X-rays were discovered by accident. While experimenting with cathode rays covered by thick cardboard in 1895, Wilhelm Röntgen noticed a light being cast on a fluorescent board across the room. The first X-ray was of the hand of his wife, who saw the image of her bones and exclaimed ‘I have seen my death!’ – so he named them X-rays, using an ‘X’ to represent their mysterious nature. Source Source 2 Source 3