248 MEMORIES OF MY LIFE 



their ears with their paws, just as the persons of whom 

 I have spoken often did with their hands. 



It was difficult to find a simple machine that 

 would register the length of Reaction Time that is, 

 the interval between a Stimulus and the Response to 

 it, say between a sharp sound and the pressure of a 

 responding finger on a key. I first used one of 

 Exner's earlier instruments, but it took too much 

 time, so I subsequently made one with a pendulum. 

 The tap that released the pendulum from a raised 

 position made the required sound, otherwise it made 

 a quiet sight-signal, whichever was wished, and the 

 responding finger caused an elastic thread parallel to 

 the pendulum and swinging with it to be clutched 

 and held fast, in front of a scale, graduated to T ^oths 

 of a second. This acted well ; there was no jar from 

 seizing the elastic thread, and the adjustments gave 

 no trouble. 



For testing the Muscular Sense, I used cartridges 

 packed evenly with cotton wool and with shot, so as 

 to be exactly alike on the outsides but of different 

 weights. The weights ran in a regular geometric 

 series, and were broken up into sets of three. Each 

 set lay in a grooved square of wood, in any order ; 

 the test was to arrange them by the sense of their 

 heaviness, in their proper order, as shown by the 

 inscriptions at one end of each. This method acted 

 quickly, because it was easy to judge by the some- 

 times hesitating, sometimes decided manner in which 

 a particular set was handled, whether or no the 

 differences were clearly perceived, and to substitute 

 others in turn more appropriate to the acuteness of 

 sense of the person tested. 



