xxxiv CONTENTS. 



532. Emmetropic, myopic, hypermetropic, and presbyopic eyes . . 849 



533. The changes observed in the eye during accommodation . . 850 



SECTION III. 



THE MECHANISM OF ACCOMMODATION AND THE MOVEMENTS OF 

 THE PUPIL. 



534. The mechanism for changing the anterior curvature of the lens . 854 

 535. The evidence that such a mechanism does effect the result . . 856 



The Changes in the Pupil. 



536. Circumstances leading to constriction and to dilation of the pupil . 857 



537. Constriction and dilation 858 



538. The nerves supplying the pupil 859 



539. Constriction a reflex act by means of the optic and oculo-motor 



nerves 860 



540. Changes in the pupil through the action of the cervical sympathetic 



nerve 862 



641. The nature of the dilating mechanism 863 



542. Direct action of drugs and other agencies on the pupil . . .866 



543. The nervous mechanism of accommodation 868 



544. The association of the movements of accommodation and the move- 

 ments of the pupil 868 



SECTION IV. 

 IMPERFECTIONS IN THE DIOPTRIC APPARATUS. 



545. Imperfections of accommodation 870 



546. Spherical aberration . .871 



547. Astigmatism 871 



548. Chromatic aberration 873 



549. Entoptic phenomena 874 



SECTION V. 

 ON 'SOME GENERAL FEATURES OF VISUAL SENSATIONS. 



550. The relation of the sensation to the intensity of the stimulus ; 



Weber's law 878 



551. The relation of the sensation to the duration of the stimulus . . 881 



552. Flickering and continuous sensations 883 



553. Sensations produced by various changes in the retina referred to 



some external source of light 883 



554. Localisation of visual sensations 885 



656. The conditions of discrete visual sensations 886 



656. The region of distinct vision. The limits of distinct vision . . .887 



557. Nature of the discreteness of visual sensations ; retinal visual units 889 



