390 Report of the Committee on Colour-Vision. 



have appeared as only incompletely colour-blind ; and others 

 where a person was at one time incompletely colour-blind in the 

 fullest sense of the word, whilst at another only feeble colour- 

 sense could be shown. In such cases the record should state, 

 in addition, 'incomplete colour-blindness,' approaching complete 

 red or green, or incomplete colour-blindness of slight degree, &c. 



•'The same strict rule should be applied to those already em- 

 ployed as to those seeking service, and all should be discharged 

 who show any lack of colour-perception. This would certainly 

 most fully protect the railroad service from danger. Such a 

 general law, however, has its difficulties, especially as we must 

 recognise, in respect to the danger of confounding the signals, a 

 great difference between complete colour-blindness and a feeble 

 colour-perception. The different cases of incomplete colour- 

 blindness vary also in degree. To draw a line here, and say before- 

 hand who shall be dismissed and who retained, will be as easy 

 in regard to the first as difficult in reference to the latter ; 

 for we are convinced that every case of complete colour-blind- 

 ness of both kinds, as well as every case of incomplete of the 

 higher degrees, should be immediately dismissed. But, as 

 regards those who may be retained, it is clear that the first 

 question concerns those who, at the time of the trial, were 

 regarded in the diagnosis only as having a feeble chromatic 

 sense, and then those who in the first test merely confound grey 

 with the sample-colour. But we do not venture to lay this down 

 as a principle ; for, if it should be proved that these individuals 

 can generally distinguish the light of coloured lanterns with 

 sufficient accuracy, this does not prove that it is so in every 

 case, and especially not at every distance such as are required in 

 the service. This is why we know nothing better to advise than 

 to refer all such cases to competent specialists, as long as the 

 transition period of which we have spoken lasts. 



" It may be asked, How will the specialists themselves 

 proceed ? To answer this, however, would require a much more 

 extended scientific discussion of the various methods than we 

 have proposed here to make. We would only give some hints. 

 A specialist who is familiar with this subject has all known 

 methods at his disposition ; and, if these fail, he need but invent 

 others. As. however, I have been in the position of the specialist 

 in reference to the reform on the railroads of Sweden, I will 

 here say how I have proceeded. 



44 In the examination of doubtful cases submitted to my 

 judgment, I determined according to several of the methods 

 mentioned in one of the preceding chapters. In general, these 

 persons were all subjected to a trial according to the methods 

 of Seebeck and Maxwell, and an examination by means of 

 the visual perimeter and of coloured shadows, as well as the 

 lanterns of my invention and coloured glasses. These last means 

 have capacity especially in view; and they are very suitable for 

 the object, when it is desired to investigate those who have 



