Radiation that sees through flesh and maps atoms.
Röntgen's discovery and the Coolidge tube, continuous X-rays and the cutoff wavelength, characteristic Kα, Kβ and L lines and the energy levels of an atom with an inner vacancy, intensity versus hardness, Moseley's law and the ordering of the periodic table, Bragg's law and crystal diffraction, and the properties, uses and dangers of X-rays.