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III. A paper was in part read, entitled " Ocular Spectres and 

 Structures as Mutual Exponents." By JAMES JAGO, A.B. 

 Cantab., M.B. Oxon., Physician to the Royal Cornwall 

 Infirmary. Communicated by "W. J. KENWOOD, Esq. 

 Received December 26, 1854. 



The paper opens by stating that for want of a methodical elimi- 

 nation of ocular spectres from one another a want which its aim is 

 to meet physiological optics remain to this day without any real 

 foundation ; and even when we have followed the rays of light 

 through all the refracting media of the eye, we cannot safely assert 

 what sensations belong to them until we have detected everything 

 connected with the percipient membrane which may obstruct the 

 action of light on it, or which may originate sensations as of light 

 through other sorts of impulses. Our eyes in many important re- 

 spects provide us with an opportunity for microscopical research 

 that no optical instrument employed on the dead eye can rival. We 

 may thus gather a variety of information, physical and physiological, 

 solve points of ocular structure that escape other means of investi- 

 gation, and bring a profusion of ingenious speculations to a termina- 

 tion, by showing that the phenomena (and this is especially true of 

 the retinal phenomena) which have occasioned them are simply 

 exponential of anatomical facts ; and important physiological laws 

 may be arrived at by like means. 



The first step in the author's task is to determine the conditions 

 which render objects existing upon or within the eye visible by their 

 shadows, and to obtain optical principles by which we may examine 

 the interior of our own eye with facility, so as to recognize in what 

 lenticular structure, and what part of it, the cause of any shadow or 

 " diffractive image " resides. He shows that we may make every 

 measurement of interest, may decide all the points just alluded to, at 

 the instant, as it were, by mere inspection ; and he illustrates his 

 optical principles by appropriate experiments. 



The paper then commences its actual elimination of ocular spectres 

 from one another, starting from the appendages of the eye and going 

 on through the ocular tissues in succession to the retina, under 

 several heads, as 



