126 The Dancing Mouse 



After finishing the experiments with the 80 standard on 

 May 27 (see table) I decided, in spite of the evidence against 

 Weber's law, to make tests with 5 as the standard, for it 

 seemed not impossible that the lights were too bright for the 

 dancer to discriminate readily. I even suspected that I 

 might have been working outside of the brightness limits 

 in which Weber's law holds, if it holds at all. The tests 

 soon showed that a difference of one tenth made dis- 

 crimination possible in the case of this standard. If the 

 reader will examine the data of the table, he will note that a 

 difference of .20 gave 14 per cent of mistakes; a difference 

 of .03, 48 per cent. Evidently the former difference is above 

 the threshold, the latter below it. But what of the interpreta- 

 tion of the results in terms of Weber's law? The difference 

 instead of being one half or one fifth, as it was in the cases of 

 the 20 and 80 standards respectively, has now become one 

 tenth. Another surprise and another contradiction ! 



Had these three differences either increased or decreased 

 regularly with the value of the standard I should have sus- 

 pected that they indicated a principle or relationship which is 

 different from but no less interesting than that which Weber's 

 law expresses. But instead of reading 5 standard, difference 

 one tenth; 20 standard, difference one fifth; 80 standard, 

 difference one half: or 5 standard, difference one half; 20 

 standard, difference one fifth; 80 standard, difference one 

 tenth: they read 5 standard , difference one tenth; 20 stand- 

 ard, difference one half; 80 standard, difference one fifth. 

 What does this mean ? I could think of no other explanation 

 than that of the influence of training. It seemed not impos- 

 sible, although not probable, that the mouse had been im- 

 proving in ability to discriminate day by day. It is true that 

 this in itself would be quite as interesting a fact as any 

 which the experiment might reveal. 



