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Hatha yoga is a system of yoga introduced by Yogi Swatmarama, a Hindu sage of 15th century India, and compiler of the Hatha Yoga Pradipika.

"The word "hatha" comes from the Sanskrit terms "ha" meaning "sun" and "tha" meaning "moon". Thus, Hatha Yoga is known as the branch of Yoga that unites pairs of opposites referring to the positive (sun) and negative (moon) currents in the system."

Swatmarama introduces his system as preparatory stage of physical purification that the body practices for higher meditation or Yoga. It is based on asanas (postures) and pranayama (breathing techniques, also known as shatkarma). Hatha Yoga became popular in the west beginning in the second half of the 20th century, and is often referred to simply as "Yoga" in the context of health and physical exercise.

According to unverifiable sources, while Atkinson was in Chicago at the World's Columbian Exposition in 1893, he met one Baba Bharata, a pupil of the late Indian mystic Yogi Ramacharaka (1799 - c.1893). As the story goes, Bharata had become acquainted with Atkinson's writings after arriving in America, the two men shared similar ideas, and so they decided to collaborate. While editing New Thought magazine, it is claimed, Atkinson co-wrote with Bharata a series of books which they attributed to Bharata's teacher, Yogi Ramacharaka. This story cannot be verified and—like the "official" biography that falsely claimed Atkinson was an "English author" -- it may be a fabrication.

~from Wikipedia