An entire body of philosophy according to the principles of the famous Renate Des Cartes in three books, (I) the institution ... (II) the history of nature ... (III) a dissertation of the want of sense and knowledge in brute animals ... / written originally in Latin by the learned Anthony Le Grand ; now carefully translated from the last corrections, alterations, and large additions of the author, never yet published ... by Richard Blome.

CHAP. V. Of Sight.

I. Why the Eyes move both toge∣ther. AS we go about to look upon any thing, both Eyes tend to the beholding of the said Object with one and the same motion, while in the mean time each of them hath its Muscles di∣stinct, and proper to its self.

The Reason hereof proceeds from the Mind, which when it sets its self intently to behold any thing, it is not to be imagined that one Eye is bent upon the beholding of that thing, and that the other is imployed upon another Object; for by that means there would be a confusion of the Rays, and of the perception in the common sen∣sorium. But both Eyes must necessarily be direct∣ed at the same time, to the same Object. And to this end the Spirits are always disposed to the ser∣vice of those Muscles which are capable of con∣verting both Eyes to this one place, and not to those which serve to draw either Eye one way, and another another; for the Mind is always bent upon seeing one thing; and tho' it often de∣signs to have the sight of many things, yet to take the better view of each, it takes it in a certain order, and views them one after another; which may quickly be done, if the things to be seen are near enough and big enough to be easily and soon beheld.

II. How a Flea and a Horse may both seem to be of the same magnitude. Who ever looks upon a Flea near at hand, and extends his sight to a Horse or other Animal of like magnitude at a very great distance, they will appear equal, and offer themselves to view under the same magnitude.

This is evident from Opticks, by which it is thus made out, namely that the faculty of seeing, or rather the Soul residing in the Brain, appre∣hends Objects to be greater or lesser, according

as they were represented to the sight under a greater or lesser angle. So that when as a Flea being seen very near at hand, and a Horse at a remote distance, seem both under the same angle, they are look'd upon by the Soul as equal: For it is evident that an Object is there∣fore apprehended greater, because it impresses a greater affection upon the Retin Tunicle or Optick Nerve, and lesser so far as the lesser proportion of the Organ is affected. Hence it is that the farther a thing recedes from us, so much the lesser it appears; and by how much the nearer it ap∣proaches us, so much the bigger it shews, in re∣gard the Object, by how much the farther it is re∣moved from us, appears with so much the acuter and smaller angle, and impresses the lesser affecti∣on. The Reason of all this is, because while the Object recedes and withdraws it self by little and little from the Eyes, it is not only diminished as to its circumference, but as to all the parts which are turned towards the Eye, because tho' it always remits its Rays in like manner from each point, yet most of them according to the rate of their recess and elongation, slip beside the Eye, and are elsewhere disposed.

III. Convex things ap∣pear afar off as if thy were plain. In like manner those things which are seen afar off, tho' they are square and angular, yet they seem round in regard the distance of the angles cuts off the excursions and asperities; so we receive Convexes as they were plain, because all inequality of parts, by reason of so great an interval to∣tally disappears. Hence the Sun and all the Stars appear to our sight not convex but plain; for tho' their middle parts are nearer to our Eyes than the extreme, yet that difference is but very small, if compared with so great a distance.

IV. Why an ap∣pearance in a Looking Glass seems to be beyond the Person looking. An Image of any one beheld in a Looking Glass, appears as much beyond it, as the Specta∣tor Stands on this side it.

The Reason is, because the Spectator beholds his Face in the Glass, not as fix'd therein, but as sliding from him; and consequently the matter is to be considered, as if the Spectator were from the Looking Glass behind himself; whence it comes to pass, that the same distance is repeatedly apprehended by a reciprocal comparison: And be∣cause this reflexion causeth no necessity of the Spectators being transferred into the place of the Looking Glass, or altering his situation to be con∣verted again into himself, it comes to pass, that af∣ter the Axis which is directed from the Spectator to the Glass, he immediately receives an Axis which tends from the Glass to the Spectator; and because of the unalterableness of the situation, hath both for the same continued Right Line, whose middle is from the Spectator to the Glass, the other half from the Glass to the Image beyond the Glass, where the Spectator represents from whence he comes.

V. How it is that an Ob∣ject may distinctly be discerned through a small hole. An Object which appears too confused, as being too near the sight, may distinctly enough be seen, if any one behold it through a little hole made with a Pin or Needle in a Card or piece of Wri∣ting Paper.

The Reason is, because the Eye then receiving a lesser quantity of Rays from every point of the Object, every one of them describes its Image alone in a very narrow space; and so they which proceed from the two Neighbouring Points, scarce make any confusion in their Act∣ings.

VI. Those that dive into the water, see Objects only confu∣sedly. Urinators or Divers see Objects confusedly in the bottom of the Waters, except they make use of very Convex Glasses.

The Reason is, because the Rays of Light are not sensibly broken when they pass from the water into the aqueous or watry humour of the Eye; and so those that proceed from the same point are not again compelled by falling into the Retin Tu∣nicle, which may be gained by the use of very Convex Glasses.

VII. How low Objects come to seem high, and high, low. Things presented to the sight, by how much the farther they are distant, so much the higher they appear, and on the contrary high things so much the lower.

The Reason is, because things near at hand emit those Rays which smite the superiour parts of the Eye, or Retin Tunicle; whereas things re∣mote send forth those Rays which arrive at the inferiour region of the Eye; and when the Objects in the Retin Tunicle are form'd with an inverted situation, those must needs seem more deprest and low, these more sublime. On the contrary it hap∣pens, when we convert the sight of the Eye to things plac'd on high; for then those things which are at a greater distance seem lower, in so much that the utmost bound of Heaven appears as it were conterminous to the Horizon: Forasmuch as that part of the Heaven which is our Vertical point, affects the lowest part of the Eye, and the other parts emit Rays, so much the more sublime by how much the more remote they are; hence that appears the supream of all, and the rest are so much the more sublime, by how much the nearer they approach to the Vertex; and so much the more deprest and low, by how much the farther they receed from it.

VIII. Objects ceasing to be seen when the Pupil is contracted. Objects sometimes by the contraction of the Pu∣pil or Apple of the Eye are hidden to the sight, as if any one should direct his sight to some remark∣able Star, for example, Venus or Jove, and by some Art should contract the Pupil of the Eye, the Star at first seen will by degrees disappear, and at length totally fly the sight.

The Reason of this is drawn from part of the said Pupil, which according to the rate of the said coarctation or dilatation, causes the Object to be seen, or to fly the sight: For since upon the contraction of the Pupil it receives fewer Rays under a smaller angle, it causes the Object to appear less, and con∣sequently if they are so few as to be comprehend∣ed in an insensible angle, they will no way affect the Retin Tunicle, so far as is required to Vision; and as that affection is not perceived, so neither will the Object which ought to be perceived by the mediation thereof, be any farther deprehended. For it conduces to the rendring of that affection insensible, that in the contraction of the Pupil, the Chrystallin Humour be somewhat relaxt; whence it comes to pass, that the bottom of the Retin Tunicle goes back so little, and becomes more weak by the incidence of the Elapsed Rays; which two things are sufficient to make the Object, at the contraction of the Pupil, to disappear, and what was seen before, to become afterwards invi∣sible.

IX. How the Stars come to appear bigger by Night, and lesser by Day. Hence it is that the Stars appear lesser by Day than by Night, when our Hemisphere is overlaid with darkness, namely by reason of the Pupil in the light, and the expansion of it when it is dark. For it is certain, that the Pupil, when ever light takes place, is rendred more narrow, and conse∣quently that fewer Rays from a flame of Fire en∣ter the Eyes, and that a lesser portion of the Retin Tunicle is affected; but the Air being overspread with darkness, it plainly appears that the Pupil is dilated, and consequently that many more Rays arrive at the Eye, and that a greater portion of the Retin Tunicle being affected, a greater species also of the Object is produc'd therein. Hence also it comes to pass, that the magnitude of the Stars seems in the Evening to increase, and so in the Morning to decrease; by reason that the Pupil in the Evening Season is by little and little dilated, and in the Morning by little and little contracted, and by this means the Retin Tunicle is ever less and less affected. So the flame of a Candle, if by Day it be beheld a hundred paces off, it appears very small, but upon the coming on of the Evening, it began to grow bigger, till Night at length increased it to the appearance of a con∣siderable Torch.

X. How some Men dis∣cern Objects at a very great di∣distance. It is reported of STRABO, that he was of so sharp and quick an Eyesight, that he could discern Fleets setting Sail from out of Lilybaeum, a Port of the Carthaginians, at the distance of above a hundred miles: Moreover, LOPEZ, a Spaniard at Gades, is related to have been able to discern from the top of the Mountain Calpe on the Europaean side, to the opposite Shore of Africa, over the whole Bay between, which by the Testimony of Cleonardus in his Epistle to Jacob Laboc, is in a Calm Sea no less than three or four hours sail, and that so distinctly, that he could relate many things he saw there done.

This so wonderful a sharpness of sight de∣pends mainly upon a double disposition of the Per∣sons so indued, first from the docility of the Chry∣stallin Humour, and the easie use of the Ciliary Processes; namely, whilst according to the diffe∣rent incidence of Rays reflected from the Objects, the Chrystallin Humour is in such a manner adapt∣ed and disposed as an exact projection requires. 2dly, It is necessary that the Capillaments of the Retin Tunicle be so exquisitly disposed, as to re∣ceive the least affection. Because altho' those things which we behold with our Eyes cannot be discerned, but so far as in some sort they differ in colour, yet a distinct perception of Colours pro∣ceeds not only in this, that all the Rays proceed∣ing from all points of Bodies meet in the bottom of the Eye, in so many other Rays, or thereabout; but also from the multitude of the Capillaments of the Optick Nerve, whose extremities are con∣tain'd in that space which the Image in the bottom of the Eye possesses. Whence no doubt is to be made but STRABO and that Spanish LOPEZ injoyed so accurate a contexture of the Retin Tunicle, and had so docile a Chrystallin Humour, that they were able to contemplate Objects more distinctly than others, and have a prospect of them at so vast a di∣stance.

XI. How it is that some Men see by Night. From this very cause it happens, that some Men, like Owls, see even in the darkest Night, as it is related of the Emperour NERO and others, namely, that they have most slender and very moveable Fibres, of which their Optick Nerves are framed; so that that little Light which remains in the most obscure Nights, suffices to affect their Fibres, and to excite the sense of see∣ing in them.

XII. How a Bo∣dy appears where it is not. If a Stick fired at the end be swiftly whirl'd about, there will appear to our sight the Image of a fiery Circle, tho' the Stick be not in all points of the Circle.

The Reason hereof is, because the Stick makes an impression in those parts of the Retin Tunicle which are circularly disposed; so as that the fore∣parts being agitated by the celerity of the moti∣on, still retain something of its impression, whilst it agitates the last parts. For this motion is not at one and the s••me individual time, but in di∣vers successions of Moments, so swiftly performed, that the Vibration of Fire imprest upon the Eye, remains in the first parts of the Retin Tunicle▪ when the Stick hath declined to the other parts of the Circle. When no wonder if the Rays en∣tring the Eye by the Pupil, oft-times effect at once a sensation of Greenness, Redness, Blackness, Whiteness, and other Colours; because the Rays modified by divers Colours, in divers successions of Motions following each other with incredible swift∣ness, hit upon the Retin Tunicle, and leave a lit∣tle while their agitation, till other Rays present∣ly entring the Pupil, impart in their turn their motion, and there leave it some time with o∣others.

XIII. How it is that they who have a Cataract concht, see obscurely. Those that have a Cataract Couch'd, discern but obscurely all visible Objects; whereupon that they may the more clearly and distinctly see them, they make use of Convex Glasses.

To make this the more clear and evident, we must observe, that a Cataract is not any Skin (as hath been long believed) growing between the Chrystallin Humour and the Uveous Tunicle, which may be taken off by a Needle, and drawn down to the inferiour part of the Eye, but that it is the Chrystallin Humour it self, which in tract of time grows flaccid and weak, and is separated from the Ciliary processes, as an Acorn when ripe, is easily separated from its Cup, forasmuch as it is removed with little or no trouble, and deprest to the very bottom of the Vitreous or Glassy Humour, a small part, in the mean time, of the said Vitre∣ous Humour succeeding in its place. The Cata∣ract therefore being thus taken away, the Chry∣stallin Humour also must of necessity be taken away, or at least be rendred more plain, or less convex, whereby it comes to pass that the Rays proceeding from all points of the Object, are not sufficiently broken or made bending, so as to be united in the Retin, when they arrive there: Whence the Vision or act of Sight must needs be confused. To which infirmity the Chrystallin Convexity only gives relief, as causing the Rays which before were divergent to become conver∣gent, and to enter the Eye with such a disposi∣tion.

XIV. Divers Co∣lours ap∣pear upon sight of the Sun. Upon sight of the Sun, or any other Glaring Light, we seem to behold various Colours.

The Reason is, because such is the nature of our Mind, as by virtue of the motions that occur in that part of the Brain whence the tender Filaments of the Optick Nerves proceed, to be capable of having a Sense of Colour; whereupon in regard the Agitation by which, after the Eyes shut, the Capillaments of the Optick Nerve still palpitate, and as it were tremble, is not strong enough to render the Light so bright, as that was from whence it came, it represents Colours less intense, and as it were dilute; but that these Colours are produc'd from motion, may from hence be easily concluded, namely that grow∣ing pale by little and little, they are changed, and passing mutually into each other, vanish by degrees.

XV. How it comes that the top of a Mountain far distant seems conti∣guous to the Hori∣zon. The top of a Mountain reaching far beyond the visible Horizon, appears to us as joined with it, together with the Hill it self, and the Sun when it rises or sets seems to adhere to, and be united with the said Horizon.

The Reason of this appearance is, because things appear at no distance from us, when the Rays cohere, and without the interposition of other Bodies apply to our Eyes; as it happens in the forementioned case: Forasmuch as tho' there is a vast distance between the Sun and the Hori∣zon, and many Bodies are contain'd therein, yet because none of those Rays arrive at us, but only from the Sun and the Horizon, it happens that they seem among themselves contiguous and co∣hering. For the distance of the Horizon is no other ways known by us, than from the diversity of Bodies interpos'd between us and them; whence if those intermediate spaces should happen to be obstructed, and nothing of them could possibly be transmitted to us, we must needs judge those things which we see afar off, to be contiguous and separated by no interval. Wherefore GAS∣SENDUS thinks that Dogs bark at the Moon, because they apprehend it to rise near the House top, and so to be very little more distant than the House it self, and not much bigger than that part of the House comprehended by it.

XVI. Ditches from a low place ap∣pear joined together. So if we behold many Ditches, the sides of them plainly appear to us as not much distant from each other, because they are represented to us by Rays from the Eye, to which many also that slide from the bottom, mingling themselves, are carried upward; but if we behold those Ditches Horizontally, or from a low place, their sides seem to us to have no distance at all, because no Rays proceeding from the bottom, reach the Eye, and those which proceed from the sides, stick as they arrive.

XVII. Why Drun∣ken Men see double. Drunken Men see every Object double, which VIRGIL asserts also of Mad Men. 4 Ae∣neid.

This proceeds from the dark and malignant Va∣pours, either flowing from the Wine, or stirred up by the malignity of the Distemper, which while they pervert the situation of the Optick Nerves, they make such a percussion of the Brain at the same time, as if the Rays exhaling from the Ob∣jects, proceeded from detorted Eyes: Whence those that by Nature, or any chance or accident, have their Eyes drawn awry, see all things double.

XVIII. Why we see from the dark, things set in the light We find by daily experience, that standing in the dark, we plainly see things put in a lightsom place, but not on the contrary, from a light place things set in the dark.

The Reason is, because the Rays of Light may be directed to the Eye, being in a misty or dark place, that some of them may make their way into the said obscure place, if the passage be open enough, and the Light gliding through it into the Pupil of the Beholder, arrive as far as the Retin Tunicle. But he who is in the midst of the Light, cannot apprehend those things which are in an ob∣scure place, because from thence no Rays proceed, which either directly or by reflection can touch the Retin Tunicle; unless by chance the darkness be some way or other intermingled, and remit some Rays of Light; for then nothing would hinder, but that a few Rays reflext from things would sensibly affect the Eye, and represent some sort of Image of things.

XIX The Hyper∣boreans have gene∣rally very weak Eyes. The Hyperboreans or Inhabitants of the most Northern Countries, have generally bad Eyes, and are dim-sighted.

The Reason is, because they are perpetually conversant in Snow, which above all things re∣flects back the Light, by reason whereof their Eyes must needs be strain'd, or because their Retin Tu∣nicle, hardned by the external brightness, is less capable of expressing, or entertaining an affection necessary for Sight. When as we see that the Chrystallin Humour becomes congealed with cold, and attains to such a rigidity or stifness, that it can neither be bent, nor contracted, nor un∣folded.

XX. Bodies mo∣ved with a rapid swiftness are not perceived. A Cannon Bullet, or any dark Body, passing with incredible swiftness through a whited Wall, becomes altogether imperceptible.

The Reason is, because the dark Body, as like∣wise that so rapidly moved, making no impression upon the Eyes, so lightly, at that time, interrupts the reflection of the Rays of Light from the Wall, that the Eye, for that small interval of time, pre∣serves the commotion which those Rays immedi∣ately before produc'd. The contrary whereof we find by experience in a Firebrand whirl'd round, in regard the Brand impresses its force up∣on the parts of the Retin Tunicle formed into a round, because then the rapidity of the motion causes the part first moved to keep yet a little while that impression which the Brand makes upon the last.

XXI. Why Gog∣gle-eyed Persons cannot see clearly at any great distance. Those that have prominent or Goggle Eyes, as the Myopes or Purblind People, see not Objects di∣stinctly at any great distance.

The Reason is, because the Rays of Light dri∣ven and refracted upon the prominent Eyes, meet sooner than they can arrive at the bottom of the Eye; Forasmuch as they represent the Image, not in the Retin Tunicle, but on this side; namely in the Vitreous Humour. Wherefore Goggle-eyed Persons are wont to make use of Prospective Glas∣ses, because by them the Rays are divided, and do not so soon concur and meet together.

XXII. The Object is varied according as it is re∣presented in divers Glasses. An Object in a plain Glass appears just as big as it is, but in a Convex, less; and in a Concave, greater.

The Reason is, because a plain Glass remits to∣wards the Eye all the Rays from each direct point of the Object, and thereby every thing must needs

be represented just as big as it is. Whereas the Convex, by reason of the obliquity of the inci∣dence, diversly disperses this way and that way a great part of the Rays; whence it is that few of them are directed into the Sensorium; and on the contrary, the Concave not only remits to the Eye the Rays which are reflected from the plain, but also very many more, which come from the little devexitated regions of particles, and those of points also elsewhere obverted. Whence it comes to pass, that the Figure is increas'd, and exceeds in mag∣nitude the represented Object.

XXIII. Why some Men see nothing, but at some cer∣tain di∣stance. Some Men perceive not Objects, except at some certain distance, in so much that either ve∣ry near, or very far off, they see but confu∣sedly.

The Cause hereof is chiefly custom, as when Men use themselves to look at such a distance; for the Muscles which are disposed to the immutati∣on of Figure, are rendred as it were stupid, and unapt for their wonted functions; not otherwise than the rest of the Muscles of the Body become unuseful for the motion of the Members, after they have stood long unmoved. To which may be added, that the Membrans which contain the three Humours of the Eye, may possibly have be∣come so hard, as not to be so flexible as for∣merly.

XXIV. How a Blindman saw a lit∣tle, by com∣pressing his Eye. A certain Young Man being blind, while he prest either Eye towards his Nose with his Finger, could see a little, otherwise nothing at all.

Possibly this might be, because by the said compressing of the Eye, he inverted the convexity of the Chrystallin or Uveous Humour; whence followed a change of the Projection, and conse∣quently another Affection. In like manner as when holding to our Eyes a Leaf of a Book printed in a very small Character, we keep one Eye shut, and press the other down with two Fingers, we shall fancy the Letters to be increased, and be∣come bigger.

XXV. Why the whole Sun cannot be seen in an Optick Tube. The whole Discus of the Sun cannot be seen by the help of an Optick Tube, tho' the whole Image be projected upon an opposite sheet of Paper.

The Cause hereof is, by reason that the Optick Tube, in respect of its Cavity, divides the many Rays, and suffers them not to fall into the Eye; whereas all the Rays of the Sun fall upon the Paper, and form therein a far more large Effigies of the Sun.

XXVI. Vision is made much more di∣stinct, by a hole made by a Needle in a Card or Paper. An Object which appears confused, as being too near the Eye, may be seen distinctly enough at the same distance, by any one through a hole made with a Needle in a thin Card or piece of Writing Paper.

The Reason is, because the Eye, then receiving a lesser quantity of Rays from every point of the Object, each of them forms its Image, even in a very narrow space; so that those which proceed from the two Neighbouring points scarcely con∣found their actions.

XXVII. How a Stone at the bottom of a Vessel comes to be seen by the pouring in of Water. If any one putting a Stone or Counter into a Vessel, so place it, that he can no longer discern it, yet by pouring water into the Vessel, directing his Eye precisely to the same place, he will see the Counter or Pebble sticking at the bottom of the Vessel, tho' it did not appear there be∣fore.

To this there can be assigned no other Cause, than that the Rays reflected before from the Coun∣ter, there being then no sort of Body interposed between, were directly sent into the Air, and by consequence smote nothing but the Forefront, and neighbouring parts of the Eye: But upon the in∣fusion of the Water, the Beams passing through it, are refracted, and so applying towards the Eye, render the Stone visible and conspicuous thereun∣to. Thus we see in the refraction of the Rays made in the Horizon, the Sun being 34 minutes high or thereabouts, appears much higher to us, than it would appear, if those Vapours were absent, through which the Rays of Light are transmitted, and consequently being half a degree and 30 mi∣nutes diameter, it may be all seen, tho' deprest and wholly underneath the Diameter.

XXVIII. How things viewed through a Convex Chrystal Glass ap∣pear. Things appear bigger than they really are, through a Convex Chrystal Round: As we find by experience in old Men, who being not able to discern Letters, tho' near at hand, help their sight in reading, by using the Convex Glasses of a pair of Spectacles: As also in those that make use of Microscope Glasses, for the viewing and discerning of the Hairs of a Flea, and even the minutest and smallest Bodies imaginable.

The Reason is, because in a Convex Glass plac'd between the visible Objects and the Eye, the Rays which before came short, and hardly reach'd the Ball of the Eye, are forc'd into the Pupil, so that the Eye receives the Rays from the particles of the Objects formerly hid; and since the Rays before join'd with them are separated from those inter∣posed, and many particles seen from each part, they must needs be thereby inlarged, and represent the whole bigger. For when the angle is inereast, the visible Object coming next in view, by reason of the great divarication of the Rays entring cross∣ways the Pupil of the Eye toward the Retin Tu∣nicle, must needs form a great Image in the bot∣tom of the Eye.

XXIX. Through a Telescope things ap∣pear grea∣ter. Hence it comes to pass, that through a Telescope or Optick Tube, we see things at a good distance, in their full magnitude, and discern them very di∣stinctly. For this advantage a Telescope brings, that it causes the visible Object, by reason of the great Pupil of the Tube to be discerned with more Rays, and by reason of the convexity of the ut∣most Glass gathering the Rays under a greater an∣gle of Vision. Moreover the divarication becomes great, of those Rays, which entring cross-ways the Pupil or utmost extremity of the Tube, to∣wards the Retin Tunicle of the Eye, cause a large Image of the visible Object to be described in the bottom of the Eye.

XXX. Why from two Eyes any Object appears singular. The Object appears singular, or but one, tho' transmitted to the Brain through both Eyes; and tho' the Optick Nerves meet not in conjunction, as appeared in the dissection of a certain Young Man, in which VESALIUS found them to be separate or divided.

The Reason of the simplicity of Objects is re∣ferred to the Conarion or Pineal Glandule, situate in the midst of the Brain, in which the two Ima∣ges, which proceed from the two Eyes, are united before they arrive at the Soul. For there is no other part in the Brain which is not double. For as for the Cerebellum, except in superficies and name, it is not one: Nay, it is manifest that its

Vermiformous or Worm-formed Process, and the Marrow of the Spina Dorsi consists of four parts; two whereof proceed from the two Medieties of the Brain; the other two from the two Medieties of the Cerebel: But the transparent Septum, or Fence which separates the two formost Ventricles is also double, and consequently that Pineal Glan∣dule only is single, in which the Species proceed∣ing from both Eyes may meet, before they are conveyed to the Soul.

XXXI. Why the Picture of a Man seems to look upon all Persons in the Room. A Painted Person seems to cast an Eye upon every part round about him, and as it were to look upon every one in the Room particularly.

The Reason hereof is, that the Eye of the Pi∣cture is in plain, and consequently the Rays may be brought from all its points to the Eye of the Beholder. But the Eye of the Living Person be∣ing of a Convex Figure, and a great part of it hid, it is not able to send out its Rays every way, as we find apparent in Carved Images, whose Eyes being exerted or sticking out, and shapt into a certain Curvity or Convexity, cannot emit the Rays every way.