286 Mr, Tomlinson on the Theory of [Oct. 



dental and complementary colours is, that they only apply 

 to those cases where the retina being impressed in a some- 

 what fatiguing manner by the primitive colour seeks relief, 

 as they say, in the accidental or complementary tint. Thus, 

 it is stated, by way of illustration, that when the eye is fixed 

 for some time on a coloured object, a red wafer, for instance, 

 " the part of the retina on which the red rays fall is strongly 

 excited by their continued action. Its sensibility to red 

 light must, therefore, be diminished, in the same manner 

 as the palate, when long accustomed to a particular taste, 

 ceases to feel its impression."* I cannot admit this reason- 

 ing ; for, I have already, in my two previous papers on this 

 subject, shewn, by a variety of experiments, that the primi- 

 tive and complementary colours may be seen at once, readily 

 and distinctly, by means of the coloured solutions on mer- 

 cury, as also by means of the perichromascope.f I shall, 

 hereafter, state other modes of observation by which these 

 colours may be instantaneously seen ; and I must now state, 

 most distinctly, my impression, that in order to observe an 

 accidental or complementary colour, it is not necessary 

 previously to prepare or excite the eye, whether in respect 

 of time or determinate space, by a previous distinct observance 

 of the primitive colour. 



5. Here let me distinguish, and the distinction, is not, I 

 believe, generally adopted or at all attended to, between the 

 terms accidental and complementary: By an accidental colour 

 I mean an impression of a colour, less intense than that pro- 

 duced by the direct impression, and which may or may not 

 be seen when carelessly or inattentively viewing the funda- 

 mental tint ; as, for example, when a red wafer is put into 

 a letter the accidental green is unlooked for, and therefore, 

 generally unseen. But when the red wafer is stedfastly 

 viewed for a sufficient time, a faint green ring begins, and 

 continues to play around the wafer while the eye remains 

 excited. I believe, however, that the mind has great influ- 

 ence in the observance of these ocular spectra,^ as also the 



* Library of Useful Knowledge, Optics, p. 47. 



t Messrs. W. & S. Jones of Holborn, from whom I hare at various times ob- 

 tained much excellent apparatus, inform me that they have prepared this instru- 

 ment for sale. 



X See third note to (6.) 



