1884
THE NEW ZEALAND GAZETTE.
[No. 91]

(9.) In the remarks which follow reference is made to different kinds of colour-blindness (red-blindness and green-blindness), but the Examiner is not required to form any conclusion as to the kind of colour-blindness from which the candidate suffers, and should not offer the candidate any opinion on this point.

All that is required is that the Examiner shall conduct the examination according to the rules laid down, and from the wools selected judge whether the candidate is or is not colour-blind, the nature of his colour-blindness being immaterial.

(10.) The result of every test should be reported to the Marine Department.

All cases of failure should also be reported to the Marine Department, with the pieces of the wools incorrectly selected by the candidate. (See par. 4.)

Holmgren’s Method of Testing for Colour.

The method of testing consists in asking the candidate to select from variously-coloured objects those which appear of the same colour as one which the examiner selects. The most suitable objects and at the same time the most readily obtainable are skeins of wool, which can be procured of almost every desired hue and tone. An advantage of skeins of wool, besides their portability, is that, owing to their want of gloss, they appear of approximately the same tone from whichever side they are viewed. The colours of the skeins to be selected include reds, oranges, yellows, yellowish-greens, pure greens, blue-greens, blues, violets, purples, pinks, browns, and greys. Several shades of each colour, with at least five gradations of each tint, are provided, from the deepest to the lightest greens and greys. Varieties of pinks, blues, and violets, and of light-grey, together with shades of brown, yellow, red, and pink, are well represented. The test-skeins with which the examinees are to compare the other skeins are three in number—(1) a light-green, (2) a pink or pale purple, and (3) a bright-red. These three colours will suffice to indicate approximately the amount and kind of colour-blindness which may exist. The light-green skein, which is a tolerably pure green mixed with a large proportion of white, is chosen as the colour which closely matches the spectrum colour which the red- and green-blind distinguish as white or grey. It is chosen of a pale tint, as it then becomes puzzling to the colour-blind to distinguish its colour by luminosity. A light-grey or drab skein will present the same brightness to him that this pale colour does, and, although he may be trained to distinguish bright colours by their relative luminosities, in the case of these pale varieties he will be unable to do so. The pink or light-purple is chosen for similar reasons, and, in fact, it is nearly a complementary colour to the green. The purple is, according to the Young-Helmholtz theory, a mixture of two fundamental colours, the blue and the red, and as in the green-blind it excites both the blue and red sensations it may be confused with grey, or with a green. In the red-colour-blind it excites in excess the blue sensations mixed with what they call white. A blue or violet may therefore be matched with it.

The method of examination is as follows:—

The wools are placed in a heap on a large table covered by a white cloth or white paper, and in broad daylight. The first test-skein is taken from the pile, and laid far enough away from the others not to be confounded with them during the examination. The person examined is requested to look carefully at the test-skein, and then to select other skeins from the pile most nearly resembling it in colour, and to place them by the side of the sample. At the outset, it is necessary that he should thoroughly understand that he is required to search the heap for the skeins which make an impression on his chromatic sense or sense of colour similar to that made by the test-skein, and quite independently of any name he may give the colour. The examiner should explain that resemblance in every respect is not necessary; that there are no two specimens exactly alike; that the only question is the resemblance of the colour: and that, consequently, the candidate must endeavour to find something similar in shade and something lighter and something darker of the same colour. If the person examined cannot succeed in understanding this by a verbal explanation, resort must be had to action. The examiner should himself pick out the skeins, thereby showing in a practical manner what is meant by a shade, and then restore the whole to the pile, except the sample skein. As it would require too much time to examine every individual in this way it is advisable, when examining large numbers, to instruct them all at once, and to ask them to attentively observe the examination of those preceding them, so as to become more familiar themselves with the process. This saves time, and there is no loss of security, for no one with a defective chromatic sense will be able to find the correct skeins in the heap the more easily from having a moment before seen others looking for and arranging them; he will make the same characteristic mistakes. But the normal observer, on the other hand, will generally accomplish his task much better and more quickly after having seen how it has to be done.

The coloured plate shows the test-colours and some of the mistakes likely to be made by colour-blind people. The colours in the plate are of two characters—

1. The colours for samples (test-colours)—that is, those which the examiner presents to the person examined; and

2. The “confusion-colours”—that is to say, those which the colour-blind may select as matches with the sample.

The first are shown on the plate as horizontal bands, and are distinguished by Roman numerals (I., II.a, and II.b), the second as vertical bands, under the test-colours, and are distinguished by Arabic figures (1, 2, 3, &c.).

As to the similarity between the confusion-colours of the plate and the wools which the colour-blind take from the heap, reliance must be placed simply on the hue, and not on their brightness or degree of colour-saturation. The confusion-colours shown in the plate are only to illustrate the mistakes which the colour-blind may make, and for this purpose they serve perfectly. Having made this explanation, we can pass directly to the test itself. The following are the directions for conducting it, and for making a diagnosis from the results:—

Test I.—The green test-skein which is labelled Test No. I. in the bundle is exhibited to the candidate. This sample is the palest shade (the lightest) of very pure green, which is neither a yellow-green nor a blue-green to the normal eye, but fairly intermediate between the two, or at least not verging upon yellowish-green.

Rule.—The examination must continue until the examinee has placed near the test-skein several other skeins of the same colour, or else, with these or separately, one or more skeins of the class of “confusion-colours” such as 1 to 5 in the plate, or until he has sufficiently proved that he can easily and unerringly distinguish the confusion-colours, or else has given unmistakable proof of a difficulty in accomplishing it.

Diagnosis.—An examinee who places with the test-skein “confusion-colours” such as 1 to 5—that is to say, finds that they resemble the “test-colour”—is colour-blind, whilst if he evinces a manifest disposition to do so though he does not absolutely do so, he has a feeble chromatic sense, or sense of colour.

Remark.—We might have taken more than five colours for “confusion”; but we must remember that we are not taking into consideration every kind of defective colour-sense.

Test II.—The pink or light-purple skein which is labelled No. II.a is shown to the examinee. The colour is midway between the lightest and darkest. It only approaches that given as II.a of the plate, as the colour of the wool is much more brilliant and saturated, and bluer.

Rule.—The trial must be continued until the examinee has placed all or the greater part of the skeins of the same colour near the test-skein, or else, together or separately, several skeins of the “confusion-colours” such as 6–9. If he is colour-blind he will probably select either the light or deep shades of blue and violet, especially the deep (6 and 7), or the light or deep shades of one kind of green or grey inclining to blue (8 and 9).

Test III.—The red skein labelled No. II.b is presented to the examinee. It is necessary to have a vivid red colour, like the red flag used as signals on railways. The colour should be that of II.b of the plate, rather towards yellowish-red.

Rule.—This test should be continued until the person examined has placed beside the test-skein the greater part of the skeins belonging to this hue, or else several “confusion-colours” (10–13).

Remark.—Every case of comparatively complete colour-blindness does not always give precisely the same mistakes. Instances occur of persons who are not completely colour-blind, or of completely colour-blind persons who have been practised in the colours of signals, and who endeavour not to be discovered. They usually confound at least green and brown, but even this does not always happen.

Monochromatic Vision.—The absence of every colour-sensation except one will be recognised by the confusion of all the hues, which will appear to be of the same intensity of light or brightness.

Dr. Joy Jeffries, in his book on colour-blindness, gives a translation of Holmgren’s special directions for conducting the examinations. The examinations to which Holmgren refers were for employés on the Swedish railways, but the remarks which follow are applicable to examinations for officers and seamen in the mercantile marine.

Special Directions for conducting the Test.

The method plays an important part in an examination of this kind, not only from the principles upon which it rests, but also from the manner in which it is used. The best plan for directing how to proceed is by oral instructions and de visu, but here we are obliged to accomplish this by description. Now, this is always defective in some respects, especially if we wish to be brief. What has been said would evidently suffice for an intelligent and experienced physician; but it may not be superfluous to enter still further into detail to provide against any possible difficulties and