Philosophical Letters: or, modest Reflections upon some Opinions in Natural Philosophy. Duchess of Margaret Cavendish Newcastle

rational and sensitive perception, sight and knowledg. The same with Ecchoes; for the air patterns out the copy of the sound, and then the sensitive corporeal motions in the ear pattern again this copy from the air, and so do make the perception and sense of hearing. You may ask me, Madam, if it be so, that the glass and the air copy out the figure of the face and of sound, whether the Glass may be said to see and the Air to speak? I answer, I cannot tell that; for though I say, that the air repeats the words, and the glass represents the face, yet I cannot guess what their perceptions are, onely this I may say, that the air hath an elemental, and the glass a mineral, but not an animal perception. But if these figures were made by the pressures of several objects or parts, and by reaction, there could not be such variety as there is, for they could but act by one sort of motion: Likewise is it improbable, that sounds, words or voices, should like a company of Wild-Geese fly in the air, and so enter into the ears of the hearers, as they into their nests: Neither can I conceive, how in this manner a word can enter so many ears, that is, be divided into every ear, and yet strike every ear with an undivided vocal sound; You will say, as a small fire doth heat and warm all those that stand by; for the heat issues from the fire, as the light from the Sun. I answer, all what issues and hath motion, hath a Body, and yet most learned men deny that sound, light and heat have bodies: But if they grant of light that it has a body, they say it moves and presses the air, and the air the eye, and so of heat; which if so, then the air must not move to any other motion but light, and onely to one sort of light, as the Suns light; for if it did move in any other motion, it would disturb the light; for if a Bird did but fly in the air, it would give all the region of air another motion, and so put out, or alter the light, or at least disturb it; and wind would make a great disturbance in it. Besides, if one body did give another body motion, it must needs give it also substance, for motion is either something or nothing, body or no body, substance or no substance; if nothing, it cannot enter into another body; if something, it must lessen the bulk of the body it quits, and increase the bulk of the body it enters, and so the Sun and Fire with giving light and heat, would become less, for they cannot both give and keep at once, for this is as impossible, as for a man to give to another creature his human Nature, and yet to keep it still. Wherefore my opinion is for heat, that when many men stand round about a fire, and are heated and warmed by it, the fire doth not give them any thing, nor do they receive something from the fire, but the sensitive motions in their bodies pattern out the object of the fires heat, and so they become more or less hot according as their patterns are numerous or perfect; And as for air, it patterns out the light of the Sun, and the sensitive motions in the eyes of animals pattern out the light in the air. The like for Ecchoes, or any other sound, and for the figures which are presented in a Looking-glass. And thus millions of parts or creatures may make patterns of one or more objects, and the objects neither give nor loose any thing. And this I repeat here, that my meaning of Perception may be the better understood, which is the desire of,

      Madam,

      Your faithful Friend,

      and Servant.

XXV.

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      MADAM

      I perceive you are not fully satisfied with my former Letter concerning Eccho, and a figure presented in a Looking-glass; for you say, how is it possible, if Eccho consists in the ears patterning out of a voice or sound, but that it will make a confusion in all the parts of the air? My answer is, that I doe not say that Eccho is onely made by the patterning out of the voice or sound, but by repeating the same voice or sound, which repetition is named an Eccho, for millions of ears in animals may pattern out a voice or words, and yet never repeat them, and so may millions of parts of the air; wherefore Eccho doth not consist in the bare patterning out, but in the repetition of the same sound or words, which are pattern'd out; and so some parts of the air may at one and the same time pattern out a sound and not repeat it, and some may both pattern out, and repeat it, but some may neither pattern out, nor repeat it, and therefore the Repetition, not the bare Patterning out is called Eccho: Just as when two or more men do answer or mock each other, and repeat each others words, it is not necessary, if there were a thousand standers by, that they should all do the same. And as for the figure presented in a Looking-glass, I cannot conceive it to be made by pressure and reaction; for although there is both pressure and reaction in nature, and those very frequent amongst natures Parts, yet they do neither make perception nor production, although both pressure and reaction are made by corporeal self-motions; Wherefore the figure presented in a Looking-glass, or any other smooth glassie body, is, in my opinion, onely made by the motions of the Looking-glass, which do both pattern out, and present the figure of an external object in the Glass: But you will say, why do not the motions of other bodies pattern out, and present the figures of external objects, as well as smooth glassie bodies do? I answer, they may pattern out external objects, for any thing I know; but the reason that their figures are not presented to our eyes, lies partly in the presenting subject it self, partly in our sight; for it is observed, that two things are chiefly required in a subject that will present the figure of an external object; first it must be smooth, even and glassie, next it must not be transparent: the first is manifest by experience; for the subject being rough and uneven, will never be able to present such a figure; as for example, A piece of steel rough and unpolished, although it may perhaps pattern out the figure of an external object, yet it will never present its figure, but as soon as it is polished, and made smooth and glassie, the figure is presently perceived. But this is to be observed, that smooth and glassie bodies do not always pattern out exterior objects exactly, but some better, some worse; like as Painters have not all the same ingenuity; neither do all eyes pattern out all objects exactly; which proves that the perception of sight is not made by pressure and reaction, otherwise there would be no difference, but all eyes would see alike. Next I say, it is observed, that the subject which will present the figure of an external object, must not be transparent; the reason is, that the figure of Light being a substance of a piercing and penetrating quality, hath more force on transparent, then on other solid dark bodies, and so disturbs the figure of an external object pattern'd out in a transparent body, and quite over-masters it. But you will say, you have found by experience, that if you hold a burning Candle before a Transparent-glass, although it be in an open Sun-light, yet the figure of light and flame of the Candle will clearly be seen in the Glass. I answer, that it is an other thing with the figure of Candle-light, then of a duskish or dark body; for a Candle-light, though it is not of the same sort as the Suns light, yet it is of the same nature and quality, and therefore the Candle-light doth resist and oppose the light of the Sun, so that it cannot have so much power over it, as over the figures of other bodies patterned out and presented in Transparent-glass. Lastly, I say, that the fault oftentimes lies in the perceptive motions of our sight, which is evident by a plain and Concave-glass; for in a plain Looking-glass, the further you go from it, the more your figure presented in the glass seems to draw backward; and in a Concave-glass, the nearer you go to it, the more seems your figure to come forth: which effects are like as an house or tree appears to a Traveller; for, as the man moves from the house or tree, so the house or tree seems to move from the man; or like one that sails upon a Ship, who imagines that the Ship stands still, and the Land moves; when as yet it is the Man and the Ship that moves, and not the House, or Tree, or the Land; so when a Man turns round in a quick motion, or when his head is dizzie, he imagines the room or place, where he is, turns round. Wherefore it is the Inherent Perceptive motions in the Eye, and not the motions in the Looking-glass, which cause these effects. And as for several figures that are presented in one glass, it is absurd to imagine that so many several figures made by so many several motions should touch the eye; certainly this would make such a disturbance, if all figures were to enter or but to touch the eye, as the eye would not perceive any of them, at lead not distinctly; Wherefore it is most probable that the glass patterns out those figures, and the sensitive corporeal motions in the eye take again a pattern from those figures patterned out by the glass, and so make copies of copies; but the reason why several figures are presented in one glass in several places, is, that two perfect figures cannot be in one point, nor made by one motion, but by several corporeal motions. Concerning a Looking-glass, made in the form or shape of a Cylinder, why it represents the figure of an external object in an other shape and posture