THE REFRACTING TELESCOPE. 



179 



Diagram 4. 



a shock, the sensation of a point of light is produced. As shown in 

 the diagram, just one rod is agitated by each set of waves, so that the 

 eye sees in this case two distinct points of light, the brilliancy of 

 each depending upon the intensity of the agitation. A third vibrating 

 molecule in another star would be seen by the eye in the same way, 

 and so on indefinitely. 



As the color of light depends merely on the wave-length, we can 

 now understand how the eye sees the constellations in their true con- 

 figurations and colors ; and, as reflected light has the same effect on 

 the eye as that coming directly from self-luminous points, it is plain 

 that the eye must see the form and color of all luminous objects, each 

 individual point of each object forming its own focus on one of these 

 sensitive rods of the retina. 



Can any mechanism be more simple and beautiful than that of vis- 

 ion ? The more it is studied the more admirable it seems, and we are in a 

 still better position to appreciate the elegance of the mechanism which 

 enables the lens of the eye to form a pei'fect image of distant objects 

 upon the sensitive retina, when we take into consideration the fact 

 that, were the waves of light not so excessively minute, distinct vision 

 would be utterly impossible. 



It is only because the light-waves are so much smaller than the 

 aperture of any lens, such as the lens of the eye, that they run to a 

 focal point, instead of spreading out in all directions, as do the waves 

 of sound which enable us to hear round a corner. The effect of de- 

 creasing the aperture of the lens of the eye to a size comparable with 

 that of the light-waves (which would in effect be the same as increas- 

 ing the length of the light-waves to a size comparable with that of the 

 eye) can easily be shov/n thus : 



