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The Spike: or, Victoria University College Review, October 1917

The Sound of the Cannon

The Sound of the Cannon

The heavy bombardments in Belgium during the first year of the war have led to interesting investigations on the transmission of sound. Bigourdau, the French astronomer, has drawn an "audibility" map for the French region, based upon exhaustive personal inquiries, and chiefly directed towards discovering the maximum distances at which the bombardments, e.g. of Antwerp were heard along a line extending from the Swiss frontier to the Channel. Similar investigations undertaken in Holland and Belgium under the direction of Van Everdingen director of the Utrecht Meteorological Observatory, revealed the fact, hitherto unexplained, that the cannon of Antwerp, which could be heard distinctly in the extreme north of Holland, were totally inaudible throughout an annular zone of a uniform width of about 37 miles, the inner circumference of which starts at a uniform distance of about 53 miles from Antwerp. In other words, up to 53 miles from the besieged city, the bombardment was heard in all directions, the evidence being detailed and complete except as regards the portion of the circle covered by the sea, with regard to which the evidence is necessarily fragmentary. Then, for a further distance of 37 miles in all directions, no evidence of audibility could be found; but outside this "zone of acoustic darkness," as Van Everdingen calls it, the cannon was again audible up to a distance of some 112 miles (the extreme limit of Dutch territory) in the North, and in France up to a maximum distance of between 180 and 190 miles (Bigourdau). Bigourdau became aware in the course of his investigations of Van Everdingen's "zone of acoustic darkness," and obtained confirmatory results in Northern France.

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The attention of Van Everdingen was first drawn to the remarkable phenomenon of his "zone" by the fact that while Antwerp was under fire not a sound could be heard at his own home, Utrecht, while the Dutch newspapers teemed with accounts of the bombardment being heard at localities far more distant. At later date when German heavy guns moved 50 miles or so further south, they were distinctly heard at Utrecht, the whole zone of acoustic darkness having shifted. The extraordinary nature of these facts led Van Everdingen, and Subsequently Bigourdau as regards Northern France, to organize systematic inquiries, which have enabled the exact dimensions of the zone to be ascertained. The evidence is complete, except as regards the small portion of the zone falling in German territory.

The scientific explanation of the phenomenon should afford an interesting problem for students of physics.

The accompanying sketch plans show:—

No. I. : Zone area established by Van Everdingen. Of maximum audibility (for 1914-5) established by Bigourdau for France.

Map of France and Belgium showing firing line 1914-15

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No. II. :Zone area established by Van Everdingen. The shadow portion is the area of "Acoustic Darkness."

Map of Belgium showing area of 'Acoustic darkness'