SYNERESIS
Syneresis is the uniting of two or three vowels, each of which is ordinarily possessed of full syllabic value, into a diphthong or a triphthong, thereby reducing the number of syllables in the word; h does not interfere with syneresis. Thus, aérea is normally a word of four syllables. In this verse it counts as three.
Mística y aérea dudosa visión (12)
(The numbers in parentheses indicate the syllables in the verse. Remember that the figure represents the theoretical number of syllables in the line, and indicates the actual number only in the case of the verso llano. Furthermore, the figure has been determined by a comparison with adjacent lines in the same stanzas, verses which offer no metrical difficulties.) So likewise in:
Y en aérea fantástica danza (10)
In the following we have double syneresis, and the word has but two syllables:
Aerea como dorada mariposa (11)
Examples of syneresis after the tonic stress:
Rechinan girando las férreas veletas (12)
Todos atropellándoos en montón (11)