If a person with perfect sight will look steadily for a few moments at any object, of one of the three primary colours, whether a lamp or anything else, and then close his eyes, and watch so to speak, with his closed eyes, he will find the object reproduced in a kind of cloudy representation, or rather retained on the eye; but its colour will be changed from the primary to its corresponding (complementary) secondary colour. Thus the impression of a red object will present itself as green; yellow as purple; and blue as orange. Vice versâ, if the object is one of those secondary[A] colours, the reproduction on the retina will be of the corresponding primary colour. In this way, it is quite possible for a man, who has been looking for any length of time at a red light on a railway at night, to remove his eyes for a moment or two; and, on looking again at the lamp, to find that—in the course of the natural relief afforded by the impression on the eye resolving itself into the secondary colour—his sight is for a moment impeded by the floating image (now green instead of red) before his eyes, and the actual lamp (still red) covered, as it were, by the retained figure, so that it appears to be green. This curious effect is no fault of vision, and might easily mislead an engine-driver who, having first actually seen the red light, has, after withdrawing his eyes, immediately afterwards imagined it changed to green or white, in indication of the removal of the obstacle to the progress of his train. In this way, by continual straining of the eye in search of a particular signal, especially at night, with no light beyond that of the glaring furnace of the engine—in itself detrimental to the eyes—it is quite possible that colour-blindness may be acquired, and that a man who was once perfectly able to distinguish the most delicate tints may become insensible to the effects of widely different colours.
Whatever its cause, it is a fact that colour-blindness does exist to a very considerable extent. In Egypt this is so well recognised a fact, that engine-drivers and others employed on railways are obliged to undergo a special examination before they are allowed to proceed to their duties. Many curious stories are told concerning the attempts made by men suffering under this infirmity to escape the penalty of detection; they will often rather run the risk of bringing themselves and others to sudden death in a collision, than lose the coveted post by admitting their defective sight. Sometimes a man will successfully guess at the red, white, and green lamps or flags held before him; but, if the examiner is as astute as the examinee, he will balk his calculations by holding out a cap, or some other article not usually classed among the list of railway signals, and an unguarded 'Red' or 'Green' from the lips of the candidate will send him ruefully off about his business.
Researches lately made in Sweden shew that this peculiar defect of sight is prevalent in that country. Out of two hundred and sixty-six men examined recently by Professor Holmgren, eighteen were found to be colour-blind; and in our own land statistics prove that Englishmen are not free from the infirmity. The late Professor George Wilson, who made a special investigation into the subject in Edinburgh some years ago, stated that out of one thousand one hundred and fifty-four persons of various professions examined in 1852, no less than sixty-five were colour-blind; and of these, twenty-one specially confounded red with green. A gentleman employing a number of men, writing to the Times, states that recently he directed an upholsterer to cover some article of furniture in green leather, and that the man used a skin of bright red leather, not knowing the difference. He could only distinguish colours in their intensity, all appearing to him as different shades of gray.
But instances could easily be multiplied. The practical part of the question is its bearing on the employment of men upon whose sight and power of distinguishing colours many lives are dependent. Engine-drivers and signal-men, railway guards and sailors, often have nothing but a red or green speck of light between the safety and the death of themselves and perhaps hundreds of their fellow-creatures. How many of the 'missing ships' that have set forth in hope, with scores or hundreds of souls on board, and never been heard of again, have gone to their fate through the colour-blindness of the 'look-out,' who can tell? How many disastrous railway collisions have been owing to the same defect on the part of the engine-driver or stoker? The necessity of a rigid examination of all men employed on our railways, in order to ascertain their power of distinguishing the colours of the signals upon which so many lives depend, is being recognised by the directors and other officials. The same precaution ought to be adopted in the case of sailors, and not only once, but frequently. Periodical tests of their eyesight should be made at regular intervals; for in a physical infirmity of this kind, so apt to be overlooked and remain unrecognised even by those who are subject to it, lurk more dangers than in the lack of many other strictly enforced requirements.
FOOTNOTES:
[A] Secondary colours are those which are formed by the combination of any two of the three 'primary' colours; the combinations of secondary colours are called 'tertiary' colours.
[GOLD-MINE EXPERIENCES.]
I was living some years ago in one of our North American provinces, where, for several seasons, I was employed in constructing a railway, which at the time I write is in liquidation, and which I shall call the Swindleville Junction, a name, I trust, sufficiently expressive. The climate did not suit me, neither did the natives; they were much too 'smart' for my fancy, and I was pretty generally always cheated in my dealings among them. In one instance, however, I managed to save myself from being tricked, but I am bound to say that it was from the clutches of a Yankee that I made my escape, for I fully believe that a native operator would never have given me a chance.
Gold had been discovered about thirty miles from the town of Radnor, which was my headquarters, and the miners were making much money by crushing the quartz. Of course the country was soon inundated by prospectors, and numerous holes were opened with varying luck. Curiously enough, the American element did not prevail much in the district, the fact being that the provincials are more than a match for an American even with his own weapons.