Physiology of the special senses.

  • Major Greenwood
Date:
1910
Catalogue details

Licence: In copyright

Credit: Physiology of the special senses. Source: Wellcome Collection.

Provider: This material has been provided by Royal College of Physicians, London. The original may be consulted at Royal College of Physicians, London.

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    instrument is ±5 cm. for a distance of 20 metres, ±31-3 m. for 500 metres. Their larger instrument reads to 440 m. in 10 kilometres. If two absolutely identical pictures or impressions on a plane surface are examined Avith a stereoscope, the fused impression, as we should expect, is once more that of a flat surface. If, however, the two patterns are not absolutely much as if tlie eyes were situated at A and B. Fig. 28. identical, then, in accordance with the principles of stereo- scopic vision an imperfect appearance of relief, an obliquely vaulted image is obtained. Medals stamped with the same die but from different metals, although indistinguishable to touch or by the naked eye, have been found to produce this effect (Dove); different editions of printed books and forged bank-notes can also be detected in this way. For such purposes, a modified stereoscope, Pulfrich's Stereocom- parator, has been introduced with satisfactory results; indeed, the adaptations and modifications of Wheatstonc's instru- ment are numerous, and will in time be more so. The brief sketch presented in this chapter will, perhaps, help the reader to form an idea of the diverse fields of intellectual research which are touched on by the physio- logical study of spatial magnitude ; he will find that almost any of the branches of inquiry which each part of the subject
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