A treatise on the nature of vision, formation of the eye, and the causes of imperfect vision |
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A Treatise on the Nature of Vision, Formation of the Eye, and the Causes of ... Alexander Alexander No preview available - 2019 |
A Treatise on the Nature of Vision: Formation of the Eye, and the Causes of ... Alexander Alexander No preview available - 2008 |
A Treatise on the Nature of Vision, Formation of the Eye, and the Causes of ... Alexander Alexander No preview available - 2019 |
Common terms and phrases
amber angle aperture appear aqueous humor arise assistance axis blue bright called candle cause choroid ciliare coats color concave glasses concave lens conjunctiva convex lens cornea crystalline lens dark defect degree dilated disease distant objects distinct vision DUCHESS OF KENT effect enable enter the eye Exmouth eye-brows eye-lashes eye-lids fluid focal distance foci fore frequently globe greater hole Honiton images of objects imperfect impression indistinct Infirmary intercept iris lachrymal gland lenses long-sighted Lympstone medium membrane NATURE OF VISION nearer object distinctly objects are seen oblique motion oblique muscles Oculist opacity opaque optic nerve optician orbit organ of vision particles pellucid perceived perfect portion posterior surface preserve prism pupil purposes of vision quantity of light rays of light rays passing reflected refractive power remote objects rendered retina sclerotica sensible short-sighted persons side sight spectacles Surgeon Totnes transparent violet vitreous humor
Popular passages
Page 79 - If the eyes are so fatigued by a little exercise, that we are obliged to shut them from time to time, so as to relieve them by looking at different objects. When all these circumstances concur, or any of them separately takes place, it will be necessary to seek assistance from glasses, which will ease the eyes, and in some degree check their tendency to become worse ; whereas, if they be not assisted in time, the weakness will be considerably increased, and the eyes be impaired by the efforts they...
Page i - We have been much entertained by his adventures ; several of his anecdotes are both excellent and original. The volume recalls many old favourites of the sock and buskin to our remembrance, and we cordially recommend it to all who love to hear of the strange vicissitudes of an actor's life. A Treatise on the Nature of Vision, Formation of the Eye and...
Page 4 - ... an ellipse, whose major axis is normal to the plane refracting surface ; the radiant point being in the lower focus, while the centre of the ellipse is at the intersection of the major axis with the refracting surface.
Page 60 - These were in complete plumage, and it may not be improper in this place to remark, that the...
Page 28 - The fore-part commences at the place where the cornea begins : it here attaches itself more strongly to the sclerotica by a cellular substance, forming a kind of white narrow circular rim, called the ciliary circle. The choroides separates at this place from the sclerotica, changing its direction, turning, or rather folding directly inwards towards the axis of the eye, cutting the eye, as it were, transversely.
Page 85 - ... 1. When we are obliged to remove small objects to a considerable distance from the eye, in order to see them distinctly. "2. If we find it necessary to get more light than formerly, as, for instance, to place the candle between the eye and the object. " 3. If, on looking at, and attentively considering a near object, it fatigues the eye and becomes confused, or if it appears to have a kind of dimness or mist before it.
Page 31 - ... radial fibres of the iris contract, and enlarge the pupil so as to admit a greater quantity of light. The iris is differently coloured in different persons : in some it is blue, in others brown, or of a hazel colour. The whole of the choroides is opaque, by which means no light is allowed to enter into the eye, but what passes through the pupil. To render this opacity more perfect, and the chamber of the eye still darker, the posterior surface of this membrane is covered all over with a black...
Page 79 - ... or, at least, miserable weakness of sight, is often brought on by these unsuspected causes. Those who have weak eyes should therefore be particularly attentive to such circumstances, since prevention is easy, but the cure may be difficult and sometimes impracticable. When the eye sensibly flattens, all delay is dangerous ; and the longer those, who feel the want of assistance, defer the use of spectacles, the more they will increase the failure of the eye ; there are too many who procrastinate...
Page 80 - ... seen through spectacle-glasses, no more of the glass is employed at one view than a portion equal to the size of the pupil of the eye : this on an average may be reckoned at the eighth of an inch in diameter. Thus we see how small a portion is used for the purposes of vision ; but as it would be tedious to require the eye always to look through a small aperture...
Page 4 - ... in its new direction in a straight line, and on quitting the medium, it is again abruptly bent back to its original course, provided the surface of entrance and the surface of exit be parallel to each other. Such a change in the course of a ray of light is termed Refraction.