RATE OF LEARNING IN THE WHITE RAT 



TIMING APPARATUS 

 FIG. 2 



fastened to the shaft of the kymograph, but is carried along by 

 friction on the large revolving disc. If the circuit is closed and 

 the electro-magnet pulls the lever C into place, the arm A is held 

 in the position shown in the drawing. The strength of the 

 magnet is great enough to overcome the friction on the revolving 

 disc. 



By pressing the contact key the circuit of the electro-magnet 

 is broken, and is closed on the electric buzzer. This presssure 

 not only gives the sound stimulus, but it also releases lever C, 

 allowing arm A to be carried along with the revolving disc and 

 to pass over contact B, which closes the circuit through the in- 

 duction coil and the system of wires on the floor of the box. 

 When the contact key is released the current again flows through 

 the electro-magnet, attracting lever C, which keeps the arm A 

 from moving when it again reaches that point. Thus the ap- 

 paratus automatically completes the process, and after 15 seconds 

 it stands ready for a repetition at the will of the experimenter. 

 The friction contacts at D and B are so constructed that the 

 current is broken at the end of one-half second. Each stimulus 

 is, therefore, given for this period of time. By this apparatus 

 it is possible very accurately to present two stimuli in a certain 

 definite temporal relation to each other. 



With certain groups of animals light was used as one of the 

 two terms to be associated. The new apparatus added for pre- 



