After consideration of Yoga the title of our work, and all its component parts tending to the exercise of meditation, together with an investigation into the nature of _Átman_ or soul, as the agent of the act of meditating and procuring its salvation, we are led by a natural and coherent train of thought to an inquiry into the nature of that grand object of our holy and profound meditation, which is the only means of our emancipation, and which is presented at once to our view in the exordium of the work in the mystical characters of _Om Tat Sat = On Id Est_. [Sidenote: 2. Ambiguity of the word _Om_.] The word _Om_ forming the initial of the said epigraph standing prominent at the top of the opening page of the work, and being more than a multinymous term and ambiguous in its acceptations, requires to be treated at some length, in order to discover the hidden meaning lying buried under that mystic emblem of the grand arcanum of Brahmanical and Universal religion, from amidst a variety of significations which are heaped upon it in the sacred writings and holy speculations of the early sages of India. THE SRUTI SAYS:— [Sidenote: 3. In the beginning was the word _Om_.] ॐमित्येवमग्रमासीत् । प्रथम मोङ्कारात्मकमासीत् । तस्माच्च निःसृताः सर्ब्बे, प्रलीयन्ते तत्रवै । So saith the Holy scripture:— “In the beginning was the word, the _word_ was with God, and the _word_ was God. All this was made by him, and without him was not anything made, that was made and” St. John 1.1-3. [Sidenote: Om, the light of the world.] And again says the Sruti दीप्यतोँ ज्योतिः । तत्तेजोऽनेनैवोमित्येव तदुद्बुध्न्यति । मैत्री उप ७ ।११ “That _Om_ shone forth as light, but they received it not, and hid it in darkness.” So the Scripture:— “That was the light of the world, and the light shone upon the world, but the world knew it not &c.” St. John, Ch 1, V. 5. 9. 10. [Sidenote: 5. Its Revelation to mankind.] Again says the Scripture:—“God sent one to bear witness of the light, that all men through him might believe.” Id 1.7. So Brahmá the god revealed its meaning to his first begotten son _Atharvan_, and Atharvan, the Prajápati, gave instruction on the subject to _Pippaláda_, _Sanatkumára_ and _Angira_ (Weber A. S. L., p. 164). Again _Angiras_, who communicated it to _Saunaka_, had obtained it from Bharadvája Satyaváha, and the latter again from _Ángira_, the pupil of _Atharvan_, to whom it was revealed by _Brahmá_ himself (Weber A. S. L., p. 158). [Sidenote: 6. Works on its Disquisition.]