Binoculars

“ Frequently, however, even a slight impediment to binocular fusion, such as the application of a red glass to one eye, suffices to procure preponderance in the elastic tensions of the muscles, and to cause the fixed point to appear double. We can put a stop to binocular single vision still more surely by applying to one eye a prism with the base upwards or downwards. ”

“ In all, or nearly all, perfect eyes the lens is flatter in front than behind, and this enables us to see things far off by bringing the rays from them exactly to a focus on the retina. But when we look at nearer things the rays require to be more bent or refracted, so without any conscious effort on our part this ciliary muscle contracts and allows the lens to bulge out slightly in front. Instantly we have a stronger magnifier, and the rays are brought to the right focus on the retina, so that a clear and full-size image of the near object is formed. ”

“ Binocular alternation of vision.—It was while experimenting on the phenomena of recurrent vision that I discovered the curious fact that in normal eyes the two do not see equally well at a given instant, but that the visual effect in each eye undergoes fluctuation from moment to moment, in such a way that the sensation in the one is complementary to that in the other, the sum of the two sensations remaining approximately constant. Thus they take up the work of seeing, and then, relatively speaking, resting, alternately. This division of labour, in binocular vision, is of obvious advantage. ”

“ As the eyes of different persons are not the same distance apart, the first and most important point to observe in using the binocular is that each eye has a full and clear view of the object. This is easily tried by closing each eye alternately without moving the head, when it may be found that some adjustment is necessary by racking out the draw-tubes D, E, of the bodies by means of the small milled head near the eye-pieces ”

“ For, as we have been told, “to look at anything means to place the eye in such a position that the image of the object falls on the small region of perfectly clear vision, ... and ... whatever we want to see, we look at, and see it accurately; what we do not look at, we do not, as a rule, care for at the moment, and so do not notice how imperfectly we see it.” Such is the case, as has been shown, for when we fix our sight on the principal object or motif of a picture, binocular vision represents clearly by direct vision only the parts of the picture delineated on the points of sight. ”

“ The apparatus of rods, cones, and other structures are absolutely essential to enable light to give that stimulus to the optic nerve which, conveyed to the brain, is converted into visual sensations. So if this apparatus were absent in our organs of vision, in vain would the optic nerve proper be spread out over the interior of the eyeball: we should be no more able to see with such eyes than we are able to see with our hands.
We now invite the reader’s careful consideration to the diagram, Fig. 236, which is a section of the retina through the yellow spot. ”

“ By appropriate muscular training the eyes may be directed, each slightly outward, so that these lines meet behind the observer's head while the object, apparently duplicated, is seen still in front. The recognition of the subjective fusion of the two eyes into a Cyclopean, or central binocular eye, is a fundamental prerequisite for the explanation of vision in the stereoscope. ”

“ If expense is not an object, a binocular instrument should be purchased, and it is well to be provided with an object-glass as low as three or even four inches focus, which will allow the whole of objects having the diameter of half an inch or more to be seen at once. ”

“ ALL of the forms under which the stereoscope has come into general use have been devised with a view to creating to the utmost the illusion of natural binocular perspective by reproducing as nearly as possible the conditions of natural vision. That this end is not successfully attained is painfully felt by those who linger too long over an attractive collection of stereographs. To secure comfortable vision the muscles of the eyes must suffer no unusual strain. ”

“ Similarly, then, on their emergence they are refracted chiefly by the lens and cornea, so as to form an image in the outer air, the emergent rays coinciding in their path with that which they took when entering, and the image formed in the air being conjugated with the retinal image; being formed, therefore, on the same side, varying with the position of the lens and object, and the accommodation of the eye. ”

“ The pictures were not taken in a binocular camera, and therefore do not stand out well, but, by moving one or both until the eyes coincide in the stereoscope, the pictures blend perfectly. If taken in a binocular camera for the purpose, each person being taken on one-half of the negative, I am sure the results would be still more striking. ”

“ The habit of suppression may become so dominant that binocular fixation continues to exist for distant objects and the presence of binocular fusion is easily traceable, while for near objects, which are monocularly fixed with relative divergence, it is impossible to render the patient conscious of the images of the deviating eye. ”

“ In concluding this chapter, it may be proper to remark, that unless we require an increased relief for some special purpose, landscapes and buildings should be taken with the normal binocular camera, that is, with its lenses 21⁄2 inches distant. Scenery of every kind, whether of the picturesque, or of the sublime, cannot be made more beautiful or grand than it is when seen by the traveller himself. ”

“ In this way an objective existence may appear to be given to the binocular eye by approaching a mirror until the nose touches the glass, and avoiding the convergence of visual lines that would otherwise be natural. A narrow face is seen, possessing but a single eye, that looks into the very depths of the observer's Cyclopean eye. ”

“ With others, all efforts are in vain, it is impossible to render them conscious of the double images, notwithstanding that the presence of the binocular disturbance of vision proves that the habit of binocular fixation exists. ”

“ Such eyes are best developed in Asaphus, Illænus, Nileus, Bumastus, Proëtus, etc."
2. Eyes with biconvex lenses.
The surface of the eye is a mass of contiguous lenses, covered by a thin membrane which is frequently absent from the specimens, due to poor preservation. The lenses are biconvex, and being in contact with one another, are usually hexagonal, although in some cases they nearly retain their globular shape. Such eyes are found in Bury care, Peltura, Sphæropthalmus, Ctenopyge, Goldius, Cheirurus, and probably others. ”

“ A good binocular, preferably one which magnifies about six times, is a great aid to the amateur. The field of the glass, its illumination, ease of adjustment, and such points should be investigated before the purchase is made. A well-made glass with good lenses is probably the best in the long run, even though it be more expensive. ”

“ Is it not curious, that so vast a being as the whale should see the world through so small an eye, and hear the thunder through an ear which is smaller than a hare’s? But if his eyes were broad as the lens of Herschel’s great telescope; and his ears capacious as the porches of cathedrals; would that make him any longer of sight, or sharper of hearing? Not at all.—Why then do you try to “enlarge” your mind? Subtilize it. ”

“ It is impossible that the eye should project from itself, by visual rays, the visual virtue, since, as soon as it opens, that front portion [of the eye] which would give rise to this emanation would have to go forth to the object and this it could not do without time. And this being so, it could not travel so high as the sun in a month's time when the eye wanted to see it. ”

“ The eye—which sees all objects reversed—retains the images for some time. This conclusion is proved by the results; because, the eye having gazed at light retains some impression of it. After looking (at it) there remain in the eye images of intense brightness, that make any less brilliant spot seem dark until the eye has lost the last trace of the impression of the stronger light. ”

“ The eyes of some persons are large, others small, and others of a moderate size—the last-mentioned are the best. And some eyes are projecting, some deep-set, and some moderate, and those which are deep-set have the most acute vision in all animals; the middle position is a sign of the best disposition. ”

“ Sudden and magnificent, the sun’s broad golden disc showed itself over the horizon facing them; and the first rays, shooting across the level water-meadows, took the animals full in the eyes and dazzled them. When they were able to look once more, the Vision had vanished, and the air was full of the carol of birds that hailed the dawn. ”

“ I ask how far away the eye can discern a non-luminous body, as, for instance, a mountain. It will be very plainly visible if the sun is behind it; and could be seen at a greater or less distance according to the sun's place in the sky. ”

“ That light is not itself a substance may be proved from the phenomenon of interference. A beam of light from a single source is divided by certain optical methods into two parts, and these, after travelling by different paths, are made to reunite and fall upon a screen. If either half of the beam is stopped, the other falls on the screen and illuminates it, but if both are allowed to pass, the screen in certain places becomes dark, and thus shows that the two portions of light have destroyed each other.
Now, we cannot suppose that two bodies when put together can annihilate each other; ”

“ There could be no want of finish where Nature has worked, and here, where all harmonises to the eye, she has prepared, for the grand burst of harmony for the ear, that wondrous concert that surely begins on one particular undated morning in spring, when, as if moved by a single impulse, all bird-dom breaks forth into song—a song of praise so sweet and glorious that the heart seems to leap, ay, and does leap, back over the gulf of years, to feel as in childhood’s days, before rust, canker, and the world’s own wear had hardened it to what it is. ”

“ THE BODY WHICH IS NEAREST TO THE LIGHT CASTS THE LARGEST SHADOW, AND WHY? If an object placed in front of a single light is very close to it you will see that it casts a very large shadow on the opposite wall, and the farther you remove the object from the light the smaller will the image of the shadow become. ”

“ No small hole can so modify the convergence of rays of light as to prevent, at a long distance, the transmission of the true form of the luminous body causing them. ”

“ At this time the crops are approaching maturity; the vast fields of maize have been passing through the various stages of green, waving, flag-like leaf, and hidden immature cob, with its beautiful, delicate tassel, prelude of the golden amber or black treasure that is to come and gladden the eye of the spectator in every direction. ”

“ I think it was his eye! yes, it was this! One of his eyes resembled that of a vulture—a pale blue eye, with a film over it. Whenever it fell upon me, my blood ran cold; and so by degrees—very gradually—I made up my mind to take the life of the old man, and thus rid myself of the eye for ever. ”

“ And when the elderly man refused to listen and mumbled on, an odd image came to his mind of a lighthouse besieged by the flying bodies of lost birds, who were dashed senseless, by the gale, against the glass. He had a strange sensation that he was both lighthouse and bird; he was steadfast and brilliant; and at the same time he was whirled, with all other things, senseless against the glass. ”

“ All still as death, and no eye upon its actions but the stars of heaven, as it were, spirits looking down to chronicle what passed. The rattling of a shutter bar—the grating noise as of iron upon iron, mingled with the crackling of woodwork; the figure wrenching and tearing with maniacal fury at the firm fastenings, while huge drops of sweat roll down his face. More resistance; more noise; but the figure, straining with the might of a giant, again and again, till the iron snaps in the frosty air; and then, wrenched out by its protecting bar, an iron-sheeted shutter lies upon the pavement. ”

“ Why, it is like a park!”
For gazing to the left, or northward, his eye ranged over the lovely undulating Sussex Weald, with its park-like, well-wooded hills and valleys, now in the first blush of their summer beauty, the leafage all tender green, and the soft meadowlike pastures gilded with the dazzling yellow of the over-abundant crowfoot. ”

“ all the rays which convey the images of objects through the air are straight lines. Hence, if the images of very large bodies have to pass through very small holes, and beyond these holes recover their large size, the lines must necessarily intersect. ”

“ Quite a crowd had gathered on the broad, glistening patch of rugged granite, as soon as the day broke, and this crowd was ever augmenting, till quite a phalanx of oilskin coats and tarpaulin hats presented its face to the thundering sea, while men shouted to each other, and swept the lead-coloured horizon with heavy glasses, or the naked hand-shaded eye, in search of some vessel trying to make the harbour, or in distress. ”