304 S. Porter on the Vowel Elements in Speech. 
the impulse, after reaching the closest degree, would be to raise, 
or bend up, the tongue at a point further forward, and so to carry 
the vowel into another group. The middle may, however, 
sometimes take the course of the open degree, and move a step 
backward in becoming more close when prolonged. 
The tendency of the open-depressed vowels, when prolonged, 
is, for like reasons, in the opposite direction: they incline to 
greater openness, so far as possible, or else to a backward move- 
ment. Thus, self, ten, &c. drawled into the open-depressed de- 
gree, incline to the @ if still further prolonged. 
t is to be remarked, that the turn taken by vowels under 
change of quantity will be much influenced by the character of 
consonants succeeding. 
ese physiological actions and tendencies are important in 
their bearing upon vowel change in etymology, and as explain- 
ing the rationale of diphthongs and all compound vowel sounds. 
This will presently be illustrated by examples. 
the relations among the several vowels depend. 
A number of different series may be made out, founded on 
a, e, tand a, o, uw. 
ward on the line of the tongue, from the common point of de- 
