THE 



LONDON AND EDINBURGH 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[TyiRD SERIES.] 



SEPTEMBER 1832. 



I 



XXXVII. On the Undulations excited iti the Retina hy the 

 Action ofEuminous Points and Lines. By Sir David 

 Beewster, K.H. LL.D. F.R.S. V.P.R.S. Ed* 

 N the theory of vision, the light which radiates from visible 

 objects is supposed to act only on those parts of the retina 

 upon which it directly falls. To this principle, however, there 

 are some exceptions. If a white circle is placed upon a green 

 ground of some extent, the colour of the circle will not ap- 

 pear white but red, or the accidental colour of green. In like 

 manner, if a narrow slip of white paper placed upon a green 

 ground is viewed indirectly by the eye, it will vanish entirely 

 as if it had been removed, and the space which it occupied 

 will appear green. In both these cases the green light has 

 acted upon a part of the retina upon which it did not fall, 

 producing in the first case its accidental colour, and in the 

 second case its own eolour. When the retina is under the 

 influence of a very strong light, the colour^ of every object 

 which is painted upon it is either changed,'or diminished in 

 intensity, although the image is not formed upon any part of 

 the retina which is directly affected by the strong light. 



When light in the form of luminous lines in bright points 

 acts upon the retina, a series of remarkable phsenomena are 

 produced, which, in so far as I know, have not hitherto been 

 noticed. In giving an account of the experiments which I have 

 made on this subject, I shall begin with the simplest case of 

 a line of light. 



• Read at the meeting of the British Association at Oxford, June 22, 1832. 

 Third Scries. Vol. 1. No. 3. Sept. 1832. Z 



