This should be practised very slowly, that the sensations may be clearly discerned, and that no vibration that gives the vowel its pitch and duration may escape attention.
The muscular contraction described comprises the chief functions of the vocal organs, and is as necessary for singing as the breath is for the tone. Year in and year out every singer and pupil must practise it in daily exercises as much as possible, on every tone of the vocal compass.
In the lowest as well as in the highest range the sharpness of the a is lost, as well as the clear definition of all single vowels. A should be mingled with oo, ah, and e. In the highest range, the vowels are merged in each other, because then the principal thing is not the vowel, but the high sound.
Even the thought of ā and ē, the latter especially, raises the pitch of the tone. The explanation of this is that ā and ē possess sympathetic sounds above the palate that lead the breath to the resonance of the head cavities.
For this reason tenors often, in high notes, resort to the device of changing words with dark vowels to words with the bright vowel e. They could attain the same end, without changing the whole word, by simply thinking of an e.
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Without over-exertion, the singer can practise the exercises given above twenty times a day, in periods of ten to fifteen minutes each, and will soon appreciate the advantage of the muscular strengthening they give. They make the voice fresh, not weary, as doubtless many will suppose.
What, then, can be expected of an untrained organ? Nothing!
Without daily vocal gymnastics no power of endurance in the muscles can be gained. They must be so strong that a great operatic rôle can be repeated ten times in succession, in order that the singer may become able to endure the strain of singing in opera houses, in great auditoriums, and make himself heard above a great orchestra, without suffering for it.