The very first X-ray device was discovered accidentally by the German scientist Wilhelm Röntgen (1845-1923) in 1895. He found that a cathode-ray tube emitted certain invisible rays that could penetrate paper and wood and, the first person in the world to see through human flesh, even saw a perfectly clear outline of the bones in his own hand. Röntgen studied these new rays--which he called X-rays--for several weeks before publishing his findings in December of 1895. For his great discovery, he was given the honorary title of Doctor of Medicine and awarded the 1901 Nobel Prize for physics. Adamant his discovery was free for the benefit of humankind, Röntgen refused to patent it.

X-rays are waves of electromagnetic energy which behave in much the same way as light rays, but at wavelengths approximately 1000 times shorter than the wavelength of light. X-rays can pass...