576 THE SENSES AND SENSORY ORGANS. 



creased in the same ratio with that of the subcorneal image 

 by increasing the effective angular aperture of the corneal 

 lens. 



The actual illumination of the retinal image will then vary 

 inversely as the magnifying power or the square of the linear 

 magnification (;;z-) of the second image as compared with the 

 first, and directly as the intensity of the illumination of the 

 first image, which increases with the surface of the corneal 

 lens, and the angular aperture of the second lens. 



The surface of the corneal lens is generally very large as 

 compared with the surface (a) cut by the axial pencil (1 1 1' /') ; let 

 it be equal to A. Then the illumination of every point of the 

 subcorneal image will be equal A I, and of the retinal image 



to .-, which will evidently be very large in comparison to - 



111 j /I 



distributed over the whole surface (a), since A is usually greater 

 than in-, or, in other words, the waves of light are concentrated 

 by the lens systems. 



In the above the reflection or absorption of light at the 

 refractive surfaces and in the media has been neglected, but 

 this is immaterial to the argument. 



It appears, therefore, that the presence of a corneal lens can 

 only aid vision when an image actually falls upon a recipient 

 structure, and as it can be shown that no such structure exists 

 in the position of Gottsche's image, the inference is that a 

 second refraction must occur beyond the image, and that a 

 second real image is formed, the existence of which has 

 been demonstrated by Exner's photograph. 



To suppose that a retinal image can be produced by the 

 divergent pencils beyond the focal plane of Gottsche's image 

 without a second image being formed is as inconceivable as 

 that a pin-hole camera would form a picture if a small convex 

 lens were added at the pin-hole and the receptive surface were 

 at a distance behind it equal to many times the length of the 

 principal focus of this lens. 



