ON ACCIDENTAL OR SUBJECTIVE COLORS. 



PERSISTENCE OF IMAGES.— CONTKAST.—IERADIATION.— DALTONISM, ETC. 



BY THE ABBE MOIGNO. 



Translated for the Smithsonian Institution from the author's " Repertoire d'optique moderne 

 ou Analyse complet des travaux. modernes relatif uuz phtnomenes do la lumierc." 



In order to distinguish clearly between purely objective and subjective colors, 

 of the latter of which it is here proposed to treat, the following definitions should 

 be premised. Objectire colors are those in regard to which the eye is simply 

 an organ of vision, an instrument rather passive than active, perceiving merely 

 an external phenomenon without contributing in any manner to its production. 

 The colors of the solar spectrum, those produced by refraction, those by which 

 bodies manifest themselves to us, &c., are objective colors. Subjective colors are 

 those which are produced, at least in part, by the eye itself, by a certain reaction 

 of the organ of vision under the influence of a first sensation. If, for example, 

 having closely observed in a strong light the yellow covering of a pamphlet, we 

 open it rapidly, the white pages seem overspread with blue light : now, this blue 

 light is evidently nothing real, is no objective color, but a phenomenon un- 

 doubtedly produced in the eye itself — ^.a subjective phenomenon. These latter 

 colors have hence been called accidental and physioJogical. The first term 

 appears to us to be preferable, and we shall usually adopt it ii\ the analysis 

 •which we are about to present of the researches relating to this class of luminous 

 phenomena. 



Reaction of the eye. — In order, first, to give as clear an idea of this remarkable 

 property which the eye possesses of reacting under the impression of a light 

 more or less vivid, and of becoming in some degree active instead of passive, as 

 it previously had been, we shall cite a portion of the letter addressed to Locke 

 by the great Newton, on the images occasioned in the eye by the action of the 

 solar light: "I have made on myself, and at the peril of my sight, the experi- 

 ment which you mention, and Avhich occurs in Mr. Boyle's book on colors. I 

 practiced it in the following manner : Having looked with the right eye, 

 for a very short time, at the image of the sun reflected from a mirror, I then 

 turned my eye towards an obscure corner of the apartment, and closing the eye- 

 lid observed the imjiression which resulted — that is to say, the colored circle 

 which surrounded the image of the sun, and which, growing weaker by degrees, 

 finally disappeared. I repeated this act a second and third time. At the third 

 repetition, when the luminous image and the colors which surrounded it were 

 rapidly disappearing, and while my attention was concentrated in the expectation 

 that I should completely lose sight of them, I saw them, with no little surprise, 

 again make their appearance and gradually become as vivid and strong as they 

 had been at the moment when I ceased contemplating the sun. * * * I 

 was obliged, in order to recover the use of my eyes, to confine myself in a 

 darkened apartment for three whole days, nor did I perfectly recover my sight 

 but by wholly abstaining from the view of all brilliant objects."^ 



This firct and a thousand others abundantly prove that when the portion of 

 the retina, excited by the presence of a luminous object, is suddenly withdrawn 

 from that action, the impression produced by the object does not immediately 



