THE ESSEX FIELD CLUi;. 187 



rays ; so that it is customary to speak of them as lieing " colour-blind." Typical 

 cases are recorded, as those of Dr. John Dalton, of Manchester, the founder of 

 the atomic theory in chemistry ; Professor William Pole, F.R.S., the eminent 

 engineer, who, as a scientific man, took pains to compare his colour sensations 

 with other persons possessing normal sight, and described his own case in a most 

 instructive paper communicated, April, 1859, to the Ro)-al Society. 



The speaker produced his own certificate : " Colour \'ision. Normal " — given 

 him after going through the tests applied in the Anthropometric Laborator}', at 

 the recent meeting of the British Association in Nottingham. This, together 

 with the fact that for twenty years he had been engaged in a colour factory 

 without challenge of his capability of matching tints, proved his capacity for 

 undertaking the examination of others, and for many years he had been in the 

 habit of so doing when opportunities were presented. He knew a score or more 

 of well-pronounced cases amongst his male friends, but confessed that hitherto he 

 had failed in finding a single instance of colour blindness in woman, and it was 

 here that he desired the aid of his lady friends to search for this defect amongst 

 their acquaintances. The published statistics proved its rarity — only about four 

 in a thousand — but he would like to hear of a genuine case, and said that no 

 names need be mentioned. 



Railwa}' guards, engine drivers, firemen and signalmen were now periodically 

 examined, and no officer in the Royal Navy or Mercantile Marine was appointed 

 or promoted until he had satisfactorily undergone the imposed tests. The nature 

 of these tests was then described : — Holmgren's wool test applied in two ways : 

 First, the patient is requested /« i^Ar/ ow;", say, all th? greens from a mixed pile 

 of coloured hanks ; then to iiulc/i one or more samples given as patterns. Rail- 

 way and nautical men were tried with lanterns and shi "ting glasses at various 

 distances. Dr. George Wilson, of Edinburgh, whose treatise on "Colour- 

 Blindness," 1855, first awakened public attention to the necessity for such tests, 

 used a multi-coloured fan or bundle of dyed plume?. Clerk Maxwell's colour 

 top had been used to measure the extent of defects. Dr. Jeaffreson's rotating 

 disc was used to match an indicated sample ; the polariscope and spectroscope 

 were sometimes emploj-ed, and other expedients enumerated in the Royal 

 Societ3''s 1892 " Report of the Committee on Colour-Vision." It was nut 

 always safe to rel}' upon a system of naming colours, for everybody did 

 not know terra cotta, turquoise, purple, russet, or lavender, nor the best 

 of us where blue ends and violet begins. The lecturer found a pair 

 of silk tassels, one of iron grej' and the other bright green, very useful as a 

 preliminary test. Most colour-blind persons hesitated immediatel}', seeing no 

 difference. The iron grey was sometimes called " crimson," and Professor Pole's 

 experience helped us with an explanation, for he always saw the extreme red, or 

 crimson, band of the solar spectrum as a neutral grey. Dr. J. H. Gladstone had 

 published the fact tha' he could not distinguish certain shades of blue and green. 

 The speaker knew a person to whom red and black were alike ; another who 

 could not see berries on the holly, or any difference, even, between a grass lawn 

 and gravel j)ath ; a bookbinder, who often had bound in violet to match a series 

 in brown ; an artist, who was obliged to have his paints mixed for him, or take 

 particular notice of the labels on his colour capsules. The late J. R. Herbert, 

 R.A., as well as Mulready, were known to be colour-blind late in life, probably by 

 the lenses or humours of the eye becoming yellow by age, and misleading them 

 on to excessive indulgence in blue. Instances might be multiplied ; l)ut the fact 



