The manometric flame tube, designed shortly after 1862 by the same Karl Rudolph Koenig, is a wooden open resonant tube with a square or rectangular cross section with a flute mouthpiece. Along one of the sides adjacent to the one where the mouth of the pipe is located there are three holes closed by the elastic membranes of three very small manometer capsules.
The illuminating gas reaches the capsule from a box attached to the side on which the mouth is located by means of very small brass taps and rubber connecting tubes. In each capsule, the small illuminating gas outlet pipe is equipped with a brass or glass burner in which the manometric flame burns.
Once the three flames are lit, if the pipe is made to play the fundamental, we can see that the central one oscillates rapidly while the other two remain steady. This indicates that corresponding to the central hole there is a pressure antinode and corresponding to each of the other two there is a node.
If the pipe is made to play the first harmonic of the fundamental tone, it is the central flame that remains steady while the other two oscillate, thus indicating that the positions of the nodes and antinodes have changed.
The pipe presented is 72.4 cm in length, it has a square cross section with an inner side of 6 cm and it is made of wood, except for the side opposite the mouth, which is made of glass for most of its length.
The presence of the glass side allows the carrying out of a very simple experiment when associated with the observations made with the manometer capsule. It was presented by Félix Savart (1791-1841) in 1823 and shows, with great didactic effectiveness, that a pressure antinode corresponds to a vibration node and a vibration antinode corresponds to a pressure node.

Battelli - Cardani (s. d.), Vol. II, p. 136
Boutan - D'Almeida (1867), T. II, p. 246
Daguin (1878), T. I, p. 624
Ganot(1864) ,p. 178

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