Dr. Olsen, one of the team of scientists from the Johns Hopkins Applied Physics Lab, briefly discusses the history of fire. He explains the zones and structure of a candle's flame and uses the Schlieren system of photography to detect the density gradients in the rising gas. Capt. Gayhart discusses the study of early spark-ignited flames, and he diagrams the operation of the Schlieren system. Mr. Edmondson shows three films of a flame's development in a stream of combustible gas taken at 100,000, 20 million, and 200 million frames per second.