THE 



LONDON and EDINBURGH 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[THIRD SERIES.] 



APRIL 1834. 



XL I. On the Influence of successive Impulses of Light upon 

 the Retina. By Sir David Brewster, LL.D., F.K.S. } 

 V.P.R.S. Ed. 

 TjMlOM the remarkable experiment of Mrs. Griffiths, de- 

 -*- scribed in a former Number*, it appears that the reti- 

 culated structure of the retina may be rendered visible by 

 throwing light suddenly on the closed eye when in a state of 

 repose, and especially in the morning, before the retina has 

 been subjected to the action of any other light. 



In repeating this experiment, I have found that a remark- 

 able structure may be exhibited at any time, and whether the 

 eyes are open or shut, by subjecting the retina to the action 

 Of successive impulses of light. If, when we are walking be- 

 side a high iron railing, we direct the closed eye to the sun 

 so that his light shall be successively interrupted by the iron 

 rails, a structure resembling a kaleidoscopic pattern, having 

 the foramen ccntrale in its centre, will be rudely seen. The 

 pattern is not formed in distinct lines, but by patches of red- 

 dish light of different degrees of intensity. When the sun's rays 

 are powerful, and when their successive action has been kept 

 up lor a short time, the whole field of vision is filled with a 

 brilliant pattern, as if it consisted of the brightest tartan, com- 

 posed of red and green squares of dazzling brightness. The 

 green colours prevail chiefly at the centre, corresponding to the 

 foramen ccntrale, and here we observe tlie dark-lined network 

 Mttern which I have described in Number 20f, anil which 

 is totally distinct from the reticulated structure noticed by 



• Sec Lond. and Edinb. Phil. Mag., vol. iv. p. 4:?. \ Ibid. p. 1 1!), note. 



Third Seriei. Vol. I. No. 22.' April 1834. 2 I 



