334 MEMOIR OF GEOKGE WILSON. CHAP. VIII. 



the title, ' On the prevalence of Chromato-pseudopsis, or Colour- 

 blindness ; ' but as the practical relations of colour-blindness 

 could not be fully discussed in this professional periodical, Dr. 

 Wilson communicated to the Royal Scottish Society of Arts an 

 important paper ' On Railway and Ship Signals in relation to 

 Colour-blindness/ This communication was read January 8, 

 1855, and it speaks well for the liberality, not less than the dis- 

 cernment of this distinguished Society, that, being deeply im- 

 pressed with the importance of the facts stated by Dr. Wilson, 

 they circulated at their own expense, copies of the paper among 

 the railway companies, and, unsolicited, placed at Dr. Wilson's 

 disposal a grant of money to be expended on the inquiry. 



" The lights selected by the Admiralty to be carried by sea- 

 going vessels to prevent collision, are green on the starboard 

 side ; red on the port side. Now these are the colours most 

 liable to be confounded by the colour-blind ; and a very singu- 

 lar fact came to the knowledge of Dr. Wilson in the course of 

 his inquiries : of a Board amongst whose duties was that of in- 

 vestigating the use of coloured lights as signals, it chanced that 

 of five members, two were colour-blind ; and one day a clerk- 

 unconscious of his defect copied a letter in red ink, thinking it 

 was black ! 



" Red and green are well known to railway travellers, as in- 

 dicating, red, danger green, simply caution. Thus, both by 

 sea and by land, these, the colours most frequently confounded 

 by the colour-blind, are the very colours selected as important 

 signals ! Yet how essential to safety is their due appreciation ! 



" Dr. Wilson enters at great length into the consideration of 

 the question in all its bearings, and points out the necessity of 

 signal-men being tested as to their appreciation of colour, 

 describing minutely the course to be pursued, which would cer- 

 tainly lead to the detection of those deficient in this qualifica- 

 tion ; and as an additional measure of precaution, Dr. Wilson 

 dwells on the necessity of employing the elements of form and 

 number, as well as colour, in railway signals. 



" Though less generally adopted than could be desired, these 

 suggestions have not fallen barren to the ground. Dr. Brinton, 

 who examines candidates for railway appointments in India, 



