336 Dr. J. H. Gladstone on Chromatic Phenomena [Feb. 6, 



WEEKLY EVENING MEETING, 

 Friday,- February 6. 



Sir Benjamin Collins Brodie, Bart. D.C.L. F.R.S. 



Vice-President, in the Chair. 



John Hall Gladstone, Ph.D. F.R.S. M.R.I. 

 On Chromatic Phenomena exhibited by Transmitted Light. 



The origin of colour was first illustrated by some elementary 

 remarks and experiments. It was laid down as a fundamental 

 principle, that the colour of an object depends on its reflecting or 

 transmitting those rays of light which are capable of producing the 

 sensation of the said colour. The objection that a rose is red not 

 only when viewed by red light, but when seen in colourless day- 

 light, was answered by showing that a beam of colourless light from 

 the electric lamp really consisted of very many coloured rays, and 

 was resolvable by a prism into a red, orange, yellow, green, blue, 

 indigo, and violet light. This, when received on a white screen, 

 showed a brilliantly coloured spectrum, and brightly tinted objects 

 appeared of their ordinary hue only when illuminated by the ray 

 of the same colour. It was explained that the electric light closely 

 resembles that of the sun, but that the light of the great luminary 

 is deficient in certain rays, so that a prismatic spectrum formed by 

 daylight is traversed by very thin dark lines, which have been 

 mapped and designated A, B, C, D, &c. Most artificial lights 

 contain certain coloured rays in excess, hence objects illuminated 

 by them exhibit that colour more prominently than by daylight. 

 The soda flame, for instance, consists almost wholly of certain 

 yellow rays which are wanting in the sun's light, coinciding in 

 refrangibility (as Mr. Crookes has shown) with the dark line D ; 

 hence red or blue objects illuminated by it appear black, and 

 nothing is reflected from those which do appear luminous excepting 

 a ghastly yellow. 



Leaving reflected, and turning to transmitted light, it was seen 

 that pieces of coloured glass, interposed in the beam of light from 

 the electric lamp, stopped certain rays, while they allowed others 

 to pass through ; thus a red glass cut off all the blue end of the 

 spectrum, while a smalt-blue glass divided the red end into several 



