ZV;.s/Lr\V LV THE ORGAXIC WORLD. 425 



this wonderful organ possesses a power to which no optical instru 

 ment of human construction can show the remotest parallelism, 

 that of adjusting itself to differences of focal distance. Thus, if I 

 close one eye, and hold up my finger between my other eve and 

 the clock at the far end of the room, I cannot see both of them 

 distinctly at the same time, because, as they are at different dis 

 tances from my eye, their pictures on my retina cannot both be 

 distinct. l&amp;gt;ut, without moving either my head or my eye, I can 

 so &quot; locus &quot; my eye on either as to see / / distinctly, the other 

 becoming ha/.y. This we all constantly do without the least 

 knowledge of the mechanism by which it is effected : and all that 

 the most careful and refined investigation has revealed to the 

 1 hysiologist, is that the focal adjustment is made by a change in 

 the curvature of the crystalline lens; its curvature being increased 

 when the rays that fall upon it are more divergent, because pro 

 ceeding from a nearer object ; and being diminished when the 

 rays, proceeding from a more distant object, are less divergent ; 

 so as in each ca-&amp;gt;e to bring them to a focus on the retina. This 

 change of curvature is produced, it is believed, by the action of 

 the ciliary muscle which surrounds the lens ; but how that action 

 is called forth we do not know. Indeed, we are quite unconscious 

 that we are putting it into contraction. I simply determine, I 

 &quot; will look at the clock,&quot; or, &quot; I will look at my finger,&quot; and my 

 eye adjusts itself accordingly. If, on the other hand, I were to 

 look with a telescope, first at a watch-face a few feet off, and then 

 at a church-clock at a distance, I should have to dimmish the 

 distance between the object glass and the eye-piece ; and I cannot 

 conceive of any optical mechanism by which the telescope could 

 be enabled to make this adjustment for itself. That the eye should 

 be provided with such a mechanism, has always seemed to me a 

 most wonderful evidence of intelligent design ; and the importance 

 of this provision in our daily life is so great (as every one knows in 

 whom it is even partially deficient&quot;), as to outweigh beyond all 



* While a person with good ordinary vision has a ranjje of focal adjust 

 ment from sixorcijjht inches (ten inches ln-in^ the (military &quot; reading distance &quot;) 

 to as many miles, that of a &quot; shoi t-M^hu-d &quot; pet son is limited to near objects, 

 and that of an elderly &quot; long-sighted &quot; person to distant ol.jects. A ////&amp;lt;// 

 want of power to adjust the focus of the eyes is seldom met with ; hut some- 

 limes occurs as one of the odd local paralyses often left for a time by an attack 

 ol diphtheria, 



