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THE PHONOGRAPHIC METHOD 37
Total variation during Series III .9 vibr. = 6c. After the series was completed I tried the effect of bearing down with the hand on the regulator screw without turning it. The result was a relaxation in the rapidity of the beats, which became faster again when the pressure was relaxed. Since this pressure on the screw produced minimally the same effect as would follow in greater degree from turning down the screw, this slowing of the beats proved again that the phonograph note was above that of the fork.
The result here was almost exactly the same as before, the note being if anything a little more constant. The initial pitches differed by J, the final by
vibration. As in I and II, the change in the beats is a gradual quickening from beginning to end of the cylinder.
These three tests indicated that, while under favorable circumstances a constant note would at the same spot in the cylinder be given in several immediately successive reproductions at the same pitch to within an almost imperceptible fraction of a tone (in general not more than, the instrument was subject
to a constant aberration, a sharping of pitch, as the reproduction went on by a much larger though still very minute interval, not more than aboutof a tone.
During all of the tests thus far described, the motor of the phonograph had been supplied with electricity from a single storage battery (Battery 1) of 150 amperes. On taking up the experiments again after an absence of ten days, during which time the phonograph and the battery had stood idle, I obtained from Cylinder B very different and much inferior results to those just reported. Since it was now two weeks since the battery had been charged, I concluded