Yogananda, in Autobiography Of A Yogi (1971), defines mantra as a "potent vibratory chant." He further stated, "The literal translation of Sanskrit mantra is 'instrument of thought.' It signifies 'the ideal, inaudible sounds which represent one aspect of creation; when vocalized as syllables, a mantra constitutes a universal terminology.' (Webster's New International Dictionary, 2nd ed.) The infinite powers of sound are derived from Aum, the 'Word' or creative hum of the Cosmic Motor." (Yogananda, 470 footnote)

In describing the significance of mantra japa [japa means repetition], Yogananda explained, "The potencies of sound and of vach, the human voice, have nowhere else been so profoundly investigated as in India. The Aum vibration that reverberates throughout the universe (the 'Word' or 'voice of many waters' of the Bible) has three manifestations or gunas, those of creation, preservation, and destruction (Taittiriya Upanishad I:8). Each time a man utters a word he puts into operation one of the three qualities of Aum. This is the lawful reason behind the injunction of all scriptures that man should speak the truth." (Yogananda, 20 footnote)

"The ancient rishis discovered these laws of sound alliance between nature and man. Because nature is an objectification of Aum, the Primal Sound or Vibratory Word, man can obtain control over all natural manifestations through the use of certain mantras or chants." (Yogananda, 163)

"...The Puranas (ancient shastras or treatises) describe these mantric wars between devas and asuras (gods and demons). An asura once tried to slay a deva with a potent chant. Because of the mispronunciation the mental bomb acted as a boomerang and killed the demon." (Yogananda, 418 [footnote])

At http://education.yahoo.com/reference/encyclopedia/entry?id=47744, the description of transcendental meditation is as follows: It is a "religious movement based on Vedanta philosophy, founded by Maharishi Mahesh Yogi. Stressing natural meditation and the liberating pleasures such practices could invoke, the method is believed to help individuals achieve a higher level of consciousness. Brought by Maharishi from India to the West in 1959, transcendental meditation was a distinct subculture within the 1960s youth movement, attracting actress Mia Farrow, cultural philosopher Marshall McLuhan, and the Beatles, who eventually rejected the Yogi's teachings."