Ways To Perfect Vision

How do we perfect our vision?

This can be done through 3 principal parts:

1. The objects

Some objects are close or accessible. Others are distant and inaccessible.

Some are illuminated, others less.

We can approach or move away from accessible objects and increase or decrease the light that illuminates them.

But we cannot do this for remote objects.

2. The internal organs which receive the actions of these objects

We cannot add anything by art to the structure of the nerves and the brain because we cannot make a new body.

3. The external ones which dispose these actions to be received as they should.

The external organs for sight include:

• all the transparent parts of the eye
• all the other bodies that can be placed between it and the object.

All the things of note with these external organs can be reduced to 4 points.

1. All the rays which go to each of the ends of the optic nerve do not come from only 1 part of the object.

They do not undergo any change in the space between the two.

Without this, the images they form could not be either very similar to their original or very distinct.

2. These images are very large in the extent of their lines or their features

They will be all the easier to discern the larger they are.

3. The rays that form them are strong enough to move the small fibers of the optic nerve

This makes them felt, but not so strong as to injure the sight.

4. There are as many objects as possible whose images are formed in the eye at the same time

As many as possible can be seen at a single glance.

Nature has filled the eye with very transparent liquors which are not tinged with any color, it has caused the actions which come from without to pass to the bottom without changing;

By the refractions caused by the surfaces of these liquors it caused that between the rays, according to which these actions are conducted, those which come from the same point gather together in the same point against the nerve, and then that those which come from the other points also gather there in as many other various points as exactly as possible: for we must suppose that nature has done in this all that is possible, especially since experience does not makes us see nothing in it, on the contrary.

In order to lessen the defect which cannot in this case be entirely avoided, she has made it possible to shrink the pupil almost as much as the strength of the light permits; then, by the black color with which she dyed all the parts of the eye opposite the nerve, which are not transparent, she prevented any other ray from going towards these same points;

By changing the shape of the body of the eye, it has caused that, although the objects may be more or less distant from it once the other, the rays which come from each of their points do not never fail to always assemble, as exactly as possible, at as many other points at the back of the eye. However, it has not so completely provided for this last part that there is not yet something to add to it: for, besides the fact that, commonly to all, it has not given us the means of curving so much the surfaces of our eyes that we can distinctly see objects that are very close to them, as if at a finger or half a finger distance, it has failed even more in some to whom it has made eyes of such a shape that they can only serve them to look at distant things, which happens mainly to old people; and also in a few others to whom, on the contrary, she has made them such that they only serve them to look at close things, which is more usual for young people; so that it seems that the eyes form at first a little longer and narrower than they ought to be, and that afterwards, as one grows older, they become flatter and wider.

In order that we may remedy these defects by art, it will first be necessary for us to seek the shapes which the surfaces of a piece of glass or of some other transparent body must have in order to bend the rays which fall on it in such a way that all those which come from a certain point of the object arrange themselves, by crossing them, just as if they had come from another point which was nearer or more distant, namely, which was nearer to serve those who are short-sighted, and which was further away both for old people and generally for all those who want to see objects closer than the shape of their eyes allows. For, for example, the eye B or C[28], being disposed to cause all the rays which come from the point H or I to assemble in the middle of its background;

and, not being able to, to also cause those of point V or X to assemble there; it is obvious that, if we put in front of it the glass O or P, which causes all the rays from the point V or X to enter inside just the same as if they came from the point H or I, we will compensate by this average to its defect. Then, because there may be glasses of several different shapes which have in this exactly the same effect, it will be necessary, in order to choose the most suitable for our purpose, that we again take heed principally to two conditions, of which the first is, that these figures be the simplest and easiest to describe and to carve that it will be possible; and the second, that by their means the rays which come from other points of the object, like EE, enter the eye almost as if they came from as many other points, like FF: and note that I only say here approximately, not as much as possible; for, apart from the fact that it would perhaps be rather difficult to determine by geometry, among an infinity of figures which can serve for this same purpose, those which are exactly the most suitable for it, it would be entirely useless, because the eye even if they do not cause all the rays which come from various points to assemble precisely at as many other various points, they would doubtless not therefore be the most suitable for making the vision quite distinct; and it is impossible in this to choose otherwise than approximately, because the precise shape of the eye cannot be known to us. Moreover, we will always have to take care, when we thus apply some body before our eyes, that we imitate, as far as possible, nature in all the things that we see that she has observed in them. building, and that we lose none of the advantages it has given us, except to gain some more important one.

For the size of the images, it should be noted that it depends only on three things, namely the distance which is between the object and the place where the rays which it sends from various of its points towards the bottom intersect. of the eye, then of that which is between this same place and the fundus of the eye, and finally of the refraction of these rays.

As it is obvious that the image RST[29] would be larger than it is, if the object VXY were closer to the place K where the rays VKR and YKT intersect, or rather to the area BCD which is properly the place where they begin to cross, as you will see below: or, if we could make the body of the eye longer, so that there would be more distance than there is. there is from its surface BCD, which causes these rays to intersect, to the bottom RST; or, finally, if the refraction did not bend them so much inwards towards the middle S, but rather, if it were possible, outwards. And whatever one imagines besides these three things, there is nothing that can make that picture bigger. Even the last is hardly at all considerable, because one can never increase the image by its means more than very little, and this with so much difficulty that one can always do it more easily by one. others, so you will know everything now. So we see that nature has neglected it; for, causing the rays, like VKR and YKT, to curve inwards towards S on the surfaces BCD and 123, it made the RST image a little smaller than if it had made them curve outwards, as they are about 5 on the area 456, or she would have let them be straight. There is also no need to consider the first of these three things when these objects are not at all accessible; but, when they are, it is evident that the more closely we look at them, the larger their images are formed in the depths of our eyes, so much so that nature has not given us the means of looking at them more closely than about a foot or half a foot away; in order to add to it by art all that is possible, it is only necessary to interpose a glass such as that which is marked P[30] of which it has been spoken

everything now, which causes all the rays which come from a point as near as possible to enter the eye as if they came from another point more distant: now all the more that one can do by this means, there will be only the twelve or fifteenth part of as much space between the eye and the object as there ought to be without it, and as well as the rays which will come from various points of this object, crossing twelve or fifteen times nearer to it, or even somewhat closer, because it will no longer be on the surface of the eye that they will begin to cross, but rather on that of the glass to which the object will be a little closer, they will form an image whose diameter will be either twelve or fifteen times greater than it could be if one did not use this glass: and consequently its surface will be about two hundred times larger, which will cause the object to appear about two hundred times more distinctly, by means of which it will appear as much p greater, not exactly two hundred times, but more or less in proportion to what is judged to be remote. Because, for example, if, looking at the object X through the glass P, we position our eye C in the same way as it should be to see another object which would be twenty or thirty paces from it, and that, having no knowledge of the place where this object X is, we judge it to be really thirty paces away, it will seem more than a million times larger than it is, so that it can become from a flea an elephant; for it is certain that the image which a flea forms at the back of the eye, when it is so close to it, is no less great than that which an elephant forms there when it is thirty paces away. And it is on this alone that the whole invention of these little smart glasses is based, composed of a single lens, the use of which is quite common everywhere, although the true figure has not yet been known. they must have: and, because we usually know that the object is very close when we use them to look at it, it cannot appear so large as it would if we imagined it further away.

There remains only one other means of increasing the size of the images, which is to cause the rays which come from various points of the object to cross as far as possible from the fundus of the eye; but it is without comparison the most important and the most considerable of all, because it is the only one that can serve for inaccessible objects as well as for accessible ones and whose effect has no limits: so that one can, by using it, increase the images more and more up to an indefinite size: as, for example, as much as the first of the three liquors with which the eye is filled causes almost the same refraction than common water, if we apply everything against a pipe full of water, like EF[31], at the end of which there is a GHI glass, whose shape is very similar to that of the BCD skin which covers this liquor , and even relates to the distance from the bottom of the eye, there will no longer be any refraction at the entrance to this eye; but that which was done there before, and which was the cause that all the rays which came from the same point of the object began to bend from that place to go and assemble at the same point on the extremities of the object. optic nerve, and that then all those which came from various points cross there to go to return on various points of this nerve, will be done as of the entry of the tube GI; so that these rays, crossing from there, will form the image RST much larger than if they crossed only on the surface BCD, and they will form it larger and larger, according as this pipe is longer. And thus the water EF doing the office of the humor K, the glass GHI that of the skin BCD, and the entrance of the pipe GI that of the pupil, the vision will take place in the same way as if nature had made the eye longer than it is the whole length of this pipe, without there being anything else to notice, except that the real pupil will then be not only useless, but even harmful, in that it will exclude by its smallness the rays which could go towards the sides of the fundus of the eye, and thus prevent the images from extending there in as much space as they would if it were not so narrow. I must also not forget to warn you that the particular refractions, which take place a little differently in GHI glass than in EF water, are not considerable here, because this glass being everywhere equally thick. , if the first of its surfaces makes the rays bend a little more than would that of water, the second straightens them as much at the same time; and it is for this same reason that above I have not spoken of the refractions which the skins which envelop the humors of the eye can cause, but only of those of its humors.

Now, all the more so since it would be very inconvenient to join water against our eye in the way that I have just explained, and even since, not being able to know precisely what is the shape of the BCD skin which covers it, we cannot determine exactly that of the GHI glass to substitute it in its place; it will be better to make use of another invention, and to make, by means of one or more glasses, or other transparent bodies also enclosed in a tube, but not joined to the eye so exactly as to only a little air remains in between, that, as soon as this pipe enters, the rays which come from the same point of the object bend or bend in the way that is required, to make that they go to gather in another point towards the place where the middle of the bottom of the eye will be when this pipe is put in front. Then, once again, let these same rays, on leaving this pipe, bend and straighten up in such a way that they can enter the eye just as if they had not been bent at all, but only that they came from some nearer place; and then that those who will come from various points, having crossed at the entrance of this pipe, do not uncross at the exit, but that they go towards the eye in the same way as if they came from a object that was larger or closer.

As if the pipe HF[32] is filled with an entirely solid glass whose surface GHI is of such figure that it causes all the rays which come from the point X, being in the glass, to tend towards S; and that its other surface KM folds them again in such a way that they tend from there towards the eye in the same way as if they came from the point x, which I suppose in such a place that the lines xC and CS have between themselves proportion than XH and HS; those coming from point V will necessarily cross them in the area GHI, so that, being already far from them, when they are at the other end of the pipe, the area KM will not be able to bring them closer, mainly if it is concave, as I suppose, but it will send them back towards the eye in much the same way as if they came from the point v, by means of which they will form the RST image all the larger as the hose will be longer; and it will not be necessary, in order to determine the figures of the transparent bodies which one will want to use for this purpose, to know exactly what is that of the surface BCD.

But, for what it would once again be inconvenient to find glasses or other such bodies which were thick enough to fill the entire HF pipe, and clear and transparent enough not to prevent the passage of light , we can leave empty the whole inside of this pipe and put only two glasses at its two ends, which have the same effect as I have just said that the two surfaces GHI and KLM should have. And it is on this alone that the whole invention of these glasses is based, composed of two lenses placed at the two ends of a pipe, which gave me the opportunity to write this treatise.

For the third condition which is required for the perfection of sight on the part of the external organs, namely that the actions which move each thread of the optic nerve be neither too strong nor too weak, nature has provided for it very well in us. giving the power to shrink and widen the pupils of our eyes; but it still left to art something to add to it: for, firstly, when these actions are so strong that one cannot shrink one’s pupils enough to suffer them, as when one wants to look at the sun, it is easy to remedy it by placing against the eye some black body, in which there is only a very narrow hole which does the office of the pupil; or by looking through a crape or some other such somewhat obscure body, and which only lets into the eye as many rays from each part of the object as are needed to move the optic nerve without injuring it. And when, on the contrary, his actions are too weak to be felt, we can make them stronger, at least when the objects are accessible, by exposing them to the rays of the sun so picked up with the help of a mirror or glass. burning that they have the most strength they can have to illuminate them without corrupting them.

Then, besides that, when one uses the glasses of which we have just spoken, especially since they make the pupils useless, and it is the opening through which they receive the light from outside that does its job, it is also this that we must enlarge or shrink, depending on whether we want to make the vision stronger or weaker. And it should be noted that, if we did not make this opening wider than the pupil is, the rays would act less strongly against each part of the fundus of the eye than if we did not use spectacles: and this in same proportion as the images which would be formed there would be larger, without counting what the surfaces of the interposed glasses deprive of their force. But it can be made much wider, and this all the more so as the glass which straightens the rays is situated nearer to the point towards which the one who bent them made them tend. As if the GHI glass causes all the rays that come from the point we want to look at to tend towards S[33], and that they are straightened by the KLM glass, so that from there they tend parallel towards the eye: to find the greatest width that the opening of the pipe can have, it is necessary to make the distance which is between the points K and M equal to the diameter of the pupil; then, drawing from the point S two straight lines which pass through K and M, namely SK, which must be extended as far as g, and SM as far as i, we will have gi for the diameter which we are looking for: for it is manifest that, if it were made larger, there would not therefore enter into the eye more rays from the point towards which one raises one’s sight, and that, for those who would come there from other places, not being able to help to the vision, they would only make it more confused.

Diopter figure 31.jpg

But if, instead of the KLM glass, we use klm, which, because of its shape, must be placed closer to the point S, we will once again take the distance between the points k and m equal to the diameter of the pupil; then, drawing the straight lines SkG and SmI, we will have GI for the diameter of the opening sought, which, as you see, is greater than gi in the same proportion as the line SL surpasses Sl.

And if this line Sl is not greater than the diameter of the eye, the vision will be nearly as strong and as clear as if one did not use glasses, and if the objects were as a reward closer than they are not, especially as they appear larger: so that, if the length of the pipe causes, for example, the image of an object thirty leagues away to form as large in the eye as if it were only thirty paces distant, the width of its entrance, being such as I have just determined it, will cause this object to be seen as clearly as if, being really only thirty paces distant from it, one looked at him without glasses. And if we can make this distance between the points S and l even less, the vision will be even clearer.

But this is mainly only useful for inaccessible objects; because, for those who are accessible, the opening of the pipe can be all the more narrow as one approaches them more, without for that that the vision of it is less clear; as you can see that no less rays from the point X[34] enter the small glass gi than the large GI; and finally it cannot be wider than the glasses that are applied to it, which, because of their shapes, must not exceed a certain size, which I will determine below.

That if sometimes the light which comes from objects is too strong, it will be very easy to weaken it by covering all around the extremities of the glass which is at the entrance to the pipe, which will be better than putting a few others in front glasses more cloudy or colored, as many are wont to do to look at the sun: because, the more this entrance will be narrow, the more the vision will be distinct, as it was said above of the pupil. And it must even be observed that it will be better to cover the glass from the outside than from the inside, so that the reflections which may be made on the edges of its surface do not send any rays towards the eye; for these rays, not serving the vision, could harm it.

There is now only one condition which is desired on the part of the external organs, which is to make one perceive as many objects as possible at the same time; and it is to be observed that it is in no way required for perfection to see better, but only for the convenience of seeing more, and even that it is impossible to see more than one object at a time distinctly: in so that this convenience, of seeing several others confusedly, is mainly useful only in order to know towards which side one will have to turn one’s eyes afterwards to look at the one among them that one wishes to better consider: and c This is what nature has provided so much that it is impossible for art to add anything to it; even quite the contrary, especially since, by means of a few glasses, one increases the size of the lineaments of the image which is imprinted at the bottom of the eye; especially as it represents fewer objects, because the space it occupies cannot be increased in any way, except perhaps very little by turning it upside down, which I judge be rejected for other reasons. But it is easy, if the objects are accessible, to put the one you want to look at where it can be seen most distinctly through the telescope; and, if they are inaccessible, to put the telescope on a machine which is used to turn it easily towards any determined place that one wishes. And so we shall lack nothing of what makes this fourth condition most significant.

For the rest, so that I do not omit anything here, I still have to warn you that the defects of the eye, which consist in the fact that one cannot sufficiently change the figure of the crystalline humor or the size of the sloe, can be gradually diminished and corrected by use, because this crystalline humor and the skin which contains this sloe being real muscles, their functions are facilitated and increased when they are exercised, thus than those of all the other muscles in our body. And it is thus that hunters and sailors, by practicing looking at very distant objects, and engravers or other craftsmen who make very subtle works, by looking at very close ones, usually acquire the power to see them. more distinctly than other men. And it is thus also that these Indians, who are said to have been able to gaze fixedly at the sun without their sight being obscured by it, must no doubt have previously, by often gazing at very bright objects, gradually accustomed their pupils to shrink more than ours. But these things belong rather to medicine, the end of which is to remedy the defects of sight by the correction of the natural organs, than not to dioptrics, the end of which is only to remedy the same defects by the application some other artificial organs.