40 HARRY MILES JOHxXSON 



rod, which shows this distance accurately. Then if the amount 

 of current passing through the magnet of the stimulus-fork be 

 known and the distance of the resonator from the fork be also 

 known, it will be possible to duplicate these conditions and 

 convert these readings into absolute units of intensity in case 

 a means of measuring it satisfactorily should ever be perfected. 



If a wooden resonance case is used instead of the Konig or 

 Helmholtz resonator, results are not so satisfactory. Intensity 

 can indeed be \-aried by varying the amount of current passing 

 through the magnet of the stimulus-fork, but if the current used 

 be strong, overtones become quite prominent. Besides the 

 fundamental tone of the fork, there are also present a high 

 anharmonic partial and an undertone of the pitch of the primary 

 fork. The latter is caused by periodic increases in amplitude 

 of vibration of the secondary fork, which synchronize with the 

 vibration of the primary fork, due to the impulse of the current 

 made and broken by the primary. This undertone, however, 

 seems to be mediated by the wood of the table and of the reso- 

 nance case. If the latter be removed and a Konig resonator 

 substituted for it, and if the stand on which the stimulus-fork 

 is mounted be padded heavily with cotton Imtting, then this 

 undertone is not detectible b}^ the human subject, even with 

 the aid of a resonator. Under the same conditions the high 

 partial cannot be heard by the best human observers at a dis- 

 tance exceeding two feet, so it probably does not work much 

 disturbance. No OA'ertones can be detected by use of the ordi- 

 nary resonators. The maximum intensity of the fundamental 

 is very great. 



By this means may he obtained a tone \\hich is practically 

 pure, of widely variable if not measurable intensity, incapable 

 of being localized by the human subject at least, and free from 

 accessory noise. 



Through the use cf such a system and the stimulus-cage 

 described above, I believe that it is possible to meet all the 

 conditions of reliable tests on pitch-discrimination in animals 

 which I have enumerated above : the elimination of unconscious 

 helps; the elimination of the "delayed reaction" factor; the 

 use of a decisive criterion of discrimination; and the control- 

 abilitv ( f the stimulus. 



