1 1 8 The Dancing Mouse 



as importantly to the solution of our first problem as to 

 that of the second, for which it was especially planned. 



For the Weber's law experiment a box similar to that used 

 in the previous brightness discrimination experiments (Figure 

 14) was so arranged that its two electric-boxes could be 

 illuminated independently by the light from incandescent 

 lamps directly above them. The arrangements of the light- 

 box and the lamps, as well as their relations to the other im- 

 portant parts of the apparatus, are shown in Figure 17. The 

 light-box consisted of two compartments, of which one may 

 be considered as the upward extension of the left electric- 

 box and the other of the right electric-box. The light-box 

 was pivoted at A and could be turned through an angle of 

 1 80 by the experimenter. Thus, by the turning of the light- 

 box, the lamp which in the case of one test illuminated the 

 left electric-box could be brought into such a position that in 

 the case of the next test it illuminated the right electric-box. 

 The practical convenience of this will be appreciated when 

 the number of times that the brightnesses of the two boxes 

 had to be reversed is considered. The light-box was left open 

 at the top for ventilation and the prevention of any consider- 

 able increase in the temperature of the experiment box. In 

 one side of each of the compartments of the light-box a slit 

 (B, B of the figure) was cut out for an incandescent lamp 

 holder. A strip of leatherette, fitted closely into inch grooves 

 at the edges of the slit, prevented light from escaping through 

 these openings in the sides of the light-box. By moving the 

 strips of leatherette, one of which appears in the figure, C, the 

 lamps could be changed in position with reference to the bottom 

 of the electric-box. A scale, 5, at the edge of each slit enabled 

 the experimenter to determine the distance of the lamp from 

 the floor of the electric-box. The front of the light-box was 

 closed, instead of being open as it appears in the figure. 



