We shall therefore proceed with caution, and offer only what may be most useful, and most necessary for the student.

The field of discussion may be much limited if we first define what we mean by the word "dipthong."

The best definition we can find, and the one most suited to the nature of the dipthong, is, we think, that of Mr Smith, in Walker. "A dipthong," he says, "I would define to be two simple vocal sounds uttered by one and the same emission of breath, and joined in such a manner that each loses a portion of its natural length; but from the junction produceth a compound sound equal in the time of pronouncing to either of them taken separately, and so making still but one syllable."

Following this definition, three tests for a dipthong suggest themselves.

1. The emission of the two sounds by the same breath.

2. Their amalgamation, or more correctly, their coalescing; for each vowel in the Maori dipthong is distinctly heard.

3. The abbreviation of the natural length of each simple sound.

In applying these rules to the dipthongs, it will be perhaps most prudent to divide them, under the present imperfect state of our knowledge, into two classes. 1. The certain, or those of the dipthongal character of which there can be but little question. 2. The doubtful, or those upon which inquirers may be likely to entertain different opinions.

The dipthongs which we consider certain, are as follows: