Flame manometer

From Ccpi

The manometric flame apparatus was first invented by Rudolph Koenig in 1862, and was used throughout the field of acoustics prior to the development of more precise methods of examining the shape of sound waves, such as the phonodeik or modern oscilloscopes. A sound wave is channeled through a rubber tube, which connects to one side of an enclosed capsule. The capsule is bisected by a rubber diaphragm. On the other side, flammable gas is flowing to the flame. The rubber diaphragm acts a modulator for the gas, oscillating with the sound wave.