of the grasshopper, or the croaking of frogs, and yet neither of these differs sufficiently from the generality of mankind to attract attention, and both may pass through life without finding out their differences in organization, or knowing that the sense of hearing of either is peculiar. So undoubtedly it is with light. There may be some endowed with visual powers extraordinarily acute, seeing clearly what is generally altogether invisible; and this may have reference to light generally, or to any of the various parts of which a complete sunbeam is composed. Such persons may habitually see what few others ever see, and yet be altogether unaware of their powers, as the rest of the world would be of their own deficiency.
The case of the colour-blind person is the converse. He sees, it is true, no green in the fields, or on the trees, no shade of pink mantling in the countenance, no brilliant scarlet in the geranium flower, but still he talks of these things as if he saw them, and he believes he does see them, until by a long process of investigation he finds out that the idea he receives from them is very different from that received by his fellows. He often, however, lives on for years, and many have certainly lived out their lives without guessing at their deficiency.
These results of physical defects of certain kinds remaining totally unknown, either to the subject of them or his friends, even when all are educated and intelligent, are certainly very curious; but it will readily be seen that they are inevitable in the present development of our faculties. In almost everything, whether moral or intellectual, we measure our fellows by our own standard. He whose faculties are powerful, and whose intellect is clear, looks over the cloud that hovers over lower natures, and wonders why they, too, will not see truth and right as he sees them. Those, on the other hand, who dwell below among the mists of error and the trammels of prejudice, will not believe that their neighbour, intellectually loftier, sees clearly over the fog and malaria of their daily atmosphere.
In taking leave of the question of colour blindness, it should be mentioned that hitherto no case has been recorded in which this defect extends to any other ray than the red.
There seems no reason for this, and possibly, if they were looked for, cases might be found in which the insensibility of the optic nerve had reference to the blue instead of the red ray—the least instead of the most refrangible part of the beam of light. It would also be well worth the trial if those who have any reason to suppose that they enjoy a superiority of vision would determine by actual experiment the extent of their unusual powers, and learn whether they refer to an optical appreciation of the chemical or heat rays, or show any modification of the solar spectrum by enlargement or otherwise.
Lastly, it would be well, when children show an unusual difficulty in describing colours, to try by some such experiments as those here related whether any defect of colour blindness exists or not. It would clearly be undesirable that such children as have this defect should waste time in learning accomplishments or professions which they must always be unable
