Ill ANN! AI. OF SCIKXTIF1C DISCOVERY. 



continue,! errors of a similar kind led my friends to suspect that my eyesight 

 .left cti\e; '"'t l myself ronld not comprehend this, insisting that I saw 

 rs clearly enough, and only mistook their names. 



"I was articled to a civil engineer, and had to go through many years' 

 practice in making drawings of the kind connected with this profession. 

 The>e arc frequently colored, and I recollect often being obliged to ask, in 

 copying a drawing, what colors I ought to use; but these difficulties left no 

 permanent impression, and up to a mature age I had no suspicion that my 

 vision was different from that of other people. I frequently made mistakes, 

 and noticed many circumstances in regard to colors which temporarily per- 

 plexed me. I recollect, in particular, having wondered why the beautiful 

 rose light of sunset on the Alps, which threw my friends into raptures, 

 -eemed all a delusion to me. I still, however, adhered to my first opinion, 

 that I was only at fault in regard to the names of colors, and not as to the, 

 idea of them; and this opinion was strengthened by observing that the 

 persons who were attempting to point out my mistakes often disputed 

 among themselves as to what certain hues of color ought to be called." Mr. 

 Pole adds that he was nearly thirty years of age when a glaring blunder 

 obliged him to investigate his case closely, and led to the conclusion that he 

 was really color-blind. 



All color-blind persons do not seem to make exactly the same mistakes, 

 or see colors in the same way; and there are, no doubt, man} 7 minor defects 

 in appreciating, remembering, or comparing colors which are sufficiently 

 common, and which may be supcradded to the true defect, that of the 

 optic being insensible to the stimulus of pure red light. It has been asserted 

 by Dr. Wilson, the author of an elaborate work on the subject, that as large 

 a proportion as one person in every eighteen is color-blind in some marked 

 degree, and that one in every fifty-five confounds red with green. Certainly 

 the number is large, for even* inquiry brings out several cases; but, as Sir 

 John Herschel remarks, were the average anything like this, it seems incon- 

 ceivable that the existence of the defect should not be one of vulgar noto- 

 riety, or that it should strike almost all uneducated persons, when told of it, 

 as something approaching to absurdity. He also remarks, that if one 

 soldier out of every fifty-five were unable to distinguish a scarlet coat from 

 green grass, the result would involve grave inconveniences, that must have 

 attracted notice. Perhaps the fact that a difference of tint is recognixed, 

 although the eye of the color-blind person docs not appreciate any differ- 

 ence of color, when red, green, and other colors are compared together, and 

 that every one is educated to call certain things by certain names, whether 

 he understands the true meaning of the name or not, may help to explain 

 both the slowness of the defective sight to discover its own peculiarity, and 

 the unwillingness of the person of ordinary vision to admit that his neigh- 

 bor really does not see as red what he agrees to call red. 



There is, however, another consideration that this curious subject leads to. 

 It is known that out of every 10,000 rays issuing from the sun, and pene- 

 trating spare at the calculated rate of 200,000 miles in each second of time, 

 about one-tmh parr is altogether lost and absorbed in passing through the 

 atmosphere, and never reaches the outer envelop of the human eye. It is 

 iiown that of the rays that proceed from the sun, some produce light, 

 some heat, and some a peculiar kind of chemical action to which the mar- 

 s of photography an> due. Of these, only the light rays are appreciated 

 specially by Hie eye, aliliough liie others are certainly quite as important in 



