The first published mention of the term was in the 1963 surf guitar instrumental "Soul Surfer", by the Southern California surf guitarist Johnny Fortune. The song was intended to reference the then-current soul music genre. The term "soul surfing" gained popularity in the late '60s, with the phrase most used in the mid- and late-'70s. In 1969 theologian Tom Blake penned an article entitled "Voice of the Wave", which examined the religious elements of surfing. By the early 70s, curious surfers began to experiment with various Eastern philosophies, such as yoga and meditation.