One day in Paris, in 1827, a cer­tain Madame Daguerre approached the famous chemist Jean Dumas. Her hus­band was obsessed, she said, with an appar­ent­ly fool­ish idea. He believed he could make per­ma­nent pic­tures on met­al plates by means of light focused by a lens. Was his dream with­in the bounds of sci­ence, she asked, or was he com­plete­ly mad?