RECORDING AND PHOTOGRAPHING SOUND WAVES
ment ; a stylus attached to one prong of the fork marks a sim¬
ple wave line by the side of the trace from the membrane.
Phonautograph records obtained by Koenig are shown in
Fig. 56, the lower one of each pair of traces is that of the
sound being studied, combinations of organ pipes in this
instance, while the upper trace of each pair is from the
tuning fork, enabling the determination of the frequencies
of the recorded tones. These records are not only small
in size, but the essential characteristics are distorted or
obliterated by friction and by the momentum of the stylus.
The Manometric Flame
In 1862 Koenig devised the manometric capsule in which
the flame of a burning gas jet vibrates in response to the
variations in pressure in a sound wave.34 The capsule c,
Fig. 57, is divided into two compartments by a partition