The sacredness of the word _Om_, as the expression for the eternal position of things, is specially emphasised in the Katha Upanishad (Weber. p. 158). [Sidenote: 3. The Holy syllable पबित्रं] It is held as the most holy syllable being an appellation of the Most High, and must not be uttered in unholiness even by the holy orders of men: so says the Katha Up;—“This is the most holy syllable, this the supreme syllable, whosoever knoweth this syllable getteth whatever he desireth.” (Cowell’s Maitrí Upanishad. Ch. VI. S. 4) note. [Sidenote: 4. The Mystic Syllable गुह्यं] This is styled the mystic syllable because the most recondite and abstruse doctrines of Brahmanical theism are hidden under its symbolical garb, and form the foundation of those wonderful structures of the mystic poetry and philosophy of nations, which have been beautifully illustrated by Sir W. Jones in his “Mystic Poetry of the Hindus, Persians, and Greeks.” It was this mysticism which invited a Pythagoras of old to India. Manu says;—“He knows the Veda, who distinctly knows the mystic sense of this word.” Chap XI. 266. These senses are recommended to be deeply studied by the Upanishads themselves, saying;—“The _om_ is a subject of deep study” (Web. p. 163), and forms of itself “as another triple Veda.” (Manu XI. 265). It is enjoined to be carefully kept in secrecy by the Tantras and Smritis. तत्त्वमेतन्महा गुह्यं गायत्र्याः कुक्षिरुच्यते । तदेन्महामन्त्रं गोप्यं गोप्यं हि यत्नतः ॥ [Sidenote: 5. The Mysterious syllable गूढ़ाक्षर] _Om_ again as a symbol of the eternal position of things प्रकृतिः कुण्डालाकारा, presents to us a mysterious round of the mystic dance of myriads of spheres, emitting an inaudible sound reaching beyond its utmost limit to the unknown One who sitteth above the circumference of its visible horizon; or as the sacred writer expresses it; “He that sitteth on the circle of the earth.” Isaiah. Chap. X. 1. The Tantra speaks of its encompassing the world; ब्यापकत्वादि तत्त्वाच बिन्दुस्तेनैब कथ्यते, अनुस्वारस्वरूपासा बिन्दुरुपाचिदाकृतिः । गायत्रीतन्त्रं । [Sidenote: 6. The sphere of sound नादबिन्दुः] That _om_ contains within it the whole sphere of sounds (नाद) is beautifully illustrated in twenty slokas or stanzas in an Upanishad of that name the नादबिन्दूपनिषद् । (Weber, p. 165). It shows how the eternal sound _om_ emitted by _Brahma_ pervaded throughout the Universe, and the manner in which all other sounds are propelled by continual vibrations of air like curves upon the surface of water (बीचितरङ्गन्यायेन) to the auditory of the other. The _Vindu_ is a _Mudrá_ in Tantra ब्यपकत्त्वाद्बिन्दुमुक्तं । कुण्डलिनी स्वार सर्ब्ब ब्यापिनी । Compare the Pythagorean music of the spheres. [Sidenote: 7. The Focus of light तेजो बिन्दुः ।]