Skiascopy and its practical application to the study of refraction / by Edward Jackson, A.M.,M. D.

  • Jackson, Edward, 1856-1942.
Date:
1896
Catalogue details

Licence: Public Domain Mark

Credit: Skiascopy and its practical application to the study of refraction / by Edward Jackson, A.M.,M. D. Source: Wellcome Collection.

Provider: This material has been provided by University of Bristol Library. The original may be consulted at University of Bristol Library.

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    he watches in the pupil with the known direction of the real movement on the retina, to determine whether he sees an erect or an inverted image. When the apparent and real movements are in the same direction, he knows (page 18) he is looking at the eye from a distance shorter than that for which it is focused. When the apparent and real movements are in the opposite directions, he knows that he is looking at the eye from a distance greater than that for which it is focused. ' The direction of the apparent movement of the light then, will be with the light on the face in hyperopia and in emmetropia at all distances, and in myopia when the eye is viewed from a point nearer than its point of reversal. The apparent movement in the pupil will be the opposite of the real movement only in cases of myopia when the eye is viewed from somewhere beyond its point of reversal. With the plane mirror, the apparent movement is with the light on the face in hyperopia, emmetropia, and myopia iirith the point of reversal behind the observer, and against the light on the face in myopia viewed from beyond the point of reversal. With the CONCAVE mirror the apparent movement is against the light on the face in hyperopia, emmetropia, and myopia with the point of reversal behind the observer; and is with the light on the face only in myopia viewed from beyond the point of reversal. This statement made to conform to the practice customary in the use of the concave mirror [where the observer keeps a constant distance of i metre from the eye, corresponding to i D. of myopia], would be: the light moves against the light on the face and against the mirror in hyperopia, emmetropia, and myopia of less than 1 D., and only moves with the light on the face in myopia of more than 1 D. When we speak of inverted movement with the concave mirror, this movement with the mirror and with the light on the face is meant.