Semyon Kirlian spent decades chasing a glow.

In 1939, in his workshop, the Soviet electrician watched a spark leap between an electrode and a patient's skin during a medical demonstration. He could not let it go. He and his wife Valentina built their own apparatus, pressed leaves and hands against photographic plates, and ran high voltage through them. In every photograph, he saw a halo of light around the living thing. When a subject fell ill or grew tired, the halo dimmed, and Kirlian took that for the life force itself, caught at last on silver and gelatin. He believed it to his death.