GENERAL CONDITIONS OF BRAIN- ACTIVITY. 87 



line a * time-line ' of which each undulation or link stands 

 for a certain fraction of a second, and against which the 

 break in the reaction-line can be measured. Compare 

 Fig. 21, where the line is broken by the signal at the first 

 arrow, and continued again bj the reaction at the second. 

 Ludwig's Kymograph, Marey's Chronograph are good ex- 

 amples of this type of instrument. 



Another type of instrument is represented by the stop- 

 watch, of which the most perfect form is Hipp's Chrono- 

 scope. The hand on the dial measures intervals as short 

 as yoVo ^^ ^ second. The signal (by an appropriate electric 



Pig. 2v?.— Bowditch's Reaction-timer. F. tuning-fork carrying a little plate wliich 

 holds the paper on which the electric pen Jl/ makes the tracing:, and sliding n 

 grooves on the base-board. P, a plug which spreads the prongs of the fork apart 

 when it is pushed forward to Irs extreme limit, and leleases them when it is drawn 

 back to a certain point. The fork then vibrates, and, its backward movement con- 

 tinuing, an imdulating line is drawn on the smoked paper by the pen. At yis a 

 tongue fixed to the carriage of the fork, and at K an electric key which the tongtie 

 opens and with which the electric pen is connected. At tlie instant of opening, the 

 Den changes its place and the undulating line is drawn at a different level on the 

 paper. The opening can be made to serve as a signal to the reader in a variety 

 of ways, and his reaction can be made to close the pen again, when the line re- 

 turns to its first level. The reaction time = the number of undulations traced at 

 the second level. 



connection) starts it ; the reaction stops it ; and by reading 

 off its initial and terminal positions we have immediately 

 and Avith no farther trouble the time we seek. A still 

 simpler instrument, though one not very satisfactory in its 

 working, is the * psychodometer ' of Exner & Obersteiner, 

 of which I picture a modification devised by my colleague 

 Professor H. P. Bowditch, which works very well. 



The manner in which the signal and reaction are con- 

 nected with the chronographic apparatus varies indefinitely 



