[ 80 ] 

 VIII. Proceedings of Learned Societies. 



ROYAL SOCIETY. 



[Continued from vol. xlv. p. 391.] 



March 13, 1873. — "William Spottiswoode, M.A., Treasurer and 

 Vice-President, in the Chair. 



H^HE following communication was read : — 

 •*- " Visible Direction : being an Elementary Contribution to the 

 Study of Monocular and Binocular Vision." By James Jago, M.D. 

 Oxon., A.B. Cantab., E.E.S. 



It is a well-known fact that when the eye has been displaced 

 in its socket, as, for instance, by the tip of the finger applied to 

 the eyeball through the eyelid, all objects seen by it deviate from 

 their true directions ; and the author's mode of proceeding in 

 this paper is to inquire whether visual deviations that may be 

 observed in arbitrary, but methodically devised, displacements of 

 the eyeball in its socket follow any law, and then to consider how 

 far the results thus derived are conformable with other monocular 

 and binocular experiences, and how far they may be available in 

 the explanation of certain phenomena that have been deemed ano- 

 malous in physiological optics. 



Having pointed out means by which the ball may be easily dis- 

 placed in any direction, he draws attention to the fact that, when 

 by such means the apparent directions of objects seen by the eye are 

 made to deviate from their true directions through fully 30°, the 

 orbital muscles so fully retain their command over the movements 

 of the eyeball, that that point in the visual field which was painted 

 on the point of direct sight in the centre of the foramen centrale 

 retinae still continues to be there painted. He shows this to happen 

 whatever be the direction in which the eyeball is displaced in its 

 orbit. 



This fact being a fundamental one in the inquiry he has in hand, 

 he puts it to nicer tests still. 



He adjusts the two eyes, when equally displaced so as to cause 

 objects to deviate greatly from their true directions, to look awhile 

 at the top of a high object in the open air, and having obtained a 

 strong spectrum of this object in the retinae, he, with the released 

 eyes, looks at an appropriate mark on a grey wall, and finds that 

 the spectrum really has its margin across the point of direct sight ; 

 and he tries other experiments in corroboration. 



Also by agitating a pin-hole in a card across the eye when look- 

 ing at such a high object, he brings the retina into view, and sees 

 that the point of direct sight is visibly within the foramen centrale 

 retinae, as made visible by the shadow of the wall that bounds the 

 foramen. He indicates other means of proving the same fact. 



He gathers from a series of experiments that the mastery of the 

 orbital muscles over such movements of the eyeball as are requisite 

 for pointing the optic axis to its objective point, is practically 



