38 HARRY MILES JOHNSON 



is kept covered with alcohol, and a secondary circuit through 

 a condenser is made by connecting at pole a and the mercury 

 cup c. This is to eliminate the noise of sparking. 



In the experiment-room, on a table, T, about six feet from 

 the end of alley B of the stimulus-cage shown in Fig i, are 

 placed the stimulus-forks. A diagram of one is show^n with its 

 mounting in Fig. 3. The ones mounted for this work are c-256 

 d.v., e-320 d. v., g-384 d.v. and c-512 d.v. As will be seen these 

 vibration-rates are all simple multiples of that of the primary 

 fork. The stimulus-forks are not provided with contacts but 

 are mounted with magnets between the prongs. The current 

 through these magnets is made and broken at each complete 

 vibration of the primary fork, and the impulse thus given is 

 sufficient to actuate the stimulus forks. The wiring is as fol- 





J 



'^'^'•^'''■ '-r--— ^^ 



B Aq 



rip 



Figure 2 — A, B, binding posts; C, insulated mercury cup; P, P', platinum con- 

 tacts; M, magnet. 



lows ; From the positive pole of a four volt six amperes storage 

 cell to contact a on the mounting of the pvimavy fork, through 

 the fork and platinum contact p' to a second mercury cup not 

 shown in the cut of the primary fork, but which is separated 

 and insulated from mercury cup c by hard rubber mounting; 

 thence to a rheostat, through the magnet coil between the 

 prongs of the stimulus-fork, to a double -throw switch at the 

 table at the experimenter's station ; thence to the negative 

 pole of the storage cell. The primary fork is kept going through- 

 out the daily series; and the experimenter has only to turn 

 the double-throw switch to cause either of the two stimulus- 

 tones to sound. 



Above the stimulus-fork shown in Fig. 3 will be noticed a 

 Konig resonator. This mediates only the pure tone of the 

 stimulus-fork. It is kept in place by a sleeve which is fastened 

 to the upright rod on the fork's stand. A tone of maximum 

 intensity is obtained when the resonator opening is about i mm 

 from the ends of the prongs of the fork. The intensity can be 



