Fig. 8. THE THAUMATROPE. 



THE EYE. 



CHAPTEE II. 



42. Power of accommodation of the eye. 43, 44. Apparent brightness of 

 luminous objects. 45-47. Intensity of brightness. 48-57. The 

 image must continue a sufficient time upon the retina to enable that 

 membrane to produce a perception of it Various illustrations of this. 

 58. Conditions which determine apparent motion. 59. How 

 affected by distance. 60. Example. 61. When imperceptible. 

 62. Motion of the firmament. 63. Objects in rapid motion invisible. 

 64-66. Duration of the impression on the retina. 67. Optical toys. 

 68, 69. Coincidence of^ the optical and geometrical centres of the 

 eye. 70. Ocular spectra and accidental colours. 71. Why visible 

 objects do not appear inverted. 72. The seat of vision. 73-75. The 

 optic nerve insensible to light. 



42. THE eye possesses a certain limited power of accommodating 

 itself to various degrees of illumination. Circumstances which 

 are familiar to every one render the exercise of this power 

 evident. 



If a person, after remaining a certain time in a dark room, 

 pass suddenly into another room strongly illuminated, the eye 

 suffers instantly a degree of inconvenience, and even pain, which 



LARDNER'S MUSEUM OF SCIENCE. F 65 



No. 59. 



