Evening star. [volume] (Washington, D.C.) 1854-1972, 1890-11-22
THE SECRET OF THE TELEPHONE

THE SECRET OF THE TELEPHONE
DR.. Woodman Explains Its Science
How Sound is Transmitted.
At the Catholic University yesterday after.
noon Rev. Clarence E. woodman, AM, Phi. d.
delivered the second lecture Of his public
course on Electricity in Modern Life" Hi
subject was "The Telephone" After explain
ing the electrical principles involved in the
theory Of the telephone he went on to speak OF
the acoustic ones.
SOUND AND SOUND WAVES.
Sound Is caused by air vibrations affecting
the nerves Of the ear. These move with GER
tain velocity, which has been accurately meas
ured and found to be 1.09S feet per second at q
temperature OF 30o Fahrenheit and 1,l25 feet
per second Mt co.. In water this speed is in
creased four fold, in steel sixteen fold and 30
on, according to the substance employed.
One who stands near o cannon while IL is
being fred will notice four things: First the
fash; second. the cloud Of smoke rushing from
the cannon's mouth; third, the trembling OF
the ground on which he stands and fourth, a
strong rush OF air reaching the ear at the Same
time with the sound This puff of air is the
sound wave. The air in front Of the cannon
is violently compressed and this center Of COM
preston begins to move outward in every di-
rection like the rlpples formed by a st one
thrown into still water. Each compression is
followed by its accompanying rarefaction, Just
as the little wave circles in water have their in
mediate valleys. If definite number Of such
COMBINATIONS and rarefactions occur in given
time the result is what we call tone For in
stance. tuning fork giving the middle G
vibrates 256 milos per second exactly. At the end
Of one second a wave started by this tuning
fork has travelled about l 100 feet; there must
then have been 256 sound waves, each about Az
feet long, II the fork gave 8 of the third
octave each wave would be one foot long.
Sound has three characteristics. That by
which it is high or low called pitch. This
depends entirely upon the number Of vibrations
per second. II one note has twice as many
vibrations per second as another, the first will
be exactly an octave higher than the second.
The intervals into which an octave is divided
stand on precise mathematical relations to each
other.
The second characteristic Is that by virtue Of
which sounds are loud or soft. This is called
intensity and depends entirely upon the ampli-
tude. height or size of the sound waves. with
out regard to their length or their number.
The third characteristic of sounds is THAI
most important one by which the sound pro-
duced by one instrument is different from tina;
produced by another, by which, for example,
we distinguish piano forte from violin
motto or recognize friends voice. This is
REPRODUCING VIBRATIONS.
1t is evident, the speaker said, that if by any
means We can produce vibrations whose curves
correspond to those of given tone or given
number OF tones the same impression will be
produced upon the ear as would have been
produced by the original tone, whether simple
or composite.
The first experiments in the production Of
musical sounds at distance were made in 1861
by Philip Refs of Friedrichsdorff, Germany.
The principle Of his apparatus was as follows:
Imagine an aperture made in the side of that
ordinary instrument of torture, boys toy
drum. II piece OF metal about the size Of q
ten-cent piece is glued to the center Of one of
the drum heads and a light spring is fastened
to the edge so that its point will just rest upon
the center piece it is evident that if musical
the membrane Of the drum head will set up a
vigorous hopping of the spring point. If mid
die G Is sounded the spring will hop up and
down upon the center piece 256 times per Sec
ond. Ii the spring and center piece be con-
nccted with a powerful battery and long
electro magnet it will be found Gas first dis
covered by Prof. Page of Salem, Mass. in 1887. }
that every time the current is broken there
will be faint click in the iron core OF the
magnet, owing to its sudden change of length
under magnetic influence. When G is sung
into the drum the clicks will be heard in the
the original note. This form of telephone can
only produce one OF the characteristics Of sound,
the pitch. Hence this form of telephone can
only produce musical sounds and is called 1.-The
singing telephone"
TRANSMITTING SPEECH.
1t remained for Mr.. Alexander Graham Bell
to discover method by which the intensity as
well as the pitch of tones could be electrically
transmitted, and thus the problem of trans
uniting audible speech was solved. The we'll
known reactions Of magnets upon electric cur
rents gave the clue. II the coil of this first
magnet be connected with similar coil on a
second identical magnet, situated at any rea-
sonable distance, the currents generated by the
vibrating armature in the first instance will
traverse the second coil, and there give rise to
fluctuations OF magnetic strength in the second
magnet, under the influence of which its arma-
ture will be more or less attracted according
to the number and amplitude Of the undula-
tlons.
This system of working the telephone, in
which the same instrument is used both for
transmitter and receiver, is system Of in
duced currents. By-and-by the minds of the
ingenious and scientifically inclined began to
think OF increasing the efficiency of the tele-
phone by using some other more powerful
source of these induced currents than the tele-
phone itself. The ''inductorium'' or Undue
ton COLI was already familiar piece OF ex-
perlmental apparatus and derived currents of
the most amazing strength had been produced
by 1t. The problem was to find some substance
whose electrical conductvity can be varied in
some way without being altogether broken by
the action of sound waves. Such n substance
was at last found in one Of the most common
Of all substances, that which is seen in a
smoky lamp chimney, on the bottom of fry
ing pam on the burnt end of match-the sub
stance variously known in it's various forms as
carbon, charcoal. SCOT and lamp black. piece
OF carbon, which IS a semi-conductor forming
part OF an electric circuit, varies its normal re-
sistance to q surprising degree under pressure.
AS the variation OF pressure can be given an
undulatory character by attaching the car bon
to diaphragm acting under the influence of
sonorous vibrations, the corresponding varia-
tions OF the intensity of the battery current of
which the carbon forms part, will be undula-
tory also. The lecturer described simple
form Of telephone which anybody can make
out OF two ordinary six-inch horseshoe mag
nets wood screw and some fine No. &c insu-
lated wire.
Badly Hurt by n Piece of Putty.
William A. Cheney, fifteen-year-old boy,
was brought to the Hahneman Hospital. in
Philadelphia, on Wednesday i'll an unconscious
condition. When he had been restored to con-
sciousness he said that some one had thrown q
piece of putty at him, striking him In the head
Matthias Wooley and William Soldering, two
bows who worked in the shop with Cheney