Some two years ago I asked for suggestions as to the formation of an artificial hiss, and I remarked that the best I had then been able to do was by blowing through a rubber tube nipped at about half an inch from the open end with a screw clamp, but that the sound so obtained was perhaps more like an f than an s. “There is reason to think that the ear, at any rate of elderly people, tires rapidly to a maintained hiss. The pitch is of the order of 10,000 per second.” The last remark was founded upon experiments already briefly described under the head “Pitch of Sibilants.”

“Doubtless this may vary over a considerable range. In my experiments the method was that of nodes and loops (Phil. Mag. Vol. VII. p. 149 (1879); Scientific Papers, Vol. I. p. 406), executed with a sensitive flame and sliding reflector. A hiss given by Mr Enock, which to me seemed very high and not over audible, gave a wave-length (λ) equal to 25 mm., with good agreement on repetition. A hiss which I gave was graver and less definite, corresponding to λ = 32 mm. The frequency would be of the order of 10,000 per second, more than 5 octaves above middle C.”