The next and the most important of the Diphthongs (except AU) is AI, compounded of the third (A) and the first (I) of the simple Vowel-Sounds. It is pronounced very nearly like the English long I, as in p_i_ne, f_i_ne, etc., which is not a _simple_ Vowel; but is compounded of the two simple Vowels above mentioned (A and I, ahee) in a very close union with each other; or, as it were, squeezed into each other. The Tikiwa (Tee-kee-wah) combination (this is the name of the Scientific Universal Language), AI, is not ordinarily quite so close, and when pronounced _long_, is quite open, so that each Vowel is distinctly heard (ah-ee). This Diphthong AI may be regarded as embracing and epitomizing the lower or ground wing or half of the Simple Vowel-Scale (I E _a_ A); its meaning is, therefore, that of BASIC or SUBSTANTIAL REALITY: the GROUND of Existence. Contrasted with this is the next Diphthong, _O_I (aw-ee), compounded of the fifth (_o_) and the first (I) Vowel-Sounds. It is the Sound of _oy_ in b_oy_. The I contained in this Diphthong may be regarded as standing in the place of U at the other extremity of the Scale. This last Sound has a tendency to return into I through the French slender U, illustrating the Principle of the Contact of Extremes. The Diphthong _O_I may, therefore, be viewed as embracing and epitomizing the upper or ethereal wing or half of the Simple Vowel Scale (_o_ _u_ O U); its meaning is, therefore, that of AERIAL or ASCENDING REALITY; LOFTINESS or LOFT. Next there occurs a Diphthong OI, pronounced as the same letters in the English word g_oi_ng, which has a half claim to be ranked with the Leading Diphthongs. It is sometimes reckoned into, and sometimes out of, the Scale--like _a_ among the Simple Vowels. Its meaning is that of FRONTNESS, PROSPECT. Finally, the great Focal Diphthong, that which includes and epitomizes the whole Vowel Scale, is AU (ah-oo), compounded of the third Vowel-Sound (A) and the Seventh (or Eighth) U. It is the sound heard in _ou_r, or in the Spanish c_au_sa. The meaning of this Supreme Diphthong and general Vowel Representative is UNIVERSAL REALITY. It stands practically in the place of all the Vowels, in the Composition of Words of an inclusive meaning. That is to say, it integrates in its signification, all that is inherently signified by all the other Vowels.