The 'X' in 'X-rays' stands for 'unknown'
German physicist Wilhelm Conrad RÃ¶ntgen accidentally discovered a new form of radiation in 1895 while testing if cathode rays could pass through glass and dubbed them 'X-rays' because of their "unknown" nature. He later printed the first "medical" X-ray, which shows his wife's hand and a ring. RÃ¶ntgen, born on March 27, 1845, won the first-ever Physics Nobel in 1901.