The clinical use of prisms : and the decentering of lenses / by Ernest E. Maddox.

  • Ernest Edmund Maddox
Date:
1907
Catalogue details

Licence: In copyright

Credit: The clinical use of prisms : and the decentering of lenses / by Ernest E. Maddox. 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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    prism is correctly marked, the vertical line appears unbroken, as in Fig. 22, but if not, the part of the line seen through the prism appears disjointed from the rest and displaced, as in Fig. 23, towards the side of the real apex. It only remains to rotate the prism till the unbroken appearance of Fig. 22 is gained ; then the point on the prism's edge in apparent coincidence with ' I Fig. 22.—]\Iode described for Fig. 23.—Appearance with a testing the apex of a prism. badly marked prism. the point of intersection of the lines may be regarded with confidence as the real apex. Greater distance of the prism from the vertical line magnifies the phenomenon, and makes the test more delicate. The true base of a prism can be found and marked in just the same way as the apex. To those who manufacture prisms in large quantities it may be permissible to suggest a special apparatus which I have designed to mark the apex with mathematical accuracy. Each prism should be laid on a horizontal glass plate, with one longitudinal line at some little distance beneath it. Two pins or projections