The Kenosha telegraph. [volume] (Kenosha, Wis.) 1860-1888, 1882-01-20
4 SOUND PHENOMENON.
| why Engine Bells and whistles Appear
| S0l1aefitiies to Vary in Pitch.
from the Providence Journsl.l


when two trains, going Ia al OBJ
posite direction at a rapid rate, meet
each other, with the engine bells ring
ing, or whistles blowing, a passenger OF
the one train notices marked variation
in the pitch Of the bell or whistle OF the
other train. When the sound first
strikes the ear, the pitch is at its highest.
Gradually it goes down as the train
dashes past, and the lowest pitch is
reached when the last notes fall On the
ear Why is this?"
This question was propounded to an
engineer by an individual thirsting for
| information.
1.-The question is simple enough,
was the reply. To start with, 1t is an
axiom which needs no proving that the
| pitch of sound depends on its number
Of vibrations. Thus, while forty vibra-
lions a second produce the lowest sound,
10000 second produce the highest.
Pitch rises with an increase Of the num-
Der of vibrations.
"a certain number of vibrations are
emitted by the bell or whistle during
the time the train is running certain
| distance-say quarter of mile. Sup
pose each train runs this distance IN half
8 minute. Then, as the one train ap-
| proaches that in which the listening
passenger is seated, all the vibrations
emitted during the half-minute will
strike the ear in less than half minute
(supposing, Of course, that they can be
heard over so great distance The
! reason for this Is that the first will not
be heard until more than two seconds
after it has been emitted, as the sound
will have to travel half mile, while the
last will be heard the instant it is emit.
ted, because the engine will then be
within a few feet of the ear. Thus,
thirty seconds vibrations will be heard
in twenty-eight seconds. When the
trains are receding from each other, the
vibrations emittedduring the half-minute
will take rather more than thirty-two
seconds to reach the ear, as that emitted
| when the train is half mile off will
nave to travel to the ear.
''Can you illustrate this to make it
plainer?' the engineer was asked.
Certainly can. Suppose man
! NlNA ~ 1uOUCA uOSO SIRIUS bC4i YbAoAs
from tub. The capacity Of his hose
enables him to squirt pint of water per
second into that tub. But if, during,
| say, five seconds, he walks up to the
tub, all the while allowing his hose to
pour water into it, there win be more
than five pints of water as the result OF
that five seconds work. There will be
| five pints, plus the quantity contained in
the stream which would have fallen to
the ground if he had stood still and at
the end Of the five seconds turned the
cock, shutting off the stream. By the
approach of the whistle or bell of an en-
| CINE greater number of vibrations
meet the ear in q given time, just as a
| greater quantity Of water reaches the
tub from the hose by the approach Of
the nozzle. And, accepting as correct
the axiom that the greater number Of
vibrations the higher the pitch, it will
be seen that when the trains approach
the ear gets more than its due share Of
vibrations per second, and when they
recede it gets less than its share.