STUDYING CONTROLLED WORD ASSOCIATIONS 373 



keep it down until after the response word is spoken, and then 

 read the reaction time directly. 



The superiority of this chronoscope lies in the fact that it has 

 no significant error, is extremely simple in operation, and runs 

 continuously and noiselessly. It can run neither slow nor fast 

 by the smallest fraction of time, else the motor gets out of step with 

 the fork and stops. The only possible elements of error lie in 

 (a) a possible change of vibration rate of the fork due to temper- 

 ature changes, which can be obviated by enclosing it in a box with 

 a thermostat, but which for this work is a negligible factor, (b) a 

 possible error in the divisions of the dial, and (c) in a possible 

 difference in reluctance of the disc between the magnets, in pass- 

 ing in opposite directions, due to a possible difference in the 

 strength of the two fields. This last was found to be negligible 

 in the chronoscope used. 



The chronoscope will run continuously if care is taken to keep 

 the fork contact properly adjusted. By experimenting, platinum 

 wire was found impracticable for this; it burns up too quickly and 

 has not enough spring to give the optimum length of period of 

 contact for the motor to " catch." A gold alloy wire was tried, 

 the wire used in dental work, and found extremely satisfactory. 

 The gauge of the wire and its length are important, but these two 

 factors must be determined empirically. As the wire burns back, 

 the contact must be readjusted to keep the optimum period of 

 contact for the motor. Only when this fails does the motor stop. 

 Adjusting and cleaning the contact about twice a day when it is 

 being used continuously all day has usually been found sufficient. 

 The motor was run on the following voltage and amperage: 



Voltage: 10.0 volts, closed fork contract, but not vibrating. 



Voltage: 30.0 volts, broken fork contact. 



Voltage: 25 A volts, fork running on optimum contact for motor; 

 motor dead. 



Voltage: 25 .4 volts, fork running, motor running. 



Amperage: 1.3 amperes, closed fork contact, but not vibrating. 



Amperage: 0.3 amperes, fork running on optimum contact for motor; 

 motor dead. 



Amperage: 0.3 amperes, fork running, motor running. 



