468 H. M. JOHNSON 



to inhibit reaction in such cases. If reaction is not inhibited, 

 the fact is recorded; but false reactions are not included in the 

 averaged results. 



A Johns Hopkins chronoscope, 9 operated in an adjacent room, 

 records the time elapsing between the opening of the circuit 

 through LI or L 2 , and the subject's reaction. A part of the 

 latent period of the lamp is thus added to the subject's reaction- 

 time. Correction for this constant was not made in the results 

 as presented. From data furnished by my colleague in physics, 

 Dr. A. G. Worthing, it appears that with the lamps used, and 

 under the conditions of the experiment, the added brightness 

 would be reduced to 0.5 per cent of the brightness of the test- 

 field and thus become completely effective, in 0.022 second after 

 the current is interrupted; but it would be reduced to 90 per cent 

 of its own original value, and begin to be effective, in 0.0006 

 second. I am uncertain what correction should be applied. 

 It is clear, however, that the correction is constant and relatively 

 small with respect to the variable to which it belongs. 



The method of presenting the stimuli is simple, and is readily 

 ascertained from inspection of the wiring diagram in figure 2. 

 The wiring of the pendulum magnet, and of the warning buzzer 

 and the buzzer with which the subject, when necessary, signalled 

 the experimenter, are not shown, but are independent of the 

 rest of the system. 



The chosen supplementary lamp LI or Z/ 2 is cut out, and the 

 chronoscope started by the pendulum breaking the lamp circuit 

 and the circuit through the stationary magnet of the chronoscope 

 at PSi. The lamp circuit is broken a second time at P& so 

 that the lamp is not re-lighted when P& is closed an instant 

 later to restore the circuit through CCi before the subject reacts. 

 On its return swing, the pendulum closes PS Z and P$i in the 

 order given, but does not re-open PS 3 , which is opened by hand 

 after the chronoscope is read. 



Inspection of figure 2 will make it apparent that if the switch 

 ESi is open and if the bank of double-throw switches ES 2 , ES*, 



9 Dunlap, Knight: The Johns Hopkins Chronoscope. Journ. Exper. Psycho!, 

 ii, 1917; pp. 249-252. 



