REPORT ON COLOUR-VISION.* THE Committee on Colour-Vision appointed by the
Royal Society has, after two years' work, produced an interesting- and instructive Report. This Report has been presented to- the Board of Trade, and laid upon the table in both Houses of Parliament. Before discussing its contents, a few wordu explanatory of the singular subject to which it relates may be- usefully introduced.
About ninety-six out of every hundred men see coloured objects and coloured lights in what is virtually the same way; in the case of women, the per-centage of those who possess normal colour-vision is very much greater. The defect of the minority is commonly called colour-blindness,----it may be better- described as imperfect colour-vision. One of the ways of studying this peculiarity consists in confronting the in- dividuals to be tested with a spectrum, the sheaf or band of coloured rays obtained by decomposing white light by means of a prism. These rays succeed one another in ordered sequence, beginning with red, and passing through orange,. yellow, yellow-green, green, green-blue, and blue, to violet. In some cases of imperfect colour-vision, the spectrum appears shortened at one end or the other, more commonly the red end being affected. But in the majority of cases, the perception of a great part either of the red region or of the green region is, very imperfect, so that near the middle of the spectrum a grey or white band takes the place of the green or greenish-blue there visible to the normal eye. The position of this neutral band, and- the degree of shortening of the spectrum, may be exactly measured by means of the fixed black lines in the solar spectrum. The spectrum of an electric arc-light may be- advantageously used in testing colour-vision in another way. Patches of coloured light from definite parts of such a spectrum may be thrown singly or together on a screen, and the examinee may be asked to make matches with them. Thus, for example, it is found that, even with normal-sighted persons, the quantities of red and green light which must be combined to make a yellow corresponding to a standard yellow, are not absolutely the same in all cases. But when colour-vision is decidedly imperfect, these differences are much greater ; while mistakes in matching the coloured lights are of a different order, some individuals regarding a particular green light as identical with white, and other individuals not perceiving the red constituent in a mixture of red and white light. There are, then, degrees in the extent,. and differences in the kind, of colour-blindness in those who suffer from this singular affection. Colour-blindness may also arise from several causes. Usually it is congenital, and cannot be cured ; sometimes it is induced by excessive smoking of strong tobacco, or by disease or injury, and may then prove to be temporary.
As persons suffering from defective colour-vision of pro- nounced character cannot distinguish between the red and
green parts of the bright spectrum of the electric light, it is obvious that they will likewise confound the red and green, and even the white, signals used on railways and at sea ; in hazy and foggy weather, such confusion will occur also in the • Royal Sociny : Brport of tits Cc•nwnit.00 un Vision. 1592.
case of persons whose colour-vision is but slightly defective. Such individuals lose the power of discriminating between colours in an obscuring atmosphere long before the normal- sighted are affected.
After these prefatory remarks, we may enter upon the dis- cussion of the Report before us. That part of this document which contains the chief outcome of the inquiry, is wisely put in the forefront, and occupies only two pages. It describes the appointment and constitution of the Committee ; gives the names of the methods and apparatus for detecting colour- blindness which it has examined; mentions the officials and experts whose evidence it has taken ; and thanks its Secre- tary, Captain Abney, for his determinations of colour- constants, his registrations of colours, and his examinations, by spectral methods, of particular cases of defective colour- vision. It concludes with twelve recommendations of an entirely practical character. The Committee recommends the compulsory testing for colour-and-form vision, and for the names of colours, of all candidates for certain employments to be subsequently scheduled by the Board of Trade. it advises the use of Holmgren's wool-test, supplemented when needful by other methods Other recommendations relate to certificates, to examiners, and to periodical inspections and reports. The eleventh recommendation relates to the general adoption for railway and ship lights of the pattern green and red glasses of the Royal Navy. The last recommendation stands thus :— "That in judicial inquiries as to collisions or accidents, wit- nesses giving evidence as to the nature or position of coloured signals or lights should be themselves tested for colour and form vision." We feel sure that if th;s testing had not been ignored, the cause of many accidents at sea or on the rail would have been revealed. For it is remarkable how few collisions or disasters have been traced to colour-blindness. Two or three are mentioned in the Report before us : several others are described in Dr. Edridge Green's book on Colour- Blindness (pp. 221-232). But the paucity of material of this kind mainly arises from the omission to test witnesses for their appreciation of colour. It is to be hoped that Judges and counsel will not in future ignore this extremely important point.
Two omissions from the Committee's recommendations may be noted. We understand that the Pilot Service is not under the control of the Board of Trade, nor under that of any one central authority. It is desirable that it should be subject to the same uniform system of testing as that recommended in the Report for "certain employments in the mercantile marine and on railways." The second omission which we regret relates to the compulsory testing of boys before they are received to be trained in any institution for the sea. In sup- port of this contention, the evidence of Mr. T. H. Bickerton, of Liverpool (p. 35), is very strong. One paragraph from the evidence of Captain Ma,enab, of the Local Marine Board at Liverpool, may be quoted from p. 59 of the Report :—" With regard to the Indefatigable,' supposing a boy were found to be colour-blind, would the authorities of the ship dismiss him?" "No, he would be quite free to complete his educa- tion." The defective colour-vision of the lad might, it is true. and probably would, be detected later on in his career ; but the omission of a preliminary examination involves considerable hardship to him, for he will have been trained for an occupa- tion for which he is clearly unfit. Perhaps the Committee's second recommendation, as to the testing of candidates for certain employments in the mercantile marine and on railways, was intended to include such cases as those to which reference has just been made.
The remaining contents of the volume under review may be arranged under four heads. First we have an introductory account of defective colour-vision, including a description of its several varieties, and of the various theories of colour- perception. Then there are paragraphs discussing the colour- blindness induced by tobacco, and by progressive atrophy , of the optic nerve ; in both of these cases the defect is confined to the central portion of the retina, where the sensations perceived are those of blue and of white only. Statistics of colour-blindness follow, and then some remarks as to its results and its dangers. The results of the spectral analysis of the various green and red signal-glasses employed on different railways, are exhibited in a table, and then the most suitable colours are investigated. The last seven pages of this section of the volume are devoted to the consideration of tests. Those of the Board of Trade are misleading and ineffective. Their test-cards and coloured glasses can be o1- tamed from dealers, and candidates who are colour-blind can be taught, by previous coaching, to name the colours correctly, judging not by their hue, but by their relative brightness. The railway-tests vary in kind, and on some lines are so unsatis- factory that a colour-blind person was passed in the presence of the Committee by two of the railway examiners. Holm- gren's wool-test, conducted exactly as Holmgren directs, is that recommended by the Committee, but Jeaffreson's form of the test, in which the handling of the coloured wools is avoided, is regarded as equally available. The obvious tests afforded by the use of actual railway-lamps are condemned as unsafe (p. 20). The question of the naming of colours is next considered. The statement is made that "it is in evidence that in navigation it is often requisite that the look-out man should, without a moment's delay, pass on to the officer in charge the name of the colour of a light, and that hesitation, whether caused by true colour-ignorance or by want of knowledge of English terms, might involve disaster." In consequence, no man should be accepted as a look-out unless be were found to be not only possessed of adequate colour-vision, but also capable of naming correctly the signal-colours.
We now come to the second part,—namely, the evidence taken by the Committee. It includes that of the colour-blind themselves ; of Board of Trade, steamship, and railway officers ; of surgeons and experts ; and of a private instructor in navigation. One of the duties of this coach was to teach the colour-blind how to pass the Board of Trade tests successfully ! We have already referred to a few points brought out by the witnesses who were examined by the Committee, but there are many other matters which, for want of space, we must pass over without notice. The evidence has been well weighed by the Committee, and had a con- siderable share in shaping the recommendations of the Report. But it must not be forgotten that the Committee itself con- ducted many experiments on apparatus and methods for testing colour-vision, and that its conclusions were mainly founded on evidence derived from such sources.
The third part consists of letters, bearing on examinations for colour-blindness, received from Railway and Steamship Companies, as well as from some departments of the public service. Most of these letters reveal the necessity for more serious attention to the subject of colour-blindness, and for more systematic and uniform methods of detecting its occur- rence. One railway official states that "it is not at all an infrequent occurrence to find men coming up, more particularly from the rural districts, quite unable to name the colours (seven are shown to them) correctly, purely from want of education. These men are always rejected." It must be owned that this is hard on the men examined, the great majority of whom see the colours correctly, and need nothing but a few minutes' instruction in colour-nomenclature to pass the test satisfactorily. The apparatus employed by this rail- way is defective ; nor is it just to base a system of testing for colour-vision entirely upon the correct naming of colours.
The last part of this volume contains seven appendices. Of these, the first gives statistics of colour-blindness ; in the second, the Circular of the Board of Trade relating to their colour-tests is reproduced ; the third appendix is devoted to full instructions as to Holmgren's method of testing by means of coloured wools,—this appendix is illustrated by a coloured plate, and occupies more than twelve pages. This full treat- ment of the method is amply justified by its supreme im- portance. If any of our readers are sufficiently interested in the subject, they cannot do better than purchase a set of Holmgren's wools from Messrs. Curry and Pickard, of Great Portland Street, and put their friends through their colour- paces. It is of no use testing ladies, as their colour-vision is rarely defective. But it is amusing to see a colour-blind man matching the standard green skein with a similar green, and then withdrawing it in order that be may substitute a better match in the form of a grey, a pink, or a purple In Appendix TV., Holmgren's wools are shown arranged radially on a disc, as recommended by Dr. Jeaffreson. The next two appendices relate to spectrum-tests and tests for form- vision ; the last page contains a summary of colour-blind cases detected at an examination of railway employes at Swindon.
We have attempted no serious criticism of this Report, but have endeavoured to convey a notion of the ground it covers. It is an extremely valuable document, which the Board of Trade will do well not only to consider but to adopt. The recommendations of a Committee which included many authorities on the subject of colour and colour-vision will, we .doubt not, receive the attention they deserve.
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