rouse: the visum, perception of distance. 



Fig. 1. 



In the figure above, E represents a light-brown paste-board box, 

 suspended with an invisible wire (D ) to a larger wire (AB), by 

 means of a smooth ring (Cj capable of sliding back and forth. 

 Four such cubical boxes were employed, their edges measuring, 

 respectively, 2, 3, 4, and 5 centimeters. The larger wire (AB), 

 supporting them, was tightly drawn in a horizontal position over- 

 head and extended the entire length of the 52 foot room. Two tin 

 tubes ( F), well smoked inside, were so fixed at one end of the room 

 that they were directl}- below the horizontal wire (AB), parallel 

 with it, and in the same horizontal plane with the boxes when sus- 

 pended successively. A curtain of plain dark material ( H) was 

 placed at the further end of the room, just below and at right angles 

 to the wire drawn above. 



Two persons were required (besides the subject) to perform the 

 experiment, one to move the boxes back and forth (with a long 

 stick or pointer) to correspond with divisions of a chalk line drawn 

 upon the floor directly below the horizontal wire (AB), and another 

 to give the subject views of the boxes when placed at proper posi- 

 tions, not permitting him to see them moved, or to know when one 

 box was exchanged for another, and to keep account of estimations 

 made, thus leaving the subject free to judge the distance of the 

 objects at different positions. Views at the proper time were given 

 b}^ uncovering the farther ends of the tubes, a large piece of paste- 

 board (M), perforated with holes through which the nearer ends of 

 the tubes passed, cutting off all view in front of the subject except 

 through the tubes. 



In the experiment ten young men from the higher classes of the 

 university were used as subjects, each sitting at the opposite end 

 of the. room from the curtain, and judging the distance of each of 

 the four boxes, when placed in a definite series of positions. 

 When judging distance at the first of the experiment the subject 

 looked through the tubes and saw nothing but the suspended boxes 



