J.J. Thomson Science lecturers who traveled from town to town in the middle nineteenth century delighted audiences by showing them the ancestor of the neon sign. They took a glass tube with wires embedded in opposite ends . . . put a high voltage across . . . pumped out most of the air . . . and the interior of the tube would glow in lovely patterns. In 1859 a German physicist sucked out still more air with an improved pump and saw that where this light from the cathode reached the glass it produced a fluorescent glow. Evidently the cathode emitted some kind of ray that was illuminating the glass. What could these rays be? One possibility was that they were