brain are as specific as the distinction between brain and eye. It gives you options for how you want to divide the nervous system and talk about it.
So in one way, you could talk about the sense of sight as being the combination of the eye, the optic nerve, and the visual cortex. And then how we interpret it is additional functions of the brain. But the visual cortex does some of that automatically, because of recognition and the ability to integrate vision with our other senses like our tactile sense. So it’s a little more complicated than the way it’s presented here. But it’s not wrong to say one part of the nervous system can’t do the job of the entire nervous system, and that our decision to understand things requires multiple parts of the nervous system, not just one — and definitely not just an eyeball.
Cassius: Martin or Charles, anything right now?
Martin: No.
Cassius: Okay. Well, since Elaine just mentioned the eyeball, let me pull out a section from the DeWitt book that I think helps put some of this in perspective. I’m going to read a paragraph or two from page 204, under a subsection entitled “Vision.” DeWitt says:
“In his explanation of vision, Epicurus sets himself in opposition to both Democritus and Plato. The latter had thought of the eyes as discharging little beams of light which, being homogeneous with the light of day, were capable of revealing the shapes and colors of external objects, conveying the impressions of them back to the consciousness of the observer. The essential part of this theory is the homogeneity of the beam extending between eye and object, which ensures that red will be reported red and square square. In darkness, homogeneity is lacking and hence vision also.”
And then DeWitt says: “According to Democritus, the intervening air served as a medium in vision, being shaped in images by the pulsation of the atoms in an object. These images cause the sensation by falling upon the soft and moist surface of the pupil as upon a mirror. If the adoption of the air as a medium was occasioned by fear that atoms of solid bodies might wound the delicate surface of the eye, we may well understand why Epicurus in rejecting his master’s teaching dwells so positively upon the extreme filminess of the idols which he represents all bodies as discharging. At the same time that he overcomes this difficulty, he gives the opinion that the stream of idols thrown off by the object itself accounts more satisfactorily for the precision of the image impressed upon the eye as if by an engraved seal.”
So one of the background contexts we’re dealing with here is that Democritus and Plato had very different positions on how vision works.
Elaine: I mean, I think it was interesting, but I’m not sure what else to say about it. Maybe this is just a shorter podcast, despite the length of the passage.
Cassius: Probably, Elaine — that’s what I’ll do. I’ll bring the podcast to a close pretty quickly here today on these points, because I believe as soon as next week we’re into the application of this information. Then it gets back to the question of when can vision be trusted and when can it not be trusted, how do we check our observations against other observations, and so forth. But right now we’re in the middle of the details, and the application isn’t there yet.
Elaine: The only other thing I noticed — in the second paragraph: “And so when we strike a stone with our fingers, we touch the surface and outmost color of the stone, but then we feel nothing of the color or surface by our touch. We perceive no more than the hardness of the stone that lies within.” Is that “feel nothing of the color” — meaning we don’t feel the color? Because of course we do feel texture.
Cassius: I’m thinking that he means we don’t feel the color specifically. So I would like to say that our anatomy correlates the feeling of the shape of an object with our vision. And some people who are blind have trained themselves by a form of echolocation — so they can hear a sound bouncing off objects and understand their shapes. So there’s not really a reason we can’t feel color because light has different wavelengths coming off an object. So there could be an organism with a nervous system that could detect differences between wavelengths of light and correlate that with visual color. We just don’t have that ability. But I can’t think of any reason why it would be physiologically ruled out.
Elaine: Why it should be physiologically ruled out that we cannot touch color? Yeah. So far as I know, humans don’t have that ability. But I don’t think it would be a fantastical thing to imagine there could be an organism that could develop that skill — like bats and sonar. It seems possible to me that there could be a tactile sense so refined it could detect differences in wavelengths of light. I don’t know that any such thing exists, but I wouldn’t think it’s beyond possibility that it could evolve.
Martin: I think you’re right, Elaine. But when I was a kid, I was convinced I could tell the difference between differently colored objects of the same shape with my eyes closed. And then my dad, the physicist, said: no, you can’t. What you can do is, by experience, if there is a difference in texture — not directly the color, but if the pigments leave the surface a different texture — that one you might be able to sense, and then you correlate it. Once you know this and you’ve trained for it, you feel like you can sense the color.
Cassius: At an atomic or very small level, does the wavelength that’s reflected off of something have to do with the shape of the surface?
Martin: No, no — this is a molecular thing.
Cassius: All right. Well, Charles, what else do you have for today?
Charles: It’s just one of those sections again where I prefer to listen.
Cassius: Okay. Hearing nothing further from anyone about the text today, I’m about to declare us finished for the day unless anybody has any final thoughts.
Martin: Not me.
Elaine: Not me either.
Cassius: Okay, very good. All right, well we’ll get this podcast out and come back to discuss images further next week. Thanks everybody, close for the day then.
Elaine: Bye. Thanks and bye.