. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. VISION. 1439 combination of crown and flint glass. He supposed the mean refractive power of flint glass, as compared to crown glass, to be 158 to 153; Fraiinhofer states it to be IG-t to 153. The prismatic dispersion in English flint glass is li times, but in Fraunhofer's, it is twice as great as in crown glass. Such are the chief facts concerning light, •which bear reference to vision: to the con- sideration of the physiology of which we now proceed. Phenomena of Vision. — The special function with which the retina is e
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. VISION. 1439 combination of crown and flint glass. He supposed the mean refractive power of flint glass, as compared to crown glass, to be 158 to 153; Fraiinhofer states it to be IG-t to 153. The prismatic dispersion in English flint glass is li times, but in Fraunhofer's, it is twice as great as in crown glass. Such are the chief facts concerning light, •which bear reference to vision: to the con- sideration of the physiology of which we now proceed. Phenomena of Vision. — The special function with which the retina is endowed being the perception of light, a marvellous range of phenomena is open to the inquirer. It is indeed a wonderful thing to have ascertained beyond doubt, that in perceiving the tint of the scarlet geranium our eves are affected by undulations recurring four hundred and eighty- two millions of millions of times in a second ; that before we can appreciate the tint of the yellow blossoms of the gorse or laburnum, five hundred and forty-two millions of mil- lions of vibrations must have taken place ; and that to discriminate the colour of the violet, not less than seven hundred and seven millions of millions of movements must have been communicated to the fibrillae of our re- tinas ! Whilst such facts almost transcend the powers of human conception, their esta- blishment is a striking triumph of human in- tellect. But how great ought to be our admiration of that Omnipotence which has endowed the eye \\ith the gift, not merely of appreciating one colour, but of distinguishing, in all their shades, the inexpressibly compli- cated vibrations which mark the hues of a parterre of flowers, and characterise the gor- geous plumage of the birds which give anima- tion to a tropical forest. The sense of sight, in its ordinary acceptation, may be defined as the recognition by the mind of certain im- pressions made upon the retina, and commu- nicated through the medium of the optic n
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