“But the Mundak Upanishad” says Weber, “refers to the half _Mátrá_ (mora), to which the word _Om_ here appearing in its full glory, is entitled in addition to its three _Mátrás_ (morae) a. u. m. This is evidently a later addition by some one who did not like to miss the mention of the subject in the Atharvana Upanishad in which it occurs.” p. 160. Again says he—“The Mándukya Upanishad which treats of the three and half _Mátrás_ of the word _Om_, is to be looked upon as the real Mándukya, all the rest is the work of the _Gaudapáda_, whose pupil _Govinda_ was the teacher of Sankaráchárya about the seventh century A. D.” [Sidenote: 5. Om the Pentad.] We find next a quinquiliteral figure of _Om_ in its component parts of the three mátrás, m, and the _bindu_ or चन्द्र बिन्दु the fifth. [Sidenote: 6. Om the Hexad.] And then again with a sextuple or Hexaliteral _Om_ composed of the sixth member of _Náda_ (नाद) over and above the aforesaid five parts. [Sidenote: 7. Om the Heptad.] The septuple Om is described in the Ramatápaniya upanishad as consisting of अ, उ, म, नाद, बिन्दु, शक्ति and नम । Weber’s A. S. Lit. p. 312. [Sidenote: 8. Om the Octad.] This consists of the aforesaid seven parts, which together with Sánti called in Persian Sákat complete the number, Weber. Id. p. 315. IV. THE DIFFERENT DENOMINATIONS OF OM. [Sidenote: 1. The Initial of the Veda.] The _om_ is denominated the heading of the Veda (बेदशिरः) as the Gáyatrí hymn is termed to be its parent (बेदमाता). It stands at the top (शिरस्) of every book (मण्डल), chapter (अष्टक), and hymn (ऋच्) of every Veda either alone by itself or two or three _oms_ put together, as ओमग्निमीले _on ignem aiede_ of the Rigveda, ॐ त्रिसप्ता _On triseptem_ &c. of the Atharvan; again ॐ ॐ ॐ ऋग्वेदाय स्वाहा _on_ I salute thee O Rigveda &c. It is hence used at the head (शिरस्) of every book on any branch of knowledge (बिद्या) which is a paronym of and derived from the same root (बिद् Video) with Veda (बेद्). The Tantra calls it as the heading of the Gáyatrí which begins with the syllable; तसेतन्महा गुह्यं गायत्र्याः शीर्षमुच्यते । ॐ भूर्भुबः स्वरित्यादिः । गायत्रीतन्त्रं ॥ [Sidenote: 2. The sacred Syllable. पूर्णाक्षरं] It is called the sacred syllable because it is used in sacred writings and in the sacred Vedic and Sanskrit languages only, and never in the popular vernacular tongues, which are known as unsacred and impure (असंस्कृतं). Moreover it is used in sacerdotal functions of the sacerdotal class (संस्कारेसंस्कृतात्मनां ) or regenerate classes of men, and never by the impure Súdra on pain of damnation (ॐकारोच्चारणाद्धोमात् श्रुद्रोहिनरकंब्रजेत्), unless he is sacrified by investiture of the sacred or sacrificial thread, (यज्ञोपवीतं). Thus says the Sástra; श्रुद्रोऽपि अधीकारीस्यात् यज्ञसूत्रप्रदानतः । गायत्री तन्त्रं, ४र्थ पटलः ।