Unequal affinities of the organ may explain thus various defects of vision with regard to colours.----a» imperfect eye for colours is hardly, perhaps, less common than a bad ear for musical sounds. We were some years ago introduced to an intelligent gentlemanly man, about fifty years at age, high in office at the East India House, who never had been able to distinguish tiny colour sufficiently to name it, nor designate such otherwise than as comparatively light or dark, and who used to refer to his daughter, whose eyes were excellent, for their nominal distinctions. He used spectacles, but his eyes were not otherwise defective.

In the Philotophicai Transaction* for 1738, is an account of persons to whom all objects appeared red after having eaten henbane roots.

In the same journal for 1777, page 250, one Harris is mra-tioned who could not tell black from while. He had two brothers equally defective, one of whom mistook orange for green.

Again {Phil. Trans. 1778, p. 613), to another person full reds and full green* appeared alike, but yellows and dark-Mum were very nicely distinguished.

It is remarkable that in those cases of defective vision in which the eye is insensible to either of the primary colours, the party so defective confounds with, or regards such colours as its opposite or contrasting colour.

This phenomenon is easily explained upon our principle of vision and colours, and the fact we have demonstrated by proving that each colour contains virtually all the others: whence, if the eye be insensible to red, a red object even will appear to be green, and so of other cases. The rationale of a good or bad eye for colours rests upon the same ground, which depends upon the health or infirmity of the organ; and there can be no doubt that cultivation may very greatly improve the sensibility of the eye with regard to colours, as exercise strengthens the powers of the mind, and increases the health, vigour, and dexterity of the body: this is evident in the case of myopes, or the short-sighted, in whom the eve for colours is commonly deficient.

Inasmuch as a man is deficient in any sense, he is still unborn; whence those who are defective of vision are unconscious of, and never suspect, their own incapacity; accordingly the want of a good eye has not prevented some very eminent men from attaining high reputation in painting in spite of defective colouring; nor has it prevented others from investigating and writing on colours: nevertheless, it is probable that much discordance in the theory of colours may have arisen upon this foundation. A late professor of painting expresses himself upon this subject like one bom blind, or who had never seen colours; and many natural philosophers appear to have been remarkably deficient in this sense. Newton confesses that his eye for distinguishing colours was not very critical, and that he availed himself of assistance in this respect. Mr. Dallon could not distinguish blue from pink by day light.+ Professor Sanderson, who was born, or very early became, blind, delivered lectures upon light and colours; and Dr. Priestly mentions an artist living in Edinburgh whose companions " have, by putting his colours out of the order in which he keeps them, sometimes made him give a gentleman a green beard, and paint a beautiful young lady with a pair of blue cheeks!"

• Optiet, Prop. III. Prob, I. p. 110. + Manchester Mem. Vol. XXVIII.

It is in like manner to be suspected that an eye for forms as much wanting in some men as an eye for colours, or an ear for musical Bounds is in others; and that hence the efforts of some artists in drawing and composing are destitute of grace, harmony, beauty, and expression, which nevertheless flowel with the ease of nature from the hand of a Correggio, Guide Raphael, or Dominichino: and, in all likelihood, then is in every man some deficiency of sense combined with some de-terminate excellence upon which peculiarity of talent in art and diversity of judgment and character depend.