|Physics 335, Lecture 1 / slide 01-05|
The spectra of hot gasses consist of lines of color, which means that atoms seem to be more-or-less equivalent to a clock tower. A clock tower can only give off certain frequencies of sound, corresponding to the bells within, and atoms can only give off only certain frequencies of light, corresponding to --- ?? Well, the physicists of 1890 weren't quite sure. They supposed that the atoms were vibrating somehow, to create the light.