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Vocal gas alarm tested .

Vocal gas alarm tested . _x000D_
Test are being made at Hendon to discover the best warnings in the event of a gas attack from the air . _x000D_
Sirens are being sounded separately from Hendon Police station , which is in the centre of a ring of observers , policemen the stationed in pairs at distances of 100 , 200 , 300 , 400 yards away . They have sound recording instruments to determine the po…