The Physiology of VisionLongman, Orme, Brown, Green, & Longmans, 1841 - 292 pages |
Contents
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Common terms and phrases
achromatic adjustment angle of incidence angle of refraction aperture apparent magnitude appear aqueous humour axis candle choroid chromatic aberration ciliary circle colour convex lens convex surface cornea crown glass crystalline curvature dense medium density deviation diameter different distances dioptric instruments dispersive power distant object distinct vision distinctly diverging rays double-convex lens effect equal experiment fibres focal centre focal distance focal length focal points foci greater horopter images formed inch incident ray index of refraction indistinct inverted image iris lenses less luminous magnitude membrane meniscus microscope nearer oblique observed optic axes optic nerve parallel rays pass pencil perpendicular placed principal focus prism prismatic produced pupil radii radius rays of light rays proceeding reflected refracted rays refracting angle refracting surface refractive power refrangibility retina sclerotica screen seen sine spectrum sphere spherical aberration substance subtends supposed tance telescope tion vertex violet rays vitreous humour
Popular passages
Page 274 - 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 258 - 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 257 - ... 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 252 - ... 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 252 - 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 262 - ... 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 40 - 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 126 - ... 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.
Page 256 - C' remains fixed, the screw having previously been removed. Though the single appearance of two images of different size is by this experiment demonstrated, the observer is unable to perceive what difference exists between the apparent magnitude of the binocular image and that of the two monocular images ; to determine this point the stereoscope must be dispensed with, and the experiment so arranged that all three shall be simultaneously seen ; which may be done in the following manner : — The...
Page 264 - ... very little of the violet. The yellow space, which has not been much absorbed, has increased in breadth. It occupies part of the space formerly covered by the orange on one side, and part of the space formerly covered by the green on the other. Hence it follows that the blue glass has absorbed the...