25. The 3 Merits. Of the meditation of the three letters of Om described at length in the Upanishads.
XII. The Tetrads Or Quadruples of Om.
I. Tetrads of Om. We have next to consider the tetrads or quadruple divinities in the quadrants or four fold divisions of the circle of Om consisting of its four letters a, u, or crescent of Om, and the circlet of entire Om styled Chandravindu as given by Professor Monier Williams from the Nirukta of yaska. (Indian Wisdom p. 169).
II. In sciences. 1. The Om of orthographers consisting of the four stages of speech; namely, ध्वनि पश्यन्ती मध्यमा and बैस्वरी ।
2. Of Grammarians; the four parts of speech, nouns, verbs, prepositions and particles.
3. Of Ritualists; The hymns, liturgical precepts, Bráhmanas and ordinary language.
4. Of philologers or Sábdikas; the speech of serpents, beasts, birds and vernaculars.
5. Of Etymologists; The Rik, Yajur and Sáma Vedas and current language.
6. Of Spiritualists; The language of beasts, wild animals, musical instruments and soul.
7. Of Manu (IV. 126). The Pranava and the three Vyahrtis. (ॐ भूर्भ्रुवः स्वर्).