insensibility to the impressions of certain colours. 135 



Prof. Wartmann's memoir in which he has mistaken my opi- 

 nion, is the following: — 



" Tous les physiciens savent que les limites des sons per- 

 ceptibles varient d'une oreille a I'autre; c'est ce que Wollaston 

 et Chladni ont irrecusablement demontre. Sir D. Brewster* 

 suppose, par analogie, que dans le cas de DaUonisme I'oeil 

 n'est pas impressionne par les couleurs de I'une des extremites 

 du spectre. L'insensibilite de quelques yeux aux faibles im- 

 pressions lumineuses s'explique, dit il, en ce que la retine par 

 son organisation naturelle, ou par quelque cause accidentelle, 

 pent etre moins delicate ou nioins susceptible des impressions 

 de la lumiere chez une personne que chez une autre, sans que 

 les facultes visuelles en soient affaiblies d'une maniere conco- 

 mitantef." 



The opinion contained in the preceding extract was given 

 in December 1821, and is more an illustration from analogy, 

 than an explanation of the phaenomenon. It differs, indeed, 

 very little from that previously given by Dr. Thomas Young, 

 who attributes colour blindness to " the absence or paralysis 

 of those fibres of the retina which are calculated to perceive 

 red ;" and it differs nearly as little from the opinion afterwards 

 given by Sir John Herschelij:, Dr. Elliotson, and Prof. Wart- 

 mann himself, that colour blindness arises ^^from a defect in 

 the sensorium." Now Prof. Wartmann observes, in reference 

 to my explanation as given above, "// me semble que cettethS- 

 orie manque des preuves." True, — it not only wants proofs, but 

 it is incapable of being proved, and so is the theory of a defect 

 in the sensorium ; and so is Dr. Young's theory of a want of 

 proper fibres, or of a paralysis of existing fibres. All these 

 theories, indeed, are mere conjectures, and Dr. Dalton's hypo- 

 thesis of a blue vitreous humour is the only one capable of 

 being proved or disproved. 



As I know nothing about the sefisorium, or about its con- 

 nexion with, or mode of operation upon, the nerves of sensa- 

 tion, I shall leave the discussion of the merits of the new 

 theory to those who feel themselves qualified for so arduous a 

 task ; I shall content myself with bringing forward some im- 

 portant and, I believe, new facts, which will at least illustrate, 

 if they do not confirm, the opinion which I have expressed 

 respecting the cause of colour blindness. 



In the sentence immediately preceding the one above quoted 

 by Prof. Wartmann, I state that " I have lately ascertained 

 that some eyes which perform all the functions of vision in the 



• Edln. Phil. Journal, vol. vi, p. 141, Jan. 1822. 



t Mevioire sur le Daltonisme, par Elie Wartmann, Prof, de Physique a 

 I'Academie de Lausanne, &c. &c. Geneve 1844, 54 pp. 

 X Treatise on Light, Art. 507. 



