The sound of the vowels depends, as we have seen, upon whether one or another of the over-tones takes precedence in sound. But the conditions by which the formation of the vowels is determined lie in the form of the cavity of the mouth, and of the contraction of the same in some one place or another during expiration. These places are different in different languages and dialects. They are among the English, Germans and French farthest back in sounding _a_, as in _father_; farther forward in _a_, as in _may_, _o_, _e_, in the order in which they are here placed; and farther front in the German _u_ (_oo_).
The length of the cavity of the mouth is the greatest in sounding _oo_, the least in _e_, intermediate in _a_. In the pure, clear _a_, as in _may_, or _e_ of the Germans, the cavity is the narrowest. Hence, to form a tone on this vowel is very difficult, and it is the only vowel whose pure pronunciation must be sacrificed to the tone. Good tones can be formed on this vowel when in both series of the chest register there is mingled with it the sound of the German _ö_, pronounced in English nearly like the vowel in _bird_, and in the higher registers the sound of the _e_--that is, of the German _i_. The cavity of the mouth is thus somewhat broadened, and the tone gains more room for its development.
The Swiss form the _o_ and _u_ like the _a_ in _father_, broadest at the back of the mouth, and the _e_ broadest towards the front. But the Italians form no vowel as far front as their clear sounding beautiful _a_, as in _father_; and probably because the _a_ in the Italian language sounds broadest and most distinctly, Italian wagoners drive their beasts with the shout of _a! a!_ while the Germans use for the same purpose, _hü! huo!_ and the Swiss, _hipp!_ One can only approximate an imitation of the Italian _a_ by uttering it in connection with consonants coming rapidly, as in _pfa_, _bra_, and in as short and rapid a manner as possible.
The old Italian masters naturally found their beautiful _a_ most favorable to the formation of a good tone in singing; and thus it has been adopted by other nations. But here is the very reason why a tone free from badly sounding colorings is so rarely heard. We have blindly imitated the Italians, without considering the different modes of forming the vowels in different languages and nations, and that the Italian _a_ is a vowel entirely different from the German and the similarly sounding English _a_. Its correct sound is learned by those to whom it is not vernacular only with difficulty.