128 The Dancing Mouse 



For the purpose of settling this point I made tests for each 

 of the three standards with a difference of only one fifteenth. 

 In no instance. did I obtain the least evidence of ability to 

 discriminate. These final tests, in addition to establishing 

 the fact that the limit of discrimination for No. 51, after she 

 had been subjected to about two thousand tests, lay between 

 one tenth and one fifteenth, proved to my satisfaction, when 

 taken in connection with the results already discussed, that 

 Weber's law does hold for the brightness vision of the dancer. 



In concluding this discussion of the Weber's law experi- 

 ment I wish to call attention to the chief facts which have 

 been revealed, and to make a critical comment. In my 

 opinion it is extremely important that the student of animal 

 behavior should note the fact that the dancer with which 

 I worked week after week in the Weber's law investigation 

 gradually improved in her ability to discriminate on the 

 basis of brightness differences until she was able to distin- 

 guish from one another two boxes whose difference in illu- 

 mination was less than one tenth * that of the brighter 

 box. At the beginning of the experiments a difference of one 

 half did not enable her to choose as certainly as did a differ- 

 ence of one tenth after she had chosen several hundred times- 

 Evidently we are prone to underestimate the educability of 

 our animal subjects. 



The reason that the experiments were carried out with 

 only one mouse must now be apparent. It was a matter of 

 time. The reader must not suppose that my study of this 

 subject is completed. It is merely well begun, and I report it 

 here in its unfinished state for the sake of the value of the 

 method which I have worked out, rather than for the purpose of 

 presenting the definite results which I obtained with No. 51. 



1 Under the conditions of the experiment I was unable to distinguish the 

 electric -boxes when they differed by less than one twentieth. 



