Tke Sense of Sight : Brightness Vision 119 

 c, 



FIGURE 17. Weber's law apparatus for testing brightness discrimination. 

 Lower part, discrimination box similar to that of Figure 14. Upper part, rotatory 

 light-box, pivoted at A, and divided into two compartments by a partition P in 

 the middle. L, L, incandescent lamps movable in slits, 5, B, in which a narrow 

 strip of leatherette, C, serves to prevent the escape of light. S, scale. 



