Note 11 — Chapter XXII · THE ARTICULATION OF THE ITALIAN CONSONANTS; SPEAKING EXERCISES FOR A CORRECT VOICE PRODUCTION
Reading edition
Dr. Mills says that S cannot be sounded without more or less of a hissing sound, suggesting the escape of air, which is very unpleasant to the ear; and unfortunately these hissing sounds are very common in English, so that the speaker or singer is called upon to use all his art to overcome this disagreeable effect.