Report of the Committee on Colour- Vision. 309 



and the night test is with the absolute colours of signals. We 

 give some puzzling colours at night, one of which is an orange 

 light. The tints are graduated, we only use 4 glasses, white, red, 

 gTeen, and orange. All the glasses are of the same intensity. We 

 do not try to imitate fogs, we simply have the lamp at the back 

 of the glass, and the man in front; the room being darkened. I 

 find larger lights are more easy to distinguish than smaller ones 

 The light behind the coloured glass is 10 or 12 candle power. It 

 is not used with a bull's eye ; it is a perfectly plain glass. Our 

 signals are with bull's-eyes, with plain glass in front for colours. 

 The plain glass is certainly a more severe test than with a bull's- 

 eye, for I myself can see the flame through the colours. 



Question. — If you look at the blue glasses in a lamp outside a 

 chemist's shop, you often see the flame is red. Might not a 

 mistake be made somewhat in this way ? — I think it might confuse 

 men not accustomed to artificial lights. I think our test a very 

 severe one, and a large number of men fail to pass. I could hardly 

 say what percentage. The diameter of the lights used on the lines 

 is about 6 inches. The man can see these lights a mile away. At 

 300 yards with. a 6-inch light across he could see to stop a train 

 well. I am speaking approximately, of course. The test at 

 3 yards with the disc as large as a sixpence is about equal to the 

 6-inch light at the distance of 24 yards. The man is wanted to see 

 the latter at 300 yards, but we have the smaller light, which is 

 perhaps only ^th of an inch. [Mr. Rix, who is colour-blind, was 

 here called and tested by the witness, who stated that he had 

 passed to his satisfaction.] Witness explained that with the traffic 

 men the question is not of such importance as with drivers and 

 firemen, who are in charge of the train and mind the brakes ; the 

 sight of the traffic men is not tested so severely as the drivers 

 and firemen. [Witness exhibited the specimens of the glasses 

 actually in use in the signals and in the lamps ; also samples of 

 the coloured signal flags.] 



Mr. Priestley Smith's evidence was to the following effect:— 



^Acquired Colour Blindness differs in one important respect from 

 congenital Colour Blindness — the congenital defect is often asso- 

 ciated with a normal form-sense, while the acquired defect is 

 always, or almost always, associated with more or less loss of the 

 form-sense ; that is to say, a man who has once had a normal 

 colour-sense cannot lose it without losing more or less of his 

 form-sense. (Leber has collected several supposed exceptions to 

 this rule, but they are not conclusive, and are doubted even by 

 Leber himself. ' Graefe-Saemisch Hand-Book,' vol. v, p. 1037.) 



" In testing the visual function it is important to distinguish 

 between the central and the more peripheral parts of the field. 

 The centre of the retina — the macula lutea — is the part used in 

 looking accurately at any object. The object is seen with much 



