How can this be done? _A_ and _e_ are bright vowels, must be sung with a pleasant, almost smiling, position of the mouth. _U_ and _o_, on the contrary, are dark vowels, for which the lips must be drawn into a sort of spout. Look at the position of the throat in these vowels: (1) as they are usually sung and spoken; (2) as I feel it, in singing, as I sing them, and as they must be sung and felt.
How do I connect them with each other? If I wish to connect closely together two vowels that lie near to or far from each other, I must first establish the muscular contractions for _[=a]_, and introduce between the two vowels, whether they lie near together or far apart, a very well-defined _y_. Then (supposing, for instance, that I want to connect _[=a]_ and _[=e]_) I must join the _[=a]_ closely to the _y_, and the _y_ closely to the _[=e]_, so that there is not the least resonating space between the two that is not filled during the changes in the position of the organs, however carefully this is undertaken. There must be no empty space, no useless escape of breath, between any two of the sounds.
At first only two, then three and four, and then all the vowels in succession must be so practised:--
_A-ye, a-ye-yu, a-ye-yoo-yü, a-ye-yo-yü-yu-ye-yah._
But there must be never more than so much breath at hand as is needed to make the vowel and the tone perfect. The more closely the vowels are connected with the help of the _y_, the less breath is emitted from the mouth unused, the more intimate is the connection of tone, and the less noticeable are the changes of the position of the organs in relation to each other.
When I pass from _y[=a]-y[=e]_ to _yoo_, I am compelled to develop very strongly the muscular contraction of the lips, which are formed into a long projecting spout; and this movement cannot be sufficiently exaggerated. With every new _y_ I must produce renewed muscular contractions of the vocal organs, which gradually, through continuous practice, are trained to become almost like the finest, most pliable steel, upon which the fullest reliance may be placed. From _yoo_ it is best to go to _yü_, that lies still farther forward and requires of the lips an iron firmness; then to _yo_, touching slightly on the _e_ that lies above the _o_; then return to _y[=a]_, and not till then going to _ye-ah_, which must then feel thus:--