ifferent adjustments of the tongue, palate, and larynx are concerned in
the production of the various registers. This _Memoire_ opened up a new
line of observation, in which Garcia continued to take the lead. But the
extending of the scope of inquiry concerning the registers did not
result in any unanimity of opinion on the part of the vocal
investigators of that time.

For a few years following the invention of the laryngoscope (1855),
vocal theorists ceased their disputes about the registers, and awaited
the definite results of this new mode of observation. When this potent
little instrument was put within the reach of every investigator, it was
believed that the mystery surrounding the registers was about to be
dispelled.

One important consequence of the invention of the laryngoscope was the
turning of attention away from the sensations of vibration in the chest
and head. Each register was ascribed to a distinct mode of operation of
the vocal cords, and for several years the terms "chest voice" and "head
voice" were held to be scientifically unsound. But with the publication
of Helmholtz's _Die Lehre von den Tonempfindungen_ in 1863, the
sensations of vibration again received attention. These sensations were
then made the basis of a theory of vocal resonance, which has since been
adopted by the great majority of vocal scientists.

Until the publication of Helmholtz's work vocal theorists had known
practically nothing of acoustics. The fact that the tones produced by
the vocal cords are increased in power and modified in quality by the
resonance of the air in the mouth-pharynx cavity came as a distinct
revelation to the theoretical students of the voice. Helmholtz confined
his experiments and demonstrations to the mouth-pharynx cavity, and
investigated in particular the influence of this cavity in producing the
various vowel and consonant sounds. But vocal theorists at once extended
the idea of air resonance, and connected it with the well-known
sensations of vibration in the chest and head. It was assumed that these
sensations are caused by vibrations of the air in the chest and nasal
cavities.

This assumption has been accepted without question by the great majority
of vocal scientists. Both the chest voice and the head voice are now
believed to owe their distinctive qualities to the reinforcing
vibrations of the air in the chest and nasal cavities respectively. The
mere fact that these vibrations can be felt i