NATURAL PHILOSOPHY. 145 



preserving life and carrying on the business of the world. Who can tell 

 whether, in addition to the rays of colored light that together form a beam 

 of white light, four-fifths of which only pass through the atmosphere, there 

 may not have emanated from the sun other rays altogether absorbed and 

 lost; or whether, in entering the human eye, or being received on the retina 

 at the back of the eye, or nuvdc sensible by the optic nerve, there may not 

 Lave been losses and absorptions sufficient to shut out from us, who enjoy 

 what we call perfect vision, some other sources of information? How, in a 

 word, do we who see clearly only three or four colors, and their various 

 combinations, together with their combined white light, how do we know 

 that to beings otherwise organized, the heat or chemical rays, or others 

 we are not aware of, may not give distinct optical impressions? We may 

 meet one person whose sense of hearing is sufficiently acute to enable him 

 to hear plainly the shrill night-cry of the bat, often totally inaudible, while 

 his friend and daily companion cannot perhaps distinguish the noise of the 

 grasshopper or the croaking of frogs, and yet neither of these differs suf- 

 ficiently 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 extraordi- 

 narily 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 color-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 coun- 

 tenance, no brilliant scarlet in the geranium flower; but still he talks of 

 these things as if he saw them, and J\e 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 un- 

 known, either to the subject of them or his friends, even when all are edu- 

 cated and intej^gent, 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 pre- 

 judice, will not believe that their neighbor, intellectually loftier, sees clearly 

 over the fog and malaria of their daily atmosphere. 



In taking leave of the question of color-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 



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