THE 



LONDON AND EDINBURGH 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[THIRD SERIES.] 



AUGUST 1832. 



XIX. On the Effect of Compression and Dilatation upon the 

 Retina. By Sir David Brewster, K.H. LL.D. F.R.S. 

 V.P.R.S. Ed* 



nPHE production of light by a gentle pressure upon the eye- 

 -■• ball, or by a sudden stroke upon the eye, is a fact which 

 has been long known, but which, so far as I know, has never 

 been carefully examined. In the sixteenth Query, at the end 

 of his Optics, Sir Isaac Newton describes the fact, and reasons 

 upon it in the following manner: 



" When a man in the dark presses either corner of his eye 

 with his finger, and turns his eye away from his finger, he 

 will see a circle of colours like those in the feather of a pea- 

 cock's tail. If the eye and the finger remain quiet these co- 

 lours vanish in a second, but if the finger be moved with a 

 quavering motion they appear again. Do not these colours 

 arise from such motions excited in the bottom of the eye by 

 the pressure and motion of the finger, as at other times are 

 excited there by light for causing vision ? And do not the 

 motions once excited continue about a second of time before 

 they cease? And when a man by a stroke upon his eye sees 

 a flash of light, are not the like motions excited in the retina 

 by the stroke? And when a coal of fire moved nimbly in the 

 circumference of a circle makes the whole circumference ap- 

 pear like a circle of fire, is it not because the motions excited 

 in the bottom of the eye by the rays of light are of a lasting 

 nature, and continue till the coal of fire in going round re- 

 turns to its former place? And, considering the lastingness of 



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

 Third Series. Vol. 1. No. 2. Ami. 1832. N 



