SYSTEMATIC SYNTHESIS OF TISSUES INTO ORGANS. 299 



787. Remark. A larger office HAS FREQUENTLY BEEN ATTRIBUTED 

 TO THE EYE than it is possible or desirable for it to perform, and when an 

 attempt has been made to explain what of course was unexplainable, it 

 has been found that the explanation itself must be explained. The ele- 

 ments of knowledge gained through the eye are few, very simple, yet com- 

 plete, and quite sufficient. The mind should not be embarrassed, when 

 studying the eye, with previous theories and dogmas, such, for example, 

 as that there are images in the eye; that they are inverted, etc. (PI. 8.) 



788. THE PERFECTION OF SIGHT DEPENDS UPON 

 having a healthy nervous structure, and upon having 

 the light from each visual object brought with the ut- 

 most exactness to its corresponding visual point in the 

 eye. 



789. Experiment. IF TWO OR MORE LIGHTS ARE PLACED IN A 

 STRAIGHT LINE before the lens, their foci will not be found in a straight, 

 but in a curved, line, and the degree of curvature will depend upon the 

 distance of the lights. 



790. Inf. THE RETINA MUST HAVE an exact curvature correspond- 

 ing to tjie foci naturally produced, and the curvature must be changea- 

 ble to suit objects at different distances. 



791. Experiment. IF A LIGHT is HELD BEFORE A CONVEX LENS, AND 

 ITS FOCUS OBSERVED, it will be found to vary in its distance from the lens, 

 either by the motion of the light toward or from the lens, or by the 

 movement of the lens toward or from the light. If the lens be ex- 

 changed for one more or less convex, the distance of the focus will also 

 be correspondingly changed. 



792. Experiment. But IF THE LENS is MOVED IN THE SAME RATIO AS 

 THE LIGHT, the focus will be at the same point ; or if the screen or object 

 on which the focus is received is moved correspondingly with the light, 

 the focus will of course fall upon it ; or if both the screen and lens be 

 moved according to the needed adjustment, the combined effect will pre- 

 serve the focus at the same point on the screen. 



793. LIGHT FROM DISTANT AND FROM NEAR OBJECTS 

 cannot have its focus at the same point of the retina in 

 the same eye without being changed in some respects. 



794. THE MUSCLES OF THE CILIARY PROCESSES are 

 thought to be the means of regulating the position of 

 the lens and the conditions of the humors in such a 



7S7. What ? 788. what? 789. What ? 790. what? 791. What ? 

 792. What ? 793. What said of ? 794 What is the use of ? 



