Acoustic shadow

Such conditions enable sound to travel in refraction channels over long distances until returning to the Earth's surface, and it thus may not be heard in intervening locations.

[3] Many other instances of acoustic shadowing were prevalent during the American Civil War, including the Battles of Seven Pines, Gaines' Mill, Perryville and Five Forks.

[5] Two diarists John Evelyn and Samuel Pepys heard from London the naval guns of the Four Days' Battle, which ranged over the southern North Sea between England and the Flanders coast.

However the guns were not heard at all in towns on the coast nearer to the action:[1] Being in my garden at 6 o'clock in the evening, and hearing the great guns go thick off, I took horse and rode ...next day toward the Downs and seacoast, but meeting the Lieutenant of the Hampshire frigate, who told me what passed, or rather what had not passed, I returned to London, there being no noise, or appearance at Deal, or on that coast of any engagement.

Recounting this to his Majesty...he was astonished when I assured him they heard nothing of the guns in the Downs, nor did the Lieutenant who landed there by five that morning.