Lucretius Today Podcast Episode 052 – More on Light, Vision, and Reflections

Listen to “Episode 052 – More on Light, Vision, and Reflections” on Spreaker.

Welcome to Episode Fifty-Two of Lucretius Today.

I am 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.

In today’s episode, we read Latin Text 230-323

1743 Browne

Besides, since any figure we feel with our hands in the dark, we know to be the same we before saw 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 any thing without them.

Now these images I am 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 which way soever 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 removed from us, for as soon as it is emitted, it instantly thrusts forward, and drives on 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 instance. 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 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 out most 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 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 is placed in the middle between, and then the light without that rubs gently upon the eye, this is the other air; 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 on 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 it, 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 is seen by us. Now when two airs are driven (the image of the glass forcing on one, and the image reflected another) the interval must of necessity be more extended, and even doubled. Hence it is that the images appears not in the surface of the glass, but beyond it, and therefore we are not to wonder at all that the images of things reflected to our sight, from the surface of a smooth glass, by means of a double air, 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, before it is dry, and dash it against a pillar or beam; if it preserves its figure entire, and appears inverted only 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, they may 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 or thing seen; either because the image, being transferred from one glass into another, is reflected twice, or that the image, when it comes to us, is turned about; for 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 should be returned and reflected by equal angles.