The story of the development of a device of a distinctively new order, from its first inception to its practical reality, adds a human interest to its description which is perhaps too often lacking among scientific records. In 1900 when I was beginning experiments on the electrolytic responder, it was my good fortune to have to work upon it at night in my own room, at a table beneath a solitary gas-burner with Welsbach mantel. My source of hertzian waves was the discharge of a small induction-coil placed in an opposite corner and set into operation by a key closed by pulling a string.