Observations on the Vision of the Retina. 43 



And thi's concise expression 



Phosphate Na 2 HP 



Pyrophosphate Na 3 P 

 will convey to the French, German and Italian, as well as to 

 the English chemist, what Mr. Graham has found to be the 

 effect of a red heat in modifying the properties of phosphoric 

 acid. 



I hope Mr. Phillips may, in time, be induced to revoke his 

 unsparing sentence; and am, yours, &c. 

 Plymouth, Dec. 3, 1833. John PuiDEAUX. 



H 



XIII. Observations on the Vision 'of the Retina. By Mrs. 

 Mary Griffiths, New York.* 

 AVING for several years been attentive to the movements 

 of the eye, and of the action of light on the optic nerve, 

 I was led to investigate several very curious phenomena con- 

 nected with it. I thought with others that the retina was 

 assuredly the seat of vision, — that from that part the image of 

 all objects was conveyed to the sensory; but I have now satis- 

 factorily proved that the retina is not the seat of vision. I 

 place this proof before you, and it is the first intimation on 

 record that the subject is capable of being brought to actual 

 experiment in the living eye. 



On lying in bed one morning later than usual, quite awake, 

 but not yet having opened my eyes, the servant opened the 

 shutters very suddenly, and a bright glare of light fell directly 

 on my eyelids. To my great surprise, I saw, very distinctly, 

 the whole of the retina ! This extraordinary spectacle re- 

 mained visible to my mind for a few seconds, showing the 

 changes of light and shade which are always perceptible when 

 objects are thrown on the open eyes, having a strong light for 

 the back ground, — a phenomenon frequently noticed by all 

 writers on optics. At one moment the meshes of the net- 

 work were of a dull brick-dust colour, and the spaces between 

 were of a pale dingy yellow ; and in the next moment the case 

 was reversed, the meshes or intersections were of this pale 

 dingy yellow, and the spaces or interstices were of a dull brick 

 colour. 



My surprise was so great at first that I could do no more 

 than mark the outline and general appearance of the spectrum, 

 or retina. I had, likewise, the fear that it wasan illusion — that 

 it might be the window-sash itself which had been thus con- 



" Communicated by the Author. 

 G 2 



