The Sedalia weekly bazoo. [volume] (Sedalia, Mo.) 187?-1904, 1881-12-20
A SOUND PHENOMENON.
Why Engine Bells and Whistles
Appear to Vary in Pitch at
Times.
Pro,idsn" ,R. I. journal

Pr",idsn"' ,R. l. Journal
When Two trains, going In an opposite
direction, al a rapid rate. meet each other
with the engine bells ringing or whistles
blowing, passenger OF one OF the trains
notices d marked variation In the pitch 81
the bell ar whistle oil the other train
When The sound iirsl strikes The ear the
pitch is at lis highest. Gradually il goes
down a. ihe irain lssh.s past, and the
lowest pitch j, reached when III. last notes
TALL on the ear Why is this"
This question was propounded To an en-
gineer The other day by an individual
thir>,ing Tor information
The question l. simple enough" WAS
the reply. To start with, ii i AN axiom
which needs no proving that The pitch OF a
sound d-Iends upon It's number of vibra-
rions. Thus. while forty vibrations SET
Ond preduc. the lowest sound, $1,000 a
second produce the highest. Pitch rises
With an Increase OF the number OF yibra-
tions.
A certain number OF vibrations are
emitted bv the bell or whistle during the
time The train i running q certain dis
iance-say q quarter OF mile. suppose
each train runs this distance in half a
minute. Then, as the one train approaches
that in which the listening pas
senger il seated. all The vibrations
emitted during the hall minute will strike
the ear i'm less than half minute sup
posing, of course, that they can BE- heard
over so great a distance The reason of
this Is that the first will not be heard uutil
more than two seconds after IL has been
emitted, a. the sound will have 10 travel
half mile, while the last will be heard
the instant il is emitted, because the en-
gin. will then t'e within a few iect al the
ear. Thus, thirty seconds vibrations will
De- heard in twenty-eight seconds When
the train are receding from each other, the
vibrations emitted during the half minute
will take rather more than ihirty-iwo SEE
onds To reach the ear, a. thai emitted when
The train is hall mile of will have To
travel Ia the ear"
Tan Won illustrate this Io make il
plainer?' The engineer MAS asked.
Certainly can Suppose man with
a rubber Lose stand> ten wards from the
tub. The capacity oil his hose enables him
10 squirt pint OF water I.er second into
that inb. i5ui ii. during. saw i've seconds.
he walks up 10 the tub, all the while al
lowing his hose to pour water into ~. there
will To- NOR than five pini> of water as the
result oi that FIVE seconds work There
will tee live Pinls, pins the quaniit, CON
tanned Ia the stream which would have
fallen io the ground il he had stood still
and al the end az the i've seconds turned
the cock, shutting of the stream By the
approach "i the whistle or bell Of an en-
glib. Il greater number of vibrations meet
the cal ia a given time. just a. a greater
quantity al wafer reaches The ,uh from IA.
hose hy the approach oi the nozzle And
accepting correct the axiom n Il, the
greater nmmier "i vibrations the higher
lhr pitch, IL will IL seen that when the
trains approach the ear get NOR, than ii>
du- share 81 vibrations PER Second, and
when They r.rc'i- II y.I> i->> than IT.
share.