Historical Background

It has been on my mind for years to tell the history of schlieren and shadowgraph techniques in detail and proper chronological order. This story reveals a connection generally unappreciated amongst the works of several well-known fathers of technology and others not so well-known, at least not in this context. It is the story of a way of seeing the invisible, and of discoveries centuries before their time; discoveries that nonetheless eventually played an important role in far-flung branches of science and technology. Other elements of this history touch on the key role of direct observation and the almost-lost art of ingenious bench-top experiments in physics. Despite beginnings centuries ago, only now can a complete history be written — thanks in large part to the scholarship of several colleagues who have a fine appreciation of history [11–13].