Skiascopy and its practical application to the study of refraction / by Edward Jackson.

  • Edward Jackson
Date:
1898
Catalogue details

Licence: Public Domain Mark

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

Provider: This material has been provided by UCL Library Services. The original may be consulted at UCL (University College London)

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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 i8) 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 tlie 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 aj)parent movement is with the light on the face in hyperopia, emmetropia, and m,yopia with the point of reversal behind the observer, and against tlie 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 liyperopia, e)nmetropia, and myojjia 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 liglit on the face and against tlie mirror in hyperopia, emmetropia, and myopia of less than 1 D., and only moves with fJie ligld on tJie 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. i isnot strong eooiigl'to bnng distance of the ob5eaerse«. pia,wlieretlienioveiiient is v lens, tiie movement remains tlie plane mirror, and <\t}mi the concave minor, until a convex to over-correct the li;> the point o{ re myopia to king than the position of the observer Mtyof Movement of -Tlie rapidity with which the ■■■™^'I>^P¥l depends of the ligiit move real ^^^™<i, upon the of the real '^i^nificati movement tionof is
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