The Physiology of VisionLongman, Orme, Brown, Green, & Longsmans, 1841 - 292 pages |
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Common terms and phrases
accommodation achromatic adjustment angle of incidence angle of refraction aperture apparent magnitude aqueous humour candle choroid chromatic aberration ciliary circle colour concave contraction convex lens cornea critical angle crystalline curvature dense medium density deviation diameter different distances dispersive power distant object distinct vision diverging rays double-convex lens Dr Young effect equal experiment fibres focal centre focal distance focal length focal points foci greater inch incident ray index of refraction indistinct iris lenses less luminous measure membrane meniscus motion nearer oblique observed optic axis optic nerve optometer parallel rays pass pencil perpendicular placed plane posterior surface principal focus prism produced proportion pupil radii radius ratio rays of light reflected refracted ray refracting angle refracting surface refractive power refrangibility retina sclerotica seen sine spectrum sphere spherical aberration substance subtends supposed tance tion vertex visible direction visual angle vitreous humour
Popular passages
Page 59 - F will be a bright disc surrounded and rendered indistinct by a broad halo of light growing fainter and fainter from F to G and H. In like manner, every object seen through such a lens, and every image formed by it, will be rendered confused and indistinct by spherical aberration.
Page 208 - And first, it is certain by experience that when we look at a near object with both eyes, according as it approaches or recedes from us, we alter the disposition of our eyes, by lessening or widening the interval between the pupils. This disposition or turn of the eyes is attended with a sensation, which seems to me to be that which in this case brings the idea of greater or lesser distance into the mind.
Page 198 - new theory of visible direction " was a modification of the preceding hypothesis. This acute writer held with Aguilonius, that objects are seen single only when they are in the plane of the horopter, and consequently that they appear double when they are either 'before or beyond it ; but he attempted to make this single appearance of objects only in the plane of the horopter to depend on other principles, from which he deduced, contrary to Aguilonius, that the objects which are doubled do not appear...
Page 192 - Under the ordinary circumstances of vision the object is seen at the concourse of the optic axes, and its images consequently are projected on similar parts of the two retinae; but it is also evident that two exactly similar objects may be made to fall on similar parts of the two retinae, if they are placed one in the direction of each optic axes, at equal distances before or beyond their intersection.
Page 197 - ... be presented to the right eye and a yellow disc to the corresponding part of the left eye, instead of a green disc which would appear if these two colours had mingled before their arrival at a single eye, the mind will perceive the two colours distinctly one or the other alternately predominating either partially or wholly over the disc. In the same manner the mind perceives no trace of violet when red is presented to one eye and blue to the other, nor any vestige of orange when red and yellow...
Page 192 - ... faithful representation of any near solid object, that is, to produce a painting which shall not be distinguished in the mind from the object itself. When the painting and the object are seen with both eyes, in the case of the painting two similar pictures are projected on the...
Page 192 - When a landscape is presented to a viewer, "if those circumstances which would disturb the illusion are excluded," we could mistake the representation for reality. He declares that up to this point in history it is impossible for an artist to give a faithful representation of any near solid object. When the painting and the object are seen with both eyes, in the case of the painting two similar objects...
Page 199 - ... that cannot be explained by these laws, has, I think, been placed beyond doubt by the experiments I have brought forward. Should it be hereafter proved, that all points in the plane or in the circle above mentioned are seen single, and from the great indistinctness of lateral images it will be difficult to give this proof, the law must be qualified by the admission that points out of them do not always appear double.
Page 21 - A (Fig. 74) to which the appellation lens was originally applied from its resemblance to a lentilseed (lens in Latin) being bounded by two convex spherical surfaces whose centres are on opposite sides of the lens; the plano-convex B, having one side bounded by a plane surface, and the other by a convex surface; and the meniscus or concavo-convex C, bounded on one side by a concave, and on the other by a convex surface.
Page 78 - ... the dispersive power of the eye. He looks through a prism at a small lucid point, which of course becomes a linear spectrum. But the eye cannot so adapt itself as to make the whole spectrum appear a line; for, if the focus be adapted to collect the red rays to a point, the blue will be too much refracted, and expand into a surface; and the reverse will happen if the eye be adapted to the blue rays ; so that, in either case, the line will be seen as a triangular space.