THE 

 LONDON, EDINBURGH and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[THIRD SERIES.] 



JUNE 184.2. 



LXVI. Some Observations on the Action of Light on Revolving 

 Discs. By A. Milward, Esq.*- 



1. rpHE object of this paper is to explain some interesting 

 A effects produced by the action of light, and especially 

 electric light on discs in rapid revolution, figures or represen- 

 tations of various kinds being depicted on their surfaces. 



2. The general action of light in producing upon the retina 

 the image of any object when in a state of rest, consists in a 

 number of successive waves impinging upon all parts of the 

 object, and being reflected thence to the eye. Each wave 

 reflected from each portion of the surface, produces by itself 

 a minute effect : and a series of such successive waves would 

 evidently increase such effect, in a degree dependent upon the 

 constitution of the eye. It is found by experiment that the 

 retina is capable of retaining an image impressed upon it ; or 

 in other words, that the nerves of the retina continue their 

 vibration for a definite period of time, which we will repre- 

 sent by w" ; if .•. a" be the interval between the waves, and n" 

 the time of duration of the first wave of a system, the duration 

 of the effect of the successive waves before the extinction of 

 the first, will be {n"-a") (k"-2«")&c {v>< -){n-\)a\ 



and at the completion of w" the — waves will have produced 



on the retina the greatest effect which it is capable of receiving, 

 since the further addition of waves will be compensated for by 



the corresponding loss of all those anterior, to the — wave 



from the last. Hence the time required for the formation of 



• Communicated by the Author. 

 Phil. MoQ. S. S. Vol. 20. No. 133. Jime 1842. 2 H 



