Xerography or electrophotography is a dry photocopying technique. Its fundamental principle was invented by Hungarian physicist Pál Selényi and based on Selényi's publications Chester Carlson applied for and was awarded U.S. Patent 2,297,691 on October 6, 1942. The technique was originally called electrophotography. It was later renamed xerography—from the Greek roots ξηρός xeros, "dry" and -γραφία -graphia, "writing"—to emphasize that, unlike reproduction techniques then in use such as cyanotype, this process used no liquid chemicals.