From a historical perspective, the New Age phenomenon is most associated with the counterculture of the 1960s. According to author Andrew Grant Jackson, George Harrison's adoption of Hindu philosophy and Indian instrumentation in his songs with the Beatles in the mid 1960s, together with the band's highly publicised study of Transcendental Meditation, "truly kick-started" the Human Potential Movement that subsequently became New Age. Although not common throughout the counterculture, usage of the terms "New Age" and "Age of Aquarius" – used in reference to a coming era – were found within it, for instance appearing on adverts for the Woodstock festival of 1969, and in the lyrics of "Aquarius", the opening song of the 1967 musical "Hair: The American Tribal Love-Rock Musical".