be used if the subject has not a resonant voice.  It has the great disadvantage of being extremely variable.  It is very sensitive to moisture, even when kept as loose as possible, and cannot be depended on to give the same results from day to day.  The records marked Hu., Ha. and G. were usually taken with a glass diaphragm, which has the advantage of being invariable.  As the phonograph records show, glass does not modify the lower tones of the male voice to any extent.

[Illustration:  PSYCHOLOGICAL REVIEW.  MONOGRAPH SUPPLEMENT 17.  PLATE X.
               Opposite p. 436. 
The apparatus is shown arranged for taking parallel records on the smoked glass disc, and on the cylinder of the graphophone.  On the left is shown the microscope with which the records on the glass disc were measured. ]

The speaking-tube used was of woven material, not of rubber, and a pad of felt was kept in the tube near the diaphragm box.  As far as possible more damping was used at the other end of the tube, but this had to depend on the voices of the subjects.

The best check on the performances of a diaphragm is the number per second and character of the vibrations.  The pitch may be calculated from the rotation rate of the disc, which is very constant, as it is driven at a low rate by the well-regulated high-speed motor of the phonograph.  But it is better to place a fork in position to write on the disc and take a parallel record.  All the records were taken with the vowel ‘a’ (sound as in father).  This vowel has a very characteristic signature, which is easily seen, even in a very closely packed curve, and the correctness of this is one of the best guarantees that the fundamental of the tone is actuating the diaphragm (though that does not mean that the diaphragm is actually giving the vibration frequency of that fundamental).

Every record was repeated at least twice, and both records were measured.  In many of the experiments the intensities were fixed by the conditions of the experiment.  There was always the corroborative testimony of the phonograph diaphragm; for the two were not apt to err together.  It was easy to determine if the actual intensity relations were preserved in the phonograph (but it could not be taken for granted).  Each record was reproduced on the phonograph immediately after it had been taken, and both subject and operator listened for anomalies.  In practice it was not hard to get records of the single vowel used (at a small range of pitch which was never more than a third or fourth and was nearly always much less) which represented fairly well the relative intensities.  Beside the checks spoken of above, every record was repeated by a number of subjects, and the comparison of the results of different voices shows uniformity.

The recording of spoken verse is another matter.  It is not difficult to test a diaphragm carefully through a small range, but to be certain of its action at all the pitches and qualities of the speaking voice is impossible.  A stable diaphragm, glass or mica, would have to be used, and careful corrections made for the different vowels.