Even in the past reports, the unusual sounds were normally thought to arise in the vicinity. I think it possible that the Barisal guns, and similar phenomena, are the sounds of thunder carried by anomalous propagation over several hundred kilometers to the points where they are heard. In many cases, the sound is described as much like thunder, and to come from the direction of the horizon, with no apparent source, and often in multiple, all of which is characteristic of noises heard by anomalous propagation.

Anomalous Sound Propagation

Very little was known about the upper atmosphere in the years immediately following the World War. The lapse rate in the troposphere was well known from balloon and aircraft ascents. The stratosphere had been discovered by Teisserenc de Bort in 1899,a zone of anomalous audibility to the east, but none to the west. In the summer, when the winds were reversed, the zone of audibility was moved to the west. On occasion, a second zone of silence and a second zone of anomalous audibility were observed, the sound making a double skip. Surface winds will have no strong effect, except in the launching of the wave.

At the time, there was no way of investigating the upper atmosphere directly. Balloons could only ascend to the stratosphere. Therefore, anomalous propagation of sound became of great interest as a means of probing the upper atmosphere. In 1923, a series of large explosions was set off from La Courtine in central France. These were the first experiments in which accurate time measurements