AUGUST 12, 1915] 
NATURE 
645 

It follows that the amplitude of any term in a 
sine curve deduced from only a moderate number of 
observations must be received with caution until an 
investigation of its probable error has been made, and 
this remark refers especially to the second and higher 
terms where the amplitudes are so often small. 
W. H. Dives. 
Benson Observatory, Wallingford, July 29. 

ON THE CHARACTER OF THE “S” 
SOUND. 
Soke 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.” 1 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, 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 (A) equal to 25 mm., with good 
agreement on repetition. A hiss which I gave was 
graver and less definite, corresponding to A=32 mm. 
The frequency would be of the order of 10,000 per 
second, more than 5 octaves above middle C. 
Among the replies, publicly or privately given, 
with which I was favoured, was one from Prof. 
E. B. Titchener, of Cornell University,? who 
wrote :— 
Lord Rayleigh’s sound more like an f than an s is 
due, according to Kohler’s observations, to a slightly 
too high pitch. A Galton whistle, set for a tone of 
8400 v.d., will give a pure s. 
It was partly in connection with this that I re- 
marked later? that I doubted whether any pure 
tone gives the full impression of an s, having often 
experimented with bird-calls of about the right 
pitch. In my published papers I find references 
to wave-lengths 31°2 mm., 1304 in. =33°I1 mm., 
1°28 in. = 32°5 mm.° It is true that these are of a 
pitch too high for Kéhler’s optimum, which at 
ordinary temperatures corresponds to a wave- 
length of 406 mm., or 1°60 inches; but they agree 
pretty well’ with the pitch found for actual hisses 
in my observations with Enock. 
Prof. Titchener has lately returned to the sub- 
ject. In a communication to the American 
Philosophical Society ® he writes :— 
It occurred to me that the question might be put 
to the test of experiment. The sound of a Galton’s 
whistle set for 8400 v.d. might be imitated by the 
1 NaTuRE, vol. xci., p. 319, 1913. 
2 Phil. Mag., vol. xvi., p. 235, 1908. 
3 NaTurE, Vol. xci., p. 451, 1913- 
4 Nature, vol. xci., p. 558, 10173- 
5 Scientific Papers, I., p. 407 ; II.. p. 100. 
6 Proceedings, vol. liii., August—December, 1914, p- 323. 
NO. 2389, VOL. 95| 
Scientific Papers, V., p. 486. 

mouth, and a series of observations might be taken 
upon material composed partly of the natural (mouth) 
sounds and partly of the artificial (whistle) tones. If 
a listening observer were unable to distinguish be- 
tween the two stimuli, and if the mouth sound were 
shown, phonetically, to be a true hiss, then it would 
be proved that the whistle also gives an s, and Lord 
Rayleigh would be answered. 
The experiment was more troublesome than I had 
anticipated; but I may say at once that it has been 
carried out, and with affirmative result. 
A whistle of Edelmann’s pattern (symmetrical, 
like a steam whistle) was used, actuated by a 
rubber bulb; and it appears clear that a practised 
operator‘was able to imitate the whistle so success- 
fully that the observer could not say with any 
certainty which was which. More doubt may 
be felt as to whether the sound was really a fully 
developed hiss. Reliance seems to have been 
placed almost exclusively upon the position of 
the lips and tongue of the operator. I confess 
I should prefer the opinion of unsophisticated 
observers judging of the result simply by ear. 
The only evidence of this kind mentioned is in a 
footnote (p. 328): ‘Mr. Stephens’ use of the 
word ‘hiss’ was spontaneous, not due to sug- 
gestion.” I have noticed that sometimes a hiss 
passes momentarily into what may almost be 
described as a whistle, but I do not think this 
can be regarded as a normal s. 
Since reading Prof. Titchener’s paper I have 
made further experiments with results that I 
propose to describe. The pitch of the sounds 
was determined by the sensitive flame and sliding 
reflector method, which is abundantly sensitive 
for the purpose. The reflector is gradually drawn 
back from the burner, and the positions noted in 
which the flame is unaffected. This phase occurs 
when the burner occupies a node of the 
stationary waves. It is a place where there is 
no to and fro motion. The places of recovery 
are thus at distances from the reflector which are 
(odd or even) multiples of the half wave-length. 
The reflector was usually drawn back until there 
had been five recoveries, indicating that the 
distance from the burner was now 5x#4A, and 
this distance was then measured. 
The first observations were upon a whistle on 
Edelmann’s pattern of my own construction. 
The flame and reflector gave \=1'7 in., about 
a semi-tone flat on Kéhler’s optimum. As _ re- 
gards the character of the sound, it seemed to 
me and others to bear some resemblance to an 
s, but still to be lacking in something essential. 
I. should say that since my own hearing for s’s 
is now distinctly bad, I have always confirmed 
my opinion by that of other listeners whose hear- 
ing is good. That there should be some: resem- 
blance to an s at a pitch which is certainly the 
predominant pitch of an s is not surprising; and 
it is difficult to describe exactly in what the de- 
ficiency consisted. My own impression was that 
the sound was too nearly a pure tone, and that if 
it had been quite a pure tone the resemblance to 
an s would have been less. In subsequent ob- 
servations the pitch was raised through 
