100

Fog-Signals and Sound Navigation

đŸ€” According to the text, what is the primary sense that fog signals appeal to?
Difficulty: Easy
🧐 According to the text, what were once considered serious obstructions to sound, but have since been scientifically proven to have no sensible power to obstruct sound?
Difficulty: Medium
đŸ€Ż What does the text suggest is the true test of a sound signal's effectiveness, rather than how far it can be heard under ideal conditions?
Difficulty: Hard