Music: Diabolical Sirens

To judge by their recent complaints, the people of England hate the air-raid alarms more than they hate air raids. Last week the Ministry for Home Security bowed to the popular will, reduced as much as it could the time of sounding each alarm— from two minutes to one.

No haphazard noisemakers are Britain’s wailing sirens. Sounded by air pressure operating on electric oscillators, they produce a discord which in the Middle Ages was regarded as the work of the devil. This discord is the augmented fourth (example: C and F sharp on the piano), was called the tritone because it spans three whole tones. The tritone was banned in sacred music, thus giving rise to a maxim: Mi contra fa est diabolus in musica (The tritone is the devil in music). When the sirens, beginning on a sweet major third or fifth, slip up and down into the bloodcurdling tritone, it sounds that way to Londoners.