44 COLOUR-SIGHT AND COLOUR-BLINDNESS 



— as the standard for the determination of colour vision. " The 

 great point in a test is to cause the candidate to do somethiny to 

 show that he appreciates colour. It is this domy something and 

 saying nothing which is the important feature of the Holmgren 

 test. A man may be ignorant of the names of colours — colour 

 ignorant, it is called — but he cannot be ignorant of the colours 

 themselves if he has normal colour vision." 



So when a candidate is handed a single skein and asked to 

 match it or pick out from the many skeins before him all he 

 thinks like it he is subjected to a very practical test. He may 

 — he very often does — say when handed the test skein " Oh, 

 that is a green." The answer is, " Then pick out all the 

 greens you see." But he is not requested or even encouraged to 

 name colours. 



Quite recently, 1902, at a meeting of ophthalmologists in 

 England an attempt was made to throw discredit upon the wool 

 test and a resolution was proposed that " the employment of the 

 Holmgren test for colour-blindness by the Board of Trade is 

 most unsatisfactory, as the inefficiency of this test is now well- 

 known." Twenty-four members were present but only seven 

 voted and the motion was lost by one vote. 



There are other wool arrangements, Jeafifreson's frame, 

 Roberts table and Dorffel's sets. Then there are the War Office 

 cards, Rumble's gelatine discs and the double lamps. Each lamp 

 is like a signal one, but instead of only white, red and green lights 

 it has about a dozen. The examiner takes one lamp ; the candi- 

 date is given the other ; the former turns on a coloured sector, 

 the latter has to shew a similar one. No questions are asked and 

 no colours are mentioned. 



Stilling used coloured cards, the colours dark and light 

 green alternately being in numerous (357) small squares each 

 bounded by black lines, a checker pattern. On the card was a 

 letter in red squares, the red being equal in intensity to the 

 light green. The different shades of green with the black 

 edging were said to baffle the colour-blind who failed to see the 

 red letter. 



Edridge Green uses a lantern with seven coloured glasses 

 and atmospheric effects can be produced by the ingenious 

 addition of six modifying glasses, four neutral to suggest 

 varying degrees of fog, one ground to represent mist and a 

 ribbed one pretending rain. 



