Sentence:  It was April 22, 1831, and a young man was walking down Whitehall in the direction of Parliament Street.nb.... He halted opposite the Privy Gardens, and, with his face turned skywards, listened until the <WSD>sound</WSD> of the Tower guns smote again on the ear and dispelled his doubts. 
Meaning of the word marked with <WSD> tags:  A vibration capable of causing such sensations.