Living Pictures

THE scientist engaged on practical research and experiment has to be something of an engineer and, indeed, of an inventor. An interesting example of the need for this kind of approach to a problem is afforded by the account of the evolution of the ingenious method of obtaining actual film records of shock waves in action, so to speak, which appears in this issue. The whole matter arose, we believe, from the fact that pilots reported observing the appearance at high speeds of lights, or bands of light, on the wings of their aeroplanes; which it seemed possible were due to the formation of shock waves rendered visible by the refraction of light.