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to our eyes, and that of a million of rays that rebound from any visible area of any body, perhaps the or
part coming to the eye, are enough to move the retina sufficiently to cause a sensation in the mind; will not find any great difficulty in the objections which are brought from the impenetrability of matter, and these rays ruffling and breaking one another in the medium which is full of them. As to what is said, that from one point we can see a great number of objects, that is no objection against the species, or visible appearances of bodies, being brought into the eye by the rays of light; for the bottom of the eye or retina, which, in regard of these rays, is the place of vision, is far from being a point. Nor is it true, that though the eye be in any one place, yet that the sight is performed in one point, i. e. that the rays that bring those visible species do all meet in a point; for they cause their distinct sensations, by striking on distinct parts of the retina, as is plain in optics; and the figure they paint there must be of some considerable bigness, since it takes up on the retina an area whose diameter is at least thirty seconds of a circle, whereof the circumference is in the retina, and the centre somewhere in the crystalline; as a little skill in optics will manifest to any one that considers, that few eyes can perceive an object less than thirty minutes of a circle, whereof the eye is the centre. And he that will but reflect on that seeming odd experiment of seeing only the two outward ones of three bits of paper stuck up against a wall, at about half a foot, or a foot one from another, without seeing the middle one at all, whilst his eye remains fixed in the same posture, must confess that vision is not made in a point, when it is plain, that looking with one eye there is always one part between the extremes of the area that we see, which is not seen at the same time that we perceive the extremes of it; though the looking with two eyes, or the quick turning of the axis of the eye to the part we would distinctly view, when we look but with one, does not let us take notice of it.
10. What I have here said I think sufficient to make
intelligible, how by material rays of light visible species may be brought into the eye, notwithstanding any of P. M.'s objections against so much of material causes as my hypothesis is concerned in. But when by this means an image is made on the retina, how we see it, I conceive no more than when I am told we see it in God. How we see it, is, I confess, what I understand not in the one or in the other, only it appears to me more difficult to conceive a distinct visible image in the uniform invariable essence of God, than in variously modifiable matter; but the manner how I see either, still escapes my comprehension. Impressions made on the retina by rays of light, I think I understand; and motions from thence continued to the brain may be conceived, and that these produce ideas in our minds, I am persuaded, but in a manner to me incomprehensible. This I can resolve only into the good pleasure of God, whose ways are past finding out. And, I think, I know it as well when I am told these are ideas that the motion of the animal spirits, by a law established by God, produces in me; as when I am told they are ideas I see in God. The ideas it is certain I have, and God both ways is the original cause of my having them; but the manner how I come by them, how it is that I perceive, I confess I understand not; though it be plain motion has to do in the producing of them and motion, so modified, is appointed to be the cause of our having them; as appears by the curious and artificial structure of the eye, accommodated to all the rules of refraction and dioptrics, that so visible objects might be exactly and regularly painted on the bottom of the eye.
11. The change of bigness in the ideas of visible objects, by distance and optic-glasses, which is the next argument he uses against visible species, is a good argument against them, as supposed by the peripatetics; but when considered, would persuade one that we sce the figures and magnitudes of things rather in the bottom of our eyes than in God: the idea we have of them and their grandeur being still proportioned to the bigness of the arca, on the bottom of our eyes, that is
affected by the rays which paint the image there; and we may be said to see the picture in the retina, as, when it is pricked, we are truly said to feel the pain in our finger.
12. In the next place where he says, that when we look on a cube "we see all its sides equal." This, I think, is a mistake; and I have in another place shown, how the idea we have from a regular solid, is not the true idea of that solid, but such an one as by custom (as the name of it does) serves to excite our judgment to form such an one.
13. What he says of seeing an object several millions of leagues, the very same instant that it is uncovered, I think may be shown to be a mistake in matter of fact. For by observations made on the satellites of Jupiter, it is discovered that light is successively propagated, and is about ten minutes coming from the sun to us.
14. By what I have said, I think it may be understood how we may conceive, that from remote objects material causes may reach our senses, and therein produce several motions that may be the causes of ideas in us; notwithstanding what P. M. has said in this second chapter against material species. I confess his arguments are good against those species as usually understood by the peripatetics: but, since my principles have been said to be conformable to the Aristotelian philosophy, I have endeavoured to remove the difficulties it is charged with, as far as my opinion is concerned in them.
15. His third chapter is to confute the "opinion of those who think our minds have a power to produce the ideas of things on which they would think, and that they are excited to produce them by the impressions which objects make on the body." One who thinks ideas are nothing but perceptions of the mind annexed to certain motions of the body by the will of God, who hath ordered such perceptions always to accompany such motions, though we know not how they are produced; does in effect conceive those ideas or perceptions to be only passions of the mind, when produced in it, whether we will or no, by external objects. But he conceives them to be a mixture of action
and passion when the mind attends to them, or revives them in the memory. Whether the soul has such a power as this, we shall perhaps have occasion to consider hereafter; and this power our author does not deny, since in this very chapter he says, "When we conceive a square by pure understanding, we can yet imagine it; i. e. perceive it in ourselves by tracing an image of it on the brain." Here then he allows the soul power to trace images on the brain, and perceive them. This, to me, is matter of new perplexity in his hypothesis; for if the soul be so united to the brain as to trace images on it, and perceive them, I do not see how this consists with what he says a little before in the first chapter, viz. " that certainly material things cannot be united to our souls after a manner necessary to its perceiving them."
16. That which is said about objects exciting ideas in us by motion; and our reviving the ideas we have once got in our memories, does not, I confess, fully explain the manner how it is done. In this I frankly avow my ignorance, and should be glad to find in him any thing that would clear it to me; but in his explications I find these difficulties which I cannot get over.
17. The mind cannot produce ideas, says he, because they are "real spiritual beings," i. e. substances; for so is the conclusion of that paragraph, where he mentions it as an absurdity to think they are "annihilated when they are not present to the mind." And the whole force of this argument would persuade one to understand him so; though I do not remember that he any where speaks it out, or in direct terms calls them substances.
18. I shall here only take notice how inconceivable it is to me, that a spiritual, i. e. an unextended substance, should represent to the mind an extended figure, v. g. a triangle of unequal sides, or two triangles of different magnitudes. Next, supposing I could conceive an unextended substance to represent a figure, or be the idea of a figure, the difficulty still remains to conceive how it is my soul sees it. Let this substantial being be ever so sure, and the picture ever so clear; yet how we
see it, is to me inconceivable. Intimate union, were it as intelligible of two unextended substances as of two bodies, would not yet reach perception, which is something beyond union. But yet a little lower he agrees, that an idea " is not a substance," but yet affirms, it is" a spiritual thing:" this "spiritual thing" therefore must either be a "spiritual substance," or a mode of a spiritual substance, or a relation; for besides these I have no conception of any thing. And if any shall tell me it is a " mode," it must be a mode of the substance of God; which, besides that it will be strange to mention any modes in the simple essence of God; whosoever shall propose any such modes, as a way to explain the nature of our ideas, proposes to me something inconceivable, as a means to conceive what I do not yet know; and so, bating a new phrase, teaches me nothing, but leaves me as much in the dark as one can be where he conceives nothing. So that supposing ideas real spiritual things ever so much, if they are neither substances nor modes, let them be what they will, I am no more instructed in their nature, than when I am told they are perceptions, such as I find them. And I appeal to my reader, whether that hypothesis be to be preferred for its easiness to be understood, which is explained by real beings, that are neither substances nor modes.
19. In the fourth chapter he proves, that we do not see objects by ideas that are created with us; because the ideas we have even of one very simple figure, v. g. a triangle, are not infinite, though there may be infinite triangles. What this proves I will not here examine but the reason he gives being built on his hypotheses, I cannot get over, and that is, that, "it is not for want of ideas, or that infinite is not present to us, but it is only for want of capacity and extension of our souls, because the extension of our spirits is very narrow and limited." To have a limited extension, is to have some extension which agrees but ill with what is before said of our souls, that they "have no extension." By what he says here and in other places, one would think he were to be understood, as if the soul, being but a small