The phonetic contrasts may be classified on phonetic and acoustic grounds into five main groups. There are also two minor groups which are of less interest. In the first group the contrasting vowels belong to the series 'a', 'ä', 'ε', 'e', 'i'. The pronunciation of these vowels, as of all other vowels, was 'quantitavely uniform in a given pair' [...]
- Sapir (1929), Pag. 64

[...] 'a', 'ä', 'ε', 'e', 'i' [...] The phonetic values of these vowels were respectively those of 'a' of German 'Mann' ('a'), 'a' of English 'hat' ('ä'), 'e' of English 'met' ('ε'), 'e' of French 'été' ('e'), 'i' of French 'fini' ('i'). It will be observed that the phonetic contrast is gradually lessened within the scale as one moves from 'a' to 'i'.
- Sapir (1929), Pag. 64