The sun. [volume] (New York [N.Y.]) 1916-1920, 1919-08-10

are no longer necessary-the anti
noise telephone has made them obso-
lete. Now for the tale Of a war time
device-kept secret for many months
by order OF the Government-which Is
available to-day for public service for
the promotion of vocal intercourse
under circumstances hitherto well
nigh prohibitive. We owe this amaz-
ing departure to the originality Of two
men who had the inspiration to break
away from the conventional lines of
research and to blaze an entirely new
path in an opposite direction, SO to
speak.
When the United States Govern
ment decided to establish a high power
radiotelegraph station at the navy
yard, Mare Island. California, the sys-
tenn adopted was that developed by
Waldemar Poulsen. the Danish in
ventor of the we'll known flaming arc
transmitter. DIR. Poulsen sent to the
United States at that time a youthful
representative, Peter L. Jensen, who
had been associated with him In his
wireless researches. Subsequently
Mr.. Jensen met Edwin 8. Pridham. a
Californian and Stanford University
alumnus, who was also an electrical
engineer. Together these men worked
in putting up and in operating the
first American station to use the .Poul-
sen method. That comradeship led
them to collaborate in efforts to Inn
prove both wireless and telephone ap-
paratus. Finally, believing that much
So k.xr ALL ~
Pridham and Jensen went to Europe
in the latter part OF 1910. where they
met and discussed various problems
in autobiography with foreign pio-
iieers in the art.
A Loud Speaker Produced.
While there they discovered traces
OF research which they believed would
be well worth following; and in 1911
they returned to California full Of this
idea but with purses too much de-
pleted to enable them TO go very far
in purchasing the needful apparatus.
However, they happily interested a
local retired capitalist, Richard O'Con-
| nor, who furnished funds enough to
equip an experimental laboratory at
Napa, little north of San Pablo Bay.
II was there that they hit upon a
radically different type Of telephone
| receiver, which led a short time after
| ward to the production of a conspicu-
ously loud speaking instrument.
In the ordinary telephone the re-
ceiver consists of a thin, soft, iron
diaphragm. which Is vibrated or fiexed
by the arriving electrical impulses sent
over the circuit to a magnet lying Just
back of the disk. The movement OF
| the disk, responding to the electrical
waves induced at the distant end OF
the line by the transmitter. produces
| sound waves which the listeners ear
recognizes as speech. Pridham ami
Jensen broke away from this form of
receiver and developed instead one
which Is technically characterized as
"the saturated field. electro-dynamic
type" in which a fiat coil of wire IL
so placed that It will vibrate across the
path OF the operating lines OF magnetic
force much after the manner of a hair
spring. let us say, in the sweep on an
electric fans breath.
This coil is attached to bronze, not
an iron. G'aphragm, and the latter IL SC
affected that It reproduoes with Pc
culiar clearness and faithfulness every
impulse set up by the far away trans
mitter. Without going into techpical
niceties the consequence of this inven-
ton is an amplihcatiop|of the trans
mitted sound and thus came into being
the Magnavox, or loud speaking tele-
phone. This is only one phase of the
problem, however.
| While the loud speaking telephone
by itself makes it possible for tn,
listener TO hear when 1t might other.
wise be very difficult or out Of thu
| question for him to. do so, still q
phone conversation Is not a one sidet
affair, az all Of US know. The loud
speaking receiver Is good enough al
far as II goes, but the very noisei
which II overcomes locally must bs
kept out of the transmitter when the
listener starts to talk. For example
let us imagine that the telephone con.
nection Is between some on in tn,
peaceful atmosphere Of the suburbs
and a man in Manhattan whose offics
is next door TO a slyscraper in tn,
process Of erection. The rivet gun 4
creating q deafening din. but even 10
the loud speaking Fseeiyer nsutralizsi