534 THE HUMAN BODY. 



142 to the ordinary size of a stereoscopic slide, and placing 

 them in the instrument. A solid pyramid standing out 

 into space will be distinctly perceived; if the pictures be 

 reversed the pyramid appears hollow. The pictures must 

 not be too different, or their combination to give the idea 

 of a single solid body will not take place. Many persons, 

 indeed, fail entirely to get the illusion with ordinary stereo- 

 scopic slides. The phenomena of stereoscopic vision mili- 

 tate strongly against the view that there are any pre- 

 arranged corresponding points in the two retinas. 



The Perception of Shine. When we look at a rippled 

 lake in the moonlight, we get the perception of a "shiny" 

 or brilliant surface. The moonlight is reflected from the 

 waves to the eyes in a number of bright points: these are 

 not exactly the same for both eyes, since the lines of light- 

 reflection from the surface of the water to each are 

 different. The perception of brilliancy seems largely to 

 depend on this slight non-agreement of the light and dark 

 points on the two retinas. A rapid change of luminous 

 points, to and fro between neighboring points on one 

 retina, seems also to produce it 



