The Cause of Life and Motion 39 



and therefore if the optic nerve should be dis- 

 troyed there would be no vision, for the recipro- 

 cal circuit would thus be broken. 



When we look at the two pictures in a stereoscope, 

 we have a perfect realization of form, but although the 

 pictures may be at the proper focal distance, the scene 

 appears in miniature, and in case they should repre- 

 sent a group of human beings t and should even be 

 magnified so that they would subtend a much greater 

 angle than the natural scene; the figures, nevertheless, 

 would appear like Liliputians. Perhaps the scientist 

 would say that this was merely imagination. He might 

 also say, that our estimate of from ten to twelve inches 

 for the sun's apparent diameter, was imagination, 

 since it forms an image on the retina much less in size 

 than an ordinary pin's head. The scientist will event- 

 ually find, that there is method in this much abused 

 faculty of imagination. In stereoscopic pictures we 

 have all the elements for producing the exact image, 

 excepting the color, of a scene on the retina, as it 

 would be produced naturally. Nevertheless, we do 

 not by any means, get the natural ejfect of size. But 

 let the stereoscopic pictures be enlarged to the full 

 natural size and placed at the proper distance, and 

 then if a few mirrors should be adjusted to bring ij^e 

 visual rays of the spectator's eyes, respectively, within 

 the center of each picture, the effect of size would be 

 found to be nearly natural, and yet the image on the 

 retina would be less in size than before. 



The Derivation of Action. 



In all the preceeding manifestations, we have 

 evidence which points with unerring certainty, 



