158 



The Dancing Mouse 



ness of the layer of solution, gives that degree of brightness 

 by which the electric-box was illuminated. 



Tests of the dancer's ability to discriminate green and 

 blue 1 in the transmitted light apparatus were made with four 

 animals. An incandescent lamp marked i6-candle-power 

 was set in each of the light-boxes. These lamps were then 

 so placed that the green and the blue seemed to be of equal 

 brightness to three persons who were asked to compare them 

 carefully. Their candle-meter values in the positions selected 

 were respectively 18 and 64, as appears from the statement of 

 conditions at the top of Table 22. 



TABLE 22 



GREEN-BLUE TESTS 



Brightnesses Equal for Human Eye 



Green 18 candle meters Blue 64 candle meters 



1 Hereafter the light transmitted by the blue-violet filter will be referred 

 to for convenience as blue. 



2 A single preference series of twenty tests. 



