The acoustic effect is due to the resonances generated by hollow spaces of the resonator, and Dr. Aikin, in his work on “The Voice,” points out that we can study the resonances yielded by these hollow spaces by whispering the vocal sounds; but it is necessary to put the resonator under favourable conditions for the most efficient production.  When a vowel sound is whispered the glottis is open (vide fig. 10) and the vocal cords are not thrown into vibration; yet each vowel sound is associated with a distinct musical note, and we can produce a whole octave by alteration of the resonator in whispering the vowel sounds.  In order to do this efficiently it is necessary to use the bellows and the resonator to the best advantage; therefore, after taking a deep inspiration in the manner previously described, the air is expelled through the open glottis into the resonating cavity, which (as fig. 13 shows) is placed under different conditions according to the particular vowel sound whispered.  In all cases the mouth is opened, keeping the front teeth about one inch apart; the tongue should be in contact with the lower dental arch and lie as flat on the floor of the mouth as the production of the particular vowel sound will permit.  When this is done, and a vowel sound whispered, a distinctly resonant note can be heard.  Helmholtz and a number of distinguished German physicists and physiologists have analysed the vowel sounds in the whispering voice and obtained very different results.  If their experiments show nothing else, they certainly indicate that there are no universally fixed resonances for any particular vowel sound.  Some of the discrepancies may (as Aikin points out) be due to the conditions of the experiment not being conducted under the same conditions.  Aikin, indeed, asserts that if the directions given above be fulfilled, there will be variations between full-grown men and women of one or two tones, and between different men and different women of one or two semi-tones, and not much more.  As he truly affirms, if the tube is six inches long a variation of three-quarters of an inch could only make a difference of a whole tone in the resonance, and he implies that the different results obtained by these different experimenters were due to the faulty use of the resonator.

In ordinary conversation much faulty pronunciation is overlooked so long as the words themselves are intelligible, but in singing and public speaking every misuse of the resonator is magnified and does not pass unnoticed.  Increased loudness of the voice will not improve its carrying power if the resonator is improperly used; it will often lead to a rise of pitch and the production of a harsh, shrill tone associated with a sense of strain and effort.  Aikin claims that by studying the whispering voice we can find for every vowel sound that position of the resonator which gives us the maximum of resonance.  By percussing[A] the resonator in the position for the production of