Proceedings of the Royal Institution. 403 



1822, it presented the appearance of a pinniform fibrous tissue, so 

 arranged, that small changes in the tension of the larger fibres from 

 which the parallel ones diverged would produce an immediate and 

 general change in the proximity, but not in the parallelism of the 

 smaller fibres ; if the production of compensatory spectra lie in this 

 membrane, confusion in the direction of the fibres will account for 

 the imperfect vision of those who are insensible to perceptions of 

 colour, and distinguish objects by the quantity, instead of the quality 

 of the light which they reflect ; or, when less imperfect, are sensible 

 of certain colours only. This may account for the pictures of Paul 

 Brill being always green, and those of Both foxy. The striated 

 structure would serve also to explain why, whilst the eye still views a 

 red wafer, a green fringe surrounds the disk, though the eye be fixed 

 on a spot in the centre of the wafer ; — ^'tis the intermediate fibres, 

 which, partially excited after long gazing, extend beyond the imping- 

 ing image to those fibres which are in repose. It is perhaps taking 

 too great a license, to conjecture thus from analogy, upon a subject 

 capable certainly to some extent of investigation, but which it does 

 not closely follow in every point. The physical differences of coloured 

 rays are known ; their illuminating, heating, magnetising, and che- 

 mical powers differ. These, or some of these, appear to possess 

 different stimulating qualities ; and, acting upon so sensible an organ 

 as that of vision, may account for effects whilst vitaUty exists, which 

 cannot be readily perceived in the delicate organization of many of 

 the parts after death. Besides the complementary spectra of colour, 

 white and black mutually affect the organ with contrary spectra — as 

 if pure light of a certain intensity only could keep the eye in repose. 

 Mr. Brockedon thought a different compensatory power might 

 exist for this in the collection or expulsion of the pigmentum nigrum 

 which lies behind, and in immediate contact with the membrane of 

 Dr. Jacob, where the fibres are excited to a change in their proximity; 

 —it is evident, that a compensatory power for quantity of light exists 

 independent of the power which governs images of coloured, or quali- 

 ties of light, as those, who are insensible to colour, are sensible of 

 form, and of the compensatory spectra of black and white. Mr. 

 Brockedon expressed his regret, that the remarks which he had to 

 offer were so crude, but he offered them as stimulants to the investi- 

 gations of others upon a subject of which so little is known, but wliich 



