File:Outlines of comparative physiology touching the structure and development of the races of animals, living and extinct - for the use of schools and colleges (1870) (14595968550).jpg

Identifier: outlinesofcompar00agas (find matches)
Title: Outlines of comparative physiology touching the structure and development of the races of animals, living and extinct : for the use of schools and colleges
Year: 1870 (1870s)
Authors: Agassiz, Louis, 1807-1873 Gould, Augustus A. (Augustus Addison), 1805-1866 Wright, Thomas, 1809-1884
Subjects: Physiology, Comparative Zoology
Publisher: London : Bell & Daldy
Contributing Library: MBLWHOI Library
Digitizing Sponsor: MBLWHOI Library

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stance fromthe eye, say at a ; for therays of the pencil whichproceeds from the object atc, come precisely to a focusupon the retina, at c. Ifthe pin be now placed atb, the rays will centre atg, in front of the retina, andthe object be then seendouble at d and f. Thesame thing happens whenthe pin is removed to agreater distance than a,say to e; the pencil of raysin this case could only cen-tre after their refraction bythe lens at h, far beyondthe retina, so that the sin-gle object is necessarilyagain seen double at i andk. Double vision of thiskind sometimes occursalong with partial opaci-ties, streaks and specks ofthe cornea. (§ 135. Although thereare two images formed bythe refracting media uponthe retina of the two eyes,still in ordinary vision wesee objects single, not double. This depends on the condi-tion or quality of particular spots of the two retinae. Ob-jects, to wit, are seen single when the axes of the two eyesmeet in the object contemplated. In this case the point fixed
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OF SIGHT. 67 by the eyes, I, in the accompanying diagram (fig. 43), falls uponthe two terminal points of the two eyes axes, a and I. Thepoints in the two eyes, A and B, which correspond or aresimilarly situated, with reference to all surrounding points m

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