BINOCULAR VISION 



875 



of the air. Inasmuch as the latter is not entirely transparent, distant 

 objects cannot be seen so clearly as near objects. In many cases, 

 this obscuration of the luminous rays of an object frequently prompts 

 us to form an erroneous judgment. Thus, an object dimmed by a 

 mist "looms large," because we associate indistinct vision with 

 distance and hence, the sudden relatively large visual image produced 

 by this near object, leads us to overestimate its actual size. 

 Concurrently, the size of an object seen in a clear atmosphere, is 



L a 



FIG. 473. RIGHT- AND LEFT-EYED IMAGES OF TRUNCATED PYRAMID. MAY BE COM- 

 BINED TO PRODUCE SOLID IMAGE BY RELAXING THE ACCOMMODATION THAT is, GAZING TO 

 A DISTANCE THROUGH THE BOOK. 



generally under-valued for the reason that distinct vision is 

 associated with near objects. 



The judgments regarding the depth or solidity of objects are formed 

 in a similar way, i.e., they are based upon several factors, namely: 



(a) The difference, in the images formed in the two eyes. Since the eyes are 

 separated from one another by a certain distance, the right eye sees more of its 

 right side and the left eye, more of its left side. This difference in the projection 



FIG. 474. STEREOSCOPIC PICTURE OF AN OCTAHEDRAL CRYSTAL. MAY BE COMBINED 

 STEREOSCOPICALLY BY RELAXING THE ACCOMMODATION BY THE METHOD OF HETERONYMOUS 

 DIPLOPIA. HOLD THE OBJECT AT A DISTANCE OF A FOOT OR MORE AND GAZE BEYOND. 



leads to a corresponding difference in the associations. It becomes more pro- 

 nounced, the nearer the object. 



(6) Mathematical perspective. Objects appear in relief and we have learned 

 to interpret perspective correctly. 



(c) Lights and shadows aid our judgment according to their distribution 

 through the visual field. 



(d) The muscle-sense plays a part in accommodation as well as in the con- 

 vergence of the visual axes. 



(e) Condition of the atmosphere. More distant objects are not so clear as 

 near objects. 



