Arcana microcosmi, or, The hid secrets of man's body discovered in an anatomical duel between Aristotle and Galen concerning the parts thereof : as also, by a discovery of the strange and marveilous diseases, symptomes & accidents of man's body : with a refutation of Doctor Brown's Vulgar errors, the Lord Bacon's natural history, and Doctor Harvy's book, De generatione, Comenius, and others : whereto is annexed a letter from Doctor Pr. to the author, and his answer thereto, touching Doctor Harvy's book De Generatione / by A.R.

CHAP. XVIII.

1. The eye bo••h watrish and fiery, imperfect vision. 2. Why the e••e is watrish, its action, spirits, and species. 3. Spirits of the e••e proved: two eyes, but one motion; why the object appears double sometimes, no colours in the eye. 4. The optick nerves soft, where united, and why. 5. The Chrystalline, and glassy humours, and white of the eye.

THough the substance of the eye be watrish, as we shewed before, yet the visive spirits are fiery, as may be seen by their light in the dark, their mobility, and their resistance to cold, for they are not molested with it as other members are▪ 2. When the imagination is vitiated, or the spirits subservient to the same are disturbed, or an opac vapour is interjected between the Cornea and chrystalline humor, wee seem to see things and colours in the air, which are not there, but this is an imperfect vision, because there is no reception of species from the air, nor is the organ distinct from the medium and object, nor is there that distance between the organ and the object, as is required in perfect vision.

II. The eye should be of a watrish substance, not fiery; because water is dense and diaphonous, fit to receive the species as it is diaphonous, and to retain them as it is dense, so is not the f••re; for though it be diaphonous, it is not dense, therefore not fit to retain the species. 2. The species being spiritual or immaterial, do not affect or hurt the eye, but the colours only hurt the eye more or lesse, as they participate more or lesse of the light, which dissipates the visive spirits, these being lucid, spend themselves on lucid objects, by reason of their cognate quality. 3. Sometimes the eye is wearied with seeing, not as vision is a reception, and so a passion, but in re∣spect of the visive spirits which are agents. 4. The eye in an instant perceives its object, though never so far distant, because the visible species are in the air contiguous to the eye, though the object be distant.

III. That there are spirits in the eye, is apparent by the di∣latation of the Ball of one eye, when the other is shut; which

is caused by the spirit passing from one eye to the other, and by reason of these spiri••s the eye is more cheerful at one time then at another. 2. Though there be two eyes, and divers m••scles, yet they are moved but with one motion, because otherwise one object would appear as two. Thus by lifting up one of our eyes with our finger, the object we look upon, appears dou∣ble, because the two Balls of the eyes are not upon the same ••uperficies, nor do the beams of both eyes equally reach the object. Thus it is with d••u••kar••s and goggle eyes, and in con••uls••ons of the muscles of the eye. ••. There are not pro∣perly any c••lou••s in the eye, becau••e then the object would seem to be of the same colour that the eye is of; yet the eyes seem to be coloured, because they are visible.

IV. The optick nerves seem of all others the most soft and spongy, that they ••ight bee the lesse offensive to the eye the most tender of all other members, and that they might convey the g••eater quantity of optick spirits. 2. They are united in∣to one, about the middle way between the brain, where they have their beginnings, and the eyes into which they are in∣se••ted, that by this union they might be the stronger, and that ••hey might be ••qually implanted into the same superficies of both eyes, lest the visive spirits bei••g unequally communicate, should occa••ion the object to appear double.

V. The Chrystallin•• humour is a part of the eye, because it hath its life, nutriment and function; as other par••s have; it is also both a similar part in its temper and substance, and it is organical in its s••tuation and figure. 2. The glass••e humour is also a part for the sa••e re••sons; therefore the Chrystalline doth not feed upon it, for no part••feeds upon another, but it prepares the blood, and alters it for the Chrystalline, left it should be infec••ed with a red colour; it affords then the same service to the Chr••stalline, which the stomach doth to the liver. 3. The white of the eye is a part thereof, and no excrement, for Nature ex••ludes excrements; but if this white should pe∣rish, sight faileth, for it is as a Bulwark to the Chrystalline, and conveyeth the species to it.