490 



On Light- Sensations and the Theory of Forced Vibrations. 

 By George J. Bukch, M.A., D.Sc. Oxon, F.E.S. 



(Eeceived April 19,— Eead June 26, 1913.) 



Every hypothesis, whether mechanical, photo-chemical, or ionic, concerning 

 the connection between the light-waves and the sensations they evoke, 

 must of necessity rest ultimately on the theory of forced vibrations. It 

 seemed probable, therefore, that a model illustrating the production of 

 forced vibrations over a range comparable with that of a light-sensation 

 might be of service for teaching purposes, and might prove suggestive in 

 studying the phenomena of vision. 



The apparatus now described was made for me in May, 1909, by 

 Mr. H. Davis, the Assistant for Manual Instruction at University College, 

 Beading, and was used in my lectures both in Beading and in Oxford, but no 

 account of it has been published. From a light wooden bar, A (fig. 1), pivoted 

 at the two ends, hang a number of grey silk ribbons, varying in length 

 from 11 to 44 cm. The longest, which represent the red end of the spectrum, 

 have therefore a period twice as long as that of the shortest, which correspond 

 to violet. Each ribbon is weighted at the end with a strip of lead. 



The red sensation is represented by a scarlet ribbon occupying the 



A 



Fig.l 



Side Elevation of Oscillating Bar A, with Silk Eibbons of different lengths acting as 

 Eesonators to the Pendulum with Movable Weight B. 



