ODDITIES OF VISION.

Hawke's Bay Herald, Volume XXXI, Issue 10314, 28 May 1896, Page 4

ODDITIES OF VISION.

While the eyesight of many people is defective, a still greater unmber have . eyes which are unlike each other ia seeing power. In -fact, many practically make nse of one eye only; the other, . having been originally a little defective, was by degrees called on far duty less and leas, and accordingly degenerated. 003 gentleman is reported who conld see, with his right eye, the .fignres on the face of a Clock five-eighths of an inch high at 12ft, while be coald see them as clearly with the left eye only at eight inches distance, and, ourioußly enough, this extraordinary difference in the powers of vision of bath eyes was not deteotad by him nniil he had reached middle age.

Many people are unable to keep one eye shut and the other open at tho same time. This is especially common with ohildren, bub less frequent with adults, and it will be readily understood that in each cases considerable differences in the powers, of tlii eyes may exist without being suspected. Sir John Herschel mentions the casa of an elderly person wtio by chance made the unpleasant discovery that he was altogether blind In one eye. ' Some simple and easily performed experiments give interesting glimpses into Che constitution of the eye. Go into a dark room with a candle. Lookfug at the wall, which should be of a uniform dark tint, on moving the candle up and down, close to the outer aide of one eye, so that

the light falls very obliquely lntrj it,- one of what are oal'ed " Parklnja's figures" will be seen, , This 1b an appearascß of a series of diverging and branched red lines on .»' dark field, in the interspace of two or tfiree of which' ia a sort of cup-shaped disc. These lines are the blood vessels of the. reHna, and thg disc is the "yellow

Bpot" or moat sensitive pato of tha eye. -In the Btttne situation, looking still at the dark wall and keeping the eye fixed on one point, hold the candle at arm's length and move it to and fro for a d(staace of about two inches on a lavel with point towards which the eye is aiteetad, and a little to the right or left of id, when a faint light may be seen moving ' in the opposite direction to the candle and on the other side of tho point looked at. 'This light, if more nearly inspeated, ia seen to be an inverted image of the Dandle flame, equal in sfza to it, bud very fa.(nb, and is, in fact, the light of the cincJle Hfheted from the lens of the eya. Other iuterrial patta of the eye also reflect some ol the light that falls iuto it, but .the Images formed, by them are not so

easily seen. It is well known that the .pupil oonIraota mechanically in bright light and expands Jn faint light, but It baa been found that,,to some extent, bfcia change is under the control of the will. A scientific observer, writing on this' subjeot, aays that when fronting ft window or other light he can make the pspll expand or oootracd at tha desire of anyocs looking into his eye. The pupil Ia contracted while he steadily looks at the light, and when he wishes to. expand 2t all that is .necessary is to take his attention away from the eye and fix it on some other part of . the body without moving his eyes. Th{» he does, aay, by biting his tongue, plnchUiß his arm, or in some snfth' way. The seri&.'tiveness of the retina is diminished by this means, and the pupil dilates. It contracts sgalu when the mind la ones more recalled'' £o the eye and the bright Sight. Photographs have been taken of the interior of the eye, some of which show the optic nerve and the branching bloodvessels of the retinaj and others chow an inverted picture of the object's to whioh tbe eye was directed deploted on the .retina. Photographs of the eye ia darkness, taken by means of the magnssinm flash-light, show the pupil dilated to an extraordinary size, and the ids -reduced to a acre ring. '

The foot has often been noted that al times, when a sudden idea or image presents itself to tbe intelleot, there is a dig. tlnet onri sometimes even a painful sensa-

■tlon of iamlnoslty produced in the eye, •which is occasionally Intense enough to be observable even in broid daylight. A current of electricity produces a sensation it light fn the eye, and, of oonrse, everyone has Been tbe "stars" which arise . from a blow on the head. . , Helmholtz has proved that the interior - of ta» eye 1b itself laminpus, and he was able to see the movement, of his arm, in ' total' darkness, by the light of hla own eye. Sneaking of bbis ia areceoDlectnre, Professor Tesla, the fllectrlcian, called it one of the .most remarkable experiments yeoofded in. .the history of solence, and said that ptabably only a few men could satlef aottrily , repeat it, as very likely Bnoh luminosity of the eye is only found in connection with uncommon aottolty of the brain and great imaginative power. , There is a remarkabie sympathy between the eyes. So much is this the case "that any serious injury to the one is ■ almost certain to affect tbe other, hence the necessity wbica often arises for tbe removal of the injured eye mainly for the cake of saving the other. This sympathy has baen' shown by Dr. Ghauveau to exftend so-f ar that color perceived by one «ye alone axoites the retina of the other, > This is shoVD in the following way s If v white surface is observed for a short time

through' colored glass with one eye, while the other eye is screened, on removiog 1 the colored glass the white ground appears to. be tinted with ths color complementary to that of the glass. This is a common and well-known result-, bat the poind is that if the first eye is closed and the screened eye opened, tha whole surface appears tinted with the same colour as (the gluey, There are many carious optical illusions oonoeoted with color. If letters cnt ont ' of .Une and red paper fjre stack on a ecreon of bUdk velvet and^^f eared from a Bultable distance, the red lettctu appear to some people to be nearer than the bice, while abont ao many see the blue nearer than the rad. Looked at with one fyß

cosed this difference disappears, and both sets of letters appear equally distant. If one who sees the red letters nearer than

the bias covers his pupils ob the cater or temporal side with a black eoreen tine red will retreat, and soon appear to be [behind the bine ; while if one who sees the bine as nearer than the red covers his pupils on the inner or. nasal side, the leH appears to come forward and the bine to shrink back. '