Report of the Committee on Colour-Vision. 299 



The second standard skein is light pnrple or pink, and its 

 complementary colour is a green in the spectrum X 5100. The 

 colour is diluted with about 40 per cent, of white. The third 

 test-skein has a colour corresponding with a red of the spectrum 

 (X 6330) diluted with 18 per cent, of white. 



Should an accident happen at any time to the standard sealed 

 pattern skeins, the exact hues can be reproduced from the spectrum 

 by a reference to these numbers. The Committee cannot conceal 

 from themselves the fact that the wools are apt to deteriorate 

 with use, both by the constant handling and also, to some extent, 

 by light. In the test as carried out by Holmgren there is but 

 little doubt that almost as much information is conveyed to the 

 examiner by the way in which the different skeins are picked up 

 to match the test-skein as by the absolute matching itself, and 

 this procedure involves handling them and also exposure to light. 

 The assortment of wools which is used in practical testing should 

 therefore be renewed from time to time. 



In Jeaffresou's form of this test, which is given in Appendix IV, Jeaffreson's 

 page 392, the handling of the colours is avoided, the match being tesfc - 

 made as there described. The hesitation evinced by the colour- 

 blind in matching the test-colouris,in this instrument, also, of great 

 utility to the examiner; moreover, it has been found practically 

 that as many, or even more persons can be examined in a given 

 time by it than by the original plan. The Committee are there- 

 fore of opinion that this modification may be admitted if 

 desired by the examiner. 



These wool-tests will detect red-, green-, and violet-blindness, 

 and all other forms of congenital defective colour-vision. The 

 matches of colours will indicate to the examiner the character 

 and extent of the defect. 



In cases of appeal the examinations should take a wider range. Examination 

 The test with the spectroscope is decisive, and in Appendix V. on appeal, 

 is described a method of applying it which the Committee think 

 may be convenient and satisfactory. 



All tests in which the wools are suspended from a bar, even Tests to be 

 though the test-skeins may be of proper colour and tone, should avoided, 

 bs avoided, since the order of arrangement might be ascertained 

 by some means or another by those who are tested. It is quite 

 true that the order might be changed; but in an examination 

 of this character, where large numbers may be under trial, any 

 frequent changing of the order would be impracticable, and 

 hence there would be no security that the test was efficient. The 

 same objection applies to all diagrams of colours which the 

 examinees are required to match with standard colours. Coaching 

 here is even more easily carried out than with the suspended 

 wools, since the diagrams are in the market, and the tints cannot 

 be changed in position. 



There are some other efficient tests that are less adapted for Other tests, 

 examining large bodies of men than the wool-tests, but which 

 may be well applied to demonstrate the presence of colour- 



