176 UNIVERSITY OF COLORADO STUDIES 



Wheatstone 1 constructed the first stereoscope which superposes two 

 similar images by means of mirrors (see Fig. 5), and produces the illusion 

 of depth. This reflecting form of stereoscope is known as " Wheatstone's 

 Stereoscope." In 1849 Sir David Brewster invented the refracting 

 stereoscope (Fig. 9). 



The first real experimenter along the line of visual interpretation was 

 Hueck 3 in 1838, and by him was established the fact that convergence 

 influences our judgment of the position and distance of the object 

 looked at. Meyer 3 between 1848 and 1852 showed a very interesting 

 experiment with the Wheatstone stereoscope. He found that if two 

 figures were inserted in the slides (Fig. 5) at A and B, thus combining 

 them for the observer into a single image, this image appeared to approach 

 or recede in the direction of depth according as the figures in the slides 

 were moved back and forth. By drawings indicating the paths of the 

 reflected rays he showed that the change of apparent distance was, 

 throughout the series, consistent with the changes of convergence of the 

 visual axes of the eyes. 



Two views arose with reference to fundamental factors of vision. 

 These were held by the empiricists and nativists. Nearly all those who 

 experimented with the stereoscope were of the former class, and Berkeley 

 is one of the best representatives of this school. The great representa- 

 tives of the other school were Johannes Miiller, 4 Lotze, 5 and Hering. 6 

 Miiller held that the capacity to see space was innate, but that sensations 

 of movement by association become important secondary factors in 

 adult perception of space. Almost everyone is familiar with the Lotzian 

 theory of Local Signs. When an object comes into the field of vision, 

 the eyes reflexly turn so as to bring its image upon the two foveae. 

 The movement accompanying the transference of the image from any 

 peripheral point to the fovea differs in magnitude and direction 



1 Wheatstone, "Contributions to the Physiology of Vision," Philosophical Transactions (1838). 

 ' A. Hueck, Die Achsendrehung des Anges (1838). 



3 Hermann Meyer, "Uber die Schatzung der Grosse und Entfernung." Poggcndorfj's Annalen der 

 Physik und Chemie (1852). 



* Muller, Vergleichende physiologie des Gesichtsinnes (1826). 



s Lotze, Medicinische Psychologic (1852). 



6 Hering, Die Lehre vom binocularen Sehen (1868). 



