375 



the development (as it is technically called) of latent photographic 

 images, must, for the reason mentioned, be abandoned. It will still, 

 of course, be competent to compare normal and abnormal vision with 

 photographic effects, as phenomena displaying analogy, though not 

 affinity. 



To one other relation of the retina to light, I make the briefest 

 reference. If only those rays which are reflected from the choroid 

 produce, by their impact on the retina, the objective perception of 

 light, and if the depth of tint of the yellow spot be considerable, and 

 its colour at all homogeneous, then perfect vision must be exercised 

 by yellow, not white light. But if this be the case, we should be 

 unconscious of red and blue when seeing best, or at least should re- 

 ceive from them an impression very different from that which they 

 occasion when they affect the general surface of the retina. I for- 

 bear, however, to speculate on this, seeking rather to direct the 

 attention of the few anatomists who have the opportunity of inves- 

 tigating the subject to an examination of the chromatic as well as 

 the actirtic relations of the yellow spot, than desiring to dogmatize 

 on either.* 



P.S. — I take this opportunity of expressing my regret, that in a 

 postscript, added after it was read, to the paper in the Transactions 

 of the Society for last session, " On the Eye as a Camera Ohscura^'' 

 I inadvertently misstated the views of Professor Goodsir on the re- 

 tina referred to in this communication, and had not an opportunity 

 of amending the statement before the Transactions were published. 

 I have, therefore, to request those who wish to do justice to Mr 

 Goodsir, to consult his lecture on the Retina, published in the 

 *^ Edinburgh Medical Journal^^ for October 1855. 



The following Donations to the Library vy^ere announced : — 



The Assurance Magazine, and Journal of the Institute of Actuaries, 



Vol. vi., Part 3. 8vo. — From the Institute. 

 Proceedings of the Ashmolean Society, 1855. 8vo. — From the 



Society, 



* According to some eminent authorities, there is an aperture in the centre 

 of the yellow spot. If such be the case, light may pass and repass by it with- 

 out being coloured j but as such light will in both journeys fail to impress the 

 retina, it cannot contribute to the production of a luminous sensation. 



2i 2 



