646 
oNe=sits) “shel 
impressions. 
Wishing to try other sources which I thought 
more likely to give pure tones, I fell back on 
bird-calls. A new one, with adjustable distance 
between the perforated plates, gave on different 
trials X=1°8 in., A=1°6 in. In neither case was 
the sound judged to be at all a proper s, though 
perhaps some resemblance remained. The effect 
was simply that of a high note, like the squeak 
of a bird or insect. Further trials on another 
day gave confirmatory results. 
The next observations were made with the 
highest pipe from an organ, gradually raised in 
pitch by cutting away at the open end. There 
was some difficulty in getting quite high enough, 
but measures were taken giving A=2'2 in., 
X=1'9 in., and eventually A=1°6 in. In no case 
was there more than the slightest suggestion of 
an S. 
As I was not satisfied that at the highest pitch 
the organ-pipe was speaking properly, I made 
another from lead tube, which could he blown 
from an adjustable wind nozzle. Tuned to give 
X}=1'6 in., it sounded faint to my ear, and con- 
veyed no s. Other observers, who heard it well, 
said it was no s. 
In all these experiments the sounds were main- 
tained, the various instruments being blown from 
a loaded bag, charged beforehand with a foot 
blower. In this respect they are not fully com- 
parable with those of Prof. Titchener, whose 
whistle was actuated by squeezing a rubber 
bulb. However, I have also tried a glass tube, 
1o0°4 in. long, supported at the middle and rubbed 
with a resined leather. This should be of the 
right pitch, but the squeak heard did not suggest 
an s. I ought perhaps to add that the thing 
did not work particularly well. 
It will be seen that my conclusions differ a good 
deal from those of Prof. Titchener, but since 
these estimates depend upon individual judgment, 
perhaps not uninfluenced by prepossessions, they 
are not fully satisfactory. Further independent 
aural observations are desirable. I fear a record, 
or ocular observation, of vibrations at so high 
a pitch is hardly feasible. 
I may perhaps be asked if a characteristic s, 
having a dominant pitch, is not a pure tone, what 
is it? I am disposed to think that the vibration 
is irregular. A fairly defined pitch does not 
necessitate regular sequences of more than a few 
(say 3-10) vibrations. What is the state of 
affairs in an organ-pipe which does not speak 
well, or in a violin string badly bowed? An 
example more amenable to observation is 
afforded by the procession of drops into which 
a liquid jet breaks up. If the jet is well pro- 
tected from outside influences, the procession is 
irregular, and yet there is a dominant interval 
between consecutive drops, giving rise under 
suitable conditions to a sound having a dominant 
pitch. Vibrations of this sort deserve more 
attention than they have received. In the case 
of the s the pitch is so high that there would be 
NO. 2389, VOL. 95| 
but without modifying the above 
NATURE 


[AUGUST 12, 1915 

opportunity for interruption so frequent that they 
would not be separately audible, and yet not so 
many as to preclude a fairly defined dominant 
pitch. I have an impression, too, that the s in- 
cludes subordinate components decidedly graver 
than the dominant pitch. 
Similar questions naturally arise over the char- 
acter of the sh, f, and th sounds. 
RAYLEIGH. 

GAUGES. 
NTERCHANGEABILITY forms the basis of 
manufacture wherever there are a large 
number of articles to be made, and the processes 
required in order to secure it are well understood. 
The system makes it possible to subdivide the 
manufacture of any part into many small pro- 
cesses, each effected by one worker, aided by 
machine or hand tools, who acquires great skill 
in his particular operation. The parts so made 
must be capable of being assembled with the 
minimum labour; in fact, assembling ought to 
consist merely of putting together parts selected 
at random from stocks of details, with the cer- 
tainty that these will fit without any additional 
tool work on the part of the assembler. Each 
operation performed in the making of any part 
must give to that part definite dimensions within 
prearranged limits. The precise dimensions and 
limits are chosen with a view to securing running, 
push, driving, or shrinking fits, according as will 
be required in the assembling operations. Gauges 
by means of which the results of each operation 
may be tested thus become a necessity in the 
manufacture of interchangeable parts. These 
gauges are generally of the limit form. Very 
large numbers of these gauges are required in 
the production of munitions. 
Suppose the operation to consist of boring a 
hole nominally 1 in. in diameter, and that the 
finished hole must not exceed 1°003, nor be less 
than 0’997 in. in diameter. The gauge employed 
would be cylindrical, having one end 1°003, and 
the other end 0°997 in. in diameter. If the smaller 
end can go into the hole, the hole is not less 
than 0'997 in. in diameter, and if the larger end 
cannot go in, the hole is not larger than 1°003 in. 
diameter. By use of a gauge of this kind, any 
workman of ordinary intelligence may produce 
work having a high degree of accuracy. 
It is obvious that the gauges employed must 
be much more accurate in dimensions than the 
work which they are employed to check. Thus 
the gauge mentioned above would have its larger 
end probably within the limits 10031 and 170029, 
the variation permitted being one ten-thousandth 
inch above or below the rated size. Further, 
gauges must be made of very hard material in 
order to reduce wear, and must have well-finished 
surfaces. The hard steel used for this purpose 
is often of such quality as to require annealing 
once or twice before the necessary machining 
operations can be completed. After machining 
nearly to the finished size, the gauge is hardened, 
a process which generally warps the material- 


