Although almost entirely ignorant of vocal mechanics in the scientific sense, the old masters were eager students of the voice. They carefully noted the characteristic sound of each tone of the voice, and worked out what they believed to be a comprehensive theory of tone-production. One of their observations was that in every voice the low notes have a somewhat different quality from the high notes. To distinguish these two qualities of tone the old masters adopted the word used for a similar purpose by the organ builders,--_register_. Further, they noted the sensation of vibration in the chest caused by singing low notes, and concluded that these notes are actually produced in the chest. To the lower notes of the voice they therefore gave the name "chest register." As Tosi explains it, "_Voce di Petto_ is a full voice, which comes from the breast by strength." For a precisely similar reason, viz., the sensation of vibration in the head felt in singing the higher notes, this portion of the voice was called by the old masters the "head register." When the study of vocal mechanics along scientific lines was undertaken, in the early decades of the nineteenth century, attention was at first paid almost exclusively to the subject of registers. The questions then most discussed were the number of registers, the number of notes which each should include, and the precise point of production of each register in the chest, throat, and head. Garcia's _Memoire_, dealing with the registers, was noticed in the preceding chapter. He showed that different 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.