Pre-eminently long by nature are the diphthongs ai, oi, ae, and the rest, for the reason that essentially--whatever our modern schoolmaster may say to the contrary--they are themselves a twofold, concrete tone, which combines, much as green does among the colours. The long-sounding vowels are equally so. As a third principle, which obtains already in Sanscrit, no less than the Greek and Latin languages, we have associated with them peculiar conditions of position. In other words, if two or more consonants are placed between two vowels the relation constitutes what is unquestionably a difficult transition in speech. The organ of articulate utterance requires a longer period to pass over the consonants; this necessitates a pause which, despite of the presence of the short vowel, makes the syllable sound in its rhythm long, though it is not actually lengthened. If I speak the words for example_--mentem nec secus_--the movement from the one vowel to the other in _mentem_ and _nec_ is neither as simple or easy as in _secus_. More modern languages do not retain this last distinction with such stringency, but rather give effect, in the matter of long and short accent, to other criteria. But for all that syllables which are treated as short, despite of the position referred to, at least will not unfrequently create a harsh impression, because they obstruct the quicker movement our ear demands. In contradistinction to the long quantity we have in diphthongs, long vowels and length created by position, we have the vowels which are by nature _short_, that is, those which are short, or which are not placed in words, where one of them and another immediately following are separated by two or more consonants.