Full text of "Wireless telephony, in theory and practice"

This is a digital copy of a book that was preserved for generations on library shelves before it was carefully scanned by Google as part of a project
to make the world's books discoverable online.

It has survived long enough for the copyright to expire and the book to enter the public domain. A public domain book is one that was never subject
to copyright or whose legal copyright term has expired. Whether a book is in the public domain may vary country to country. Public domain books
are our gateways to the past, representing a wealth of history, culture and knowledge that's often difficult to discover.

Marks, notations and other marginalia present in the original volume will appear in this file - a reminder of this book's long journey from the
publisher to a library and finally to you.

Usage guidelines

Google is proud to partner with libraries to digitize public domain materials and make them widely accessible. Public domain books belong to the
public and we are merely their custodians. Nevertheless, this work is expensive, so in order to keep providing this resource, we have taken steps to
prevent abuse by commercial parties, including placing technical restrictions on automated querying.

We also ask that you:

+ Make non-commercial use of the files We designed Google Book Search for use by individuals, and we request that you use these files for
personal, non-commercial purposes.

+ Refrain from automated querying Do not send automated queries of any sort to Google's system: If you are conducting research on machine
translation, optical character recognition or other areas where access to a large amount of text is helpful, please contact us. We encourage the
use of public domain materials for these purposes and may be able to help.

+ Maintain attribution The Google "watermark" you see on each file is essential for informing people about this project and helping them find
additional materials through Google Book Search. Please do not remove it.

+ Keep it legal Whatever your use, remember that you are responsible for ensuring that what you are doing is legal. Do not assume that just
because we believe a book is in the public domain for users in the United States, that the work is also in the public domain for users in other
countries. Whether a book is still in copyright varies from country to country, and we can't offer guidance on whether any specific use of
any specific book is allowed. Please do not assume that a book's appearance in Google Book Search means it can be used in any manner
anywhere in the world. Copyright infringement liability can be quite severe.

About Google Book Search

Google's mission is to organize the world's information and to make it universally accessible and useful. Google Book Search helps readers
discover the world's books while helping authors and publishers reach new audiences. You can search through the full text of this book on the web

at |http : //books . google . com/

j fiTftitt w ■I'iiiJiitieMUtJtwihTtgjg

TT TIf I IH flTi TTTT iffiflfMlrt fiT ITIirtT gfi ''°-'*^-^°''^ir?B Ti' Iff iffji.

REESE LIBRARY

OF TtlK

UNIVERSITY OF CALIFORNIA.

Class

irap^Fa gT Wr-hr-tf^-yTr-T

'. 'M JM. .V. -:h- 'kf H.i.y < .w." .H.' <

r- y - wn r^S^ j i y

The D* Van Nostrand Company

inlend this book to be sold to the Public
at the advertised price, mA supply it to
the Trade on terms which will not allow
of reditctioo.

WIRELESS TELEPHONY.

Wireless Telephony

3n ^beori? an& practice

ERNST RUHMER

I 4

TRANSLATED FROM THE GERMAN

JAMES ERSKINE-MURRAY, D.Sc.

FELLOW OP THB ROYAL SOCIETY OP EDINBURGH
MEMBER OP THB INSTITUTION OP ELECTRICAL ENGINEERS

Mitb an appendi; bi? tbe Utanslatot

AND NUMEROUS ILLUSTRATIONS

NEW YORK
D. VAN NOSTRAND COMPANY

23 MURRAY AND 2^ WARRBN STREETS

LONDON
CROSBY LOCKWOOD AND SON

1908

\x^

^^.s>

^^^

AUTHOR'S PREFACE.

T^HE friendly reception given by both the home
and foreign technical press to my little book,
**On Selenium and its Importance in Electro-
technics," which appeared in the end of 1902, has
encouraged me to make known to wider circles the
researches and experiments which have been made
in Wireless Telephony up to the present.

In order to render the presentation of the subject
complete, notice has been taken of Light-Telephony,
and of the fundamental physical phenomena on which
it is based, especially in regard to its bearing on
more recent work.

The greater part of the second section is devoted
to a description of Electric Wave Telephony, the
recent advances of which are of the greatest promise,
and will on this account be of far-reaching interest.

In accordance with the frequently expressed
wishes of my friends, a large number of references

196522

WIRELESS TELEPHONY.

Wireless Telephony

3n ^beori? anD practice

ERNST RUHMER

I 4

TRANSLATED FROM THE GERMAN

JAMES ERSKINE-MURRAY, D.Sc.

FELLOW OP THB ROYAL SOCIETY OP EDINBURGH
MEMBER OP THB INSTITUTION OP ELECTRICAL ENGINEERS

Mitb an Sppendis bs tbe Utanslatot

AND NUMEROUS ILLUSTRATIONS

^^I^^^JUV^T/,^

^tTLTJJ^^

NEW YORK
D. VAN NOSTRAND COMPANY

23 MURRAY AND 2^ WARRBN STREETS

LONDON
CROSBY LOCKWOOD AND SON

1908

CONTENTS.

PART I.

WIRELESS TELEPHONY BY MEANS OF LIGHT
OR HEAT RADIATIONS (RADIOPHONY).

CHAPTER I.
The Photophone ----- 3

I'AGB

CHAPTER 11.
Varying Sources of Radiation - - - 14

CHAPTER in.
The Speaking Arc - - 20

CHAPTER IV.
The Photographophone - - - 36

CHAPTER V.
Light-Telephony at Useful Distances - 43

CHAPTER VI.
Best Working Conditions for Light-Telephony - 72

xii CONTENTS.

PART II.

WIRELESS TELEPHONY BY MEANS OF
ELECTRICAL FORCES.

CHAPTER VII.
Closed Circuit Telephony - - - - 79

PACiE

CHAPTER VIII.
Electromagnetic Induciion Telephony - - 88

CHAPTER IX.
Spark Telephony - - - 96

CHAPTER X.
Accelerated Spark Rates - - - 107

CHAPTER XI.
Multiphase Spark Discharges * - - - 118

CHAPTER XII.
High Frequency Alternators- - - - 131

CHAPTER XIII.
The Arc as High Frequency Generator - - 142

CHAPTER XIV.
The Poulsen Generator - - - - 154

CONTENTS. Xlll

CHAPTER XV.

PACK

Multiple Arcs in Air - - - - 159

CHAPTER XVI.

Applications of the Arc to Telephony - - 166

CHAPTER XVn.

The Duddell Phenomenon - - - - 174

CHAPTER XVHI.

Forced Vibrations . - - . . 183

CHAPTER XIX.

Conclusion - - - - - - 196

APPENDIX— Recent Advances - - - 198

BIBLIOGRAPHY 215

INDEX OF NAMES - - - - - 219

INDEX OF SUBJECTS ... 221

WIRELESS TELEPHONY.

INTRODUCTION,

The term "Wireless Telephony" means, in general, the
transmission of human speech to great distances without
the use of a connecting wire between the sending and
receiving stations.

In the simplest case the air serves as carrier of the
sound waves, while the voice of the speaker is the trans-
mitter, and the ear of the hearer the receiver.

This kind of transmission is so usual to us that we are
hardly accustomed to look upon it as wireless telephony,
although, with this simplest of all systems, particularly
when aided by such well-known instruments as the speak-
ing trumpet, much greater distances have been bridged
than by many more complicated methods.* How astonish-
ingly well the ordinary method may work under certain
conditions is shown by the "whispering galleries" in
churches, and by similar phenomena. Still better results
may be obtained by employing the air as a transmitter
of sound waves if we use as sender and receiver instruments
which magnify, by electrical means, the volume of sound
transmitted and received.

By using parabolic mirrors of 90 cm. aperture, in the
focus of one of which a loud-speaking telephone acted as
sender, while a sensitive microphone, connected in usual

♦ See " Short's Gouraudphon," Mechaniker^ viii., p. 261, 1900, and
ix., p. 79i 1901.

2 WIRELESS TELEPHONY.

fashion with battery and telephone, served the purpose of
receiver in the other, the author has obtained satisfactory
results in calm air at distances of over 1,500 metres.

Attempts have also been made to utilise the conductivity
of solids and liquids for sound, of which we may mention
the use of water as the medium of propagation by Trow-
bridge, and its many practical applications to submarine
signalling (Elisha Gray and A. J. Munday).

The methods by which speech may be transmitted by
means of light and heat radiation3 are much more compli-
cated ; they may be called

Radiophony.

The thermophone. Bell's photophone, and light tele-
phony, with which we shall presently deal, belong to
this class.

We are, however, accustomed to think of wireless trans-
mission as a purely electrical action.

The remarkable strides which have been made in the
knowledge of magneto-electric and electro-magnetic pheno-
mena have opened up to us many ways by which speech
may be transmitted through the ether without the assistance
of acoustical or optical aids.

Wireless Telephony by means of Electrical
Forces.

One can distinguish in this connection, as in wireless
telegraphy, between various groups of methods, such as —

1. Hydro-Telephony, in which the transmission takes
I place by means of electric currents through the earth or sea.

2. Induction - Telephony, which employs electro-
magnetic induction.

3. Wave-Telephony, in which electrical waves serve
to carry the speech as light waves do in light-telephony.

Let us now turn to the consideration of the individual
systems.

PART I.

WIRELESS TELEPHONY BY MEANS OF
LIGHT OR HEAT RADIATIONS.

CHAPTER I.

THE PHOTOPHONE.

The methods belonging to this group depend on the
alteration of the intensity of the light or heat radiations
sent out by the transmitting station (Photophony or
Thermophony). These variations of intensity are again
converted into sound waves at the receiving station. The
conversion may be effected electrically by utilisation of
the sensibility of selenium to light — a discovery made by
May, one of Willoughby-Smith*s assistants. The element
selenium, which belongs to the sulphur group, exists in
several modifications, but of these only the crystalline,
which may be obtained from the others by heating or
melting, is a conductor of electricity, and possesses the
peculiarity that its conductivity varies with the illumination.
In proper circumstances this form of selenium conducts the
electric current many times better when illuminated than
when in the dark.

The Linkage of Light and Electricity.— Smith de-
scribed this discovery of May's very graphically in a letter
of 1 2th February 1873 to Latimer Clark, at that time
President of the English Institution of Telegraph Engineers,
in which he said : —

4 WIRELESS TELEPHONY.

" With the assistance of the microphone one can hear
the footsteps of a fly as loudly as if it were the trampling
of a horse on a wooden bridge, but it strikes me as much
more wonderful that by means of a telephone I can hear
a ray of light falling on a metal plate."

On account of the high resistance of the preparation of
selenium, and hence the difficulty of experimenting, and
also in order to take the greatest possible advantage of
the influence of the light, the so-called selenium cell de-
scribed by Werner Siemens in 1875 is used. We shall
not go into the details of its construction here.*

The Photophone. — Bell, the ingenious inventor of the
telephone, was the first who achieved, after much study of
the remarkable behaviour of selenium under the influence
of light, and many laborious researches, the production of
useful selenium cells, and, in common with Sumner Tainter,
made the first practical application of the sensibility of
selenium to light in combination with his telephone, by
constructing a photophonic receiver (1878).!

The flat selenium cells made by Bell for this purpose
consisted of two copper or brass plates, in which a large
number of holes were bored, and which were separated by
an insulating plate of mica. In the holes in one plate
were fixed conical brass studs which entered the holes in
the other plate, but without touching the plate itself.

The annular spaces surrounding the studs were filled
in with melted, black, glassy selenium, and the cell heated
over a gas flame until the selenium began to melt and turn
into the slate-coloured crystalline modification.

Bell and Tainter also constructed cylindrical cells for
use in parabolic mirrors out of a series of brass and mica
discs piled alternately on one another. As the mica discs

* For further descriptions see Ernst Ruhmer, "Das Selen," Berlin,
1902, and E.T.Z., 25, pp. 102 1- 1030, 1904, Lecture before the Elektro-
technischen Verein, 22nd March 1904.

+ See Alexander Graham Bell, " The Photophone."

THE PHOTOPHONE.

were cut of less diameter
than the brass, there re-
mained, beyond their
edges, a number of ring-
shaped notches into which
the melted selenium was
run. Each ring of selen-
ium was thus in contact
with two neighbouring
brass plates. In order to
keep the resistance as
low as possible, all the
even numbered brass
plates were connected to
one terminal of the cell,
and all the odd to the
other. Thus the selenium
rings were all in parallel,
and after their conversion
into the grey modifica-
tion, the cell offered a
comparatively small re-
sistance to the electric
current.

While in the case of
the flat cell, described
above, the portion of the
surface actually exposed
to the action of light was
only about o.ii of the
whole, in this newer form
the ratio was as much
as O.6.

The resistance of
Bell's cell was approxi-
mately 1,200 ohms when in darkness, and 600
illuminated.

'J CL^

:g.

ohms when

6 WIRELESS TELEPHONY.

In order to reproduce the words spoken at the sending
station by means of this type of cell in connection with a
telephone, it was necessary to construct a transmitting
apparatus which should be influenced by the waves of
sound so that a ray of light directed by it on to the receiver
should be made to vibrate synchronously with these waves.

Bell and Tainter have given nearly fifty different methods
by which a beam of light may be thus controlled.

These methods may be divided into two groups. In
one of these a source of light of constant intensity is em-
ployed, and the ray of light from it is modified at some

Fig. 2.
Photophonic Transmitter with Condensing Lens.

point on its way ; in the other group a source of light is
used in which the intensity is altered directly by the sound
waves.

In the original photophone, which belonged to the first
group, the rays of the sun were reflected by a mirror on to
a silvered glass or mica membrane placed over a conical
mouthpiece, and thence to the receiving station (Fig. i).
Since the membrane, when set in motion by the sound
waves, became alternately concave and convex, the parallel
rays of sunshine became alternately convergent and diver-
gent, and thus fell upon the reflector at the receiving

THE PHOTOPHONE.

station with rapidly varying intensity. These rays are
concentrated at the focus of the reflector, on the selenium

Figs. 3 and 4.
Photophonic Transmitting and Receiving.

cell, and, if the latter be connected in series with a battery
and telephone, are reconverted into sound waves.

WIRELESS TELEPHONY.

Another arrangement, used by Bell in his experiments
(Fig. 2\ differs only from that shown in Fig. i in the
addition of two lenses ; the upper one, ^, serves to concen-
trate the light on the reflecting membrane, while the lower
one, Lg, renders it again parallel. Figs. 3 and 4 show the
sending and receiving stations in action.

With this apparatus Bell and Tainter made a great
number of experiments in which the sender and receiver
were so far apart that the sound could not be heard directly
through the air.

Fig. 5.
Arc Lamp as Source of Light.

In one of these experiments (1880) Tainter was at the
sending station, which was placed on the tower of the
Franklin College at Washington, while the receiver was in
Bell's laboratory window in 1325 L Street; the distance
being 213 metres. As Bell put the telephone of the receiver
to his ear he heard clearly the words, "Mr Bell, if you can
understand what I am saying, come to the window and
wave your hat." The transmission of speech by means of
light rays was thus perfect at this short distance.

Instead of the sun's rays the light of an arc lamp,
rendered parallel by means of a mirror or lens, may of
course be used (Fig. 5).

THE PHOTOPHONE.

To the same group of transmitters belong the methods
in which the ray of h'ght is influenced by a lens with a
variable focal length, or in which it is polarised and then
altered in the ways discovered by Faraday and Kerr.

In Fig. 6 an arrangement of this kind is shown. The
microphone M is in series with the battery B and the coil S.
The light rays from the source L are rendered parallel by
a lens and polarised by the NicoFs prism P^. After travers-
ing the bobbin the light is extinguished by a second

crossed Nicol at P,.
duced in the coil by
speaking ^tp the
microphone M^ the
plane of polarisation
will %e more or less
turned, and thus a
greater or less
amount of light will
pass out through Pg,

If oscillating currents are now pro-

and in this
vibrations
membrane
microphone

way the
of the
of the
may be

llKiH

J9 fi

Fig. 6.
Polarised Light Transmitter controlled by Electro-
magnetic Action on Plane of Polarisation.

converted into altera-
tions of the intensity
of light.

In order to strengthen the action an iron core may be
introduced into the coil having a hole bored along its
axis. In this is placed a piece of transparent heavy glass
which possesses a large magneto-optic constant. This
method differs from the above-described system in that
it is possible to arrange that practically no light passes out
to the receiving station when the apparatus is at rest.

There are many other ingenious methods belonging to
the first group, which might be described here, but which
we shall, however, pass over as they do not introduce any
new principle of importance in wireless telephony.

WIRELESS TELEPHONY.

Before we go on to the methods of the second group,
which employ a source of light whose intensity varies with
the sound waves, we shall describe shortly an arrangement
of Bell's in which the transmission is by means of the heat
waves which accompany the light.

Bell's Thermophone. — On the occasion of the exhibi-
tion at Chicago in 1893, ^^^ showed a thermophonic
apparatus of this type for the transmission of speech
(Figs. 7.9).

The transmitter is, as in the photophone, a thin silvered

Fig. 7-
Photophonic Transmitter.

mirror against a mouthpiece, which reflects the light of
an arc lamp.

The receiver (Fig. 9) consists of a small glass bulb,
containing a little blackened (charred) piece of cork. From
the bulb rubber tubes are carried to the ears of the observer.
The cork ball is placed in the focus of the parabolic mirror
of the receiver. The variations in the intensity of the heat
radiations cause, as Bell has shown, corresponding altera-
tions in the volume of the cork, and therefore in the
surrounding air, which of course travel through the tubes
as sound waves.

THE PHOTQPHONE.

1 1

Mercadier's radiophone is almost identical with this
arrangement of Bell's, differing from it only slightly as to
the construction of the thermophonic receiver. This latter

A/tc La*f^

Letu

Fig. 8.
Tbermotelephone.

consists of a glass tube with thin walls, closed at one end
and containing a plate of mica covered with lampblack.

Fig. 9.
Thermophonic Tube.

=®

To the open end of the tube rubber connecting tubes are
attached as before.

The mica gives out sound waves corresponding to the
variations of intensity of the light from the transmitter
just as in Bell's form.

WIRELESS TELEPHONY.

Another thermophonic receiver, in which the reception
is telephonic, is shown in Fig. lO. It consists of a thin-
walled hollow sphere of iron B, forming one pole of a
magnet D, on which is a coil of wire in series with the
telephone E. The undulating rays of heat, striking on the
pole B, cause corresponding variations in the strength of
the magnet, and hence produce induction currents in the
coil C which are audible in the telephone. A similar result
may be obtained by means of a thermopile.

\ A

Fig. io.
Thermophone in Use.

The loudness of the thermophone is as a rule much
less than that of the photophone, in which a selenium cell^
is used ; the simple thermophonic receivers which we have
described standing in something of the same relation to
the selenium cell as a telephonic transmitter does to the
microphone, />., the first converts the energy actually trans-
mitted into sound waves, while the latter merely controls
a new source of power.

The apparatus of Bell's which we have described above
was found capable, at the Chicago Exhibition, of trans-
mitting speech to a distance of about lOO metres. We
may here remark that Tainter, being struck with the
extraordinary sensibility of blackened surfaces, attempted

UNIVERSITY

"^ THE PHOTOPHONE.

to substitute soot for selenium in the selenium cell. One
of these receivers, a so-called soot cell, was then connected
in series with a telephone and battery as in the case of
a selenium cell. It is not known whether practical results
were obtained with this altered form of thermophonic
receiver.

CHAPTER II.

VARYING SOURCES OF RADIATION.

Varsring Source of Light. — Let us now turn to the
second class of radiophonic transmitters, which employ a
source of light which varies with the sound waves. The
simplest example of this kind is one in which a Konig's
manometric flame is used.

Fig. II.
Jamieson's Transmission by Manometric Flame.

It is not certain to whom the credit of having first used
such a flame for radiophonic purposes should be awarded.
It is very probable that Bell's photophonic experiments
may have suggested the same idea to several minds at once.

Apparently one of the first publications was made by
Andrew Jamieson, of Glasgow {Nature^ lo, ii, 1881), from
whose description J. W. Giltay in Delft constructed the

SOURCES OF RADIATION.

photophone shown in Fig. ii. This consisted of a mano-
metric capsule A as transmitter and a selenium cell B as
receiver. Since the little 1.5 cm. high
flame did not give off sufficient light,
Giltay improved it by drawing it through
a wash-bottle containing gasoline (Fig.
12). If one speaks into the mouthpiece
the membrane in the manometric cap-
sule vibrates, the gas in the capsule is
compressed or rarified in accordance
with the sound waves, which causes the
flame to rise and fall with a rapidity
too great to be detected by the naked
eye. These alterations of the intensity
of illumination act on the selenium cell,
and give in the telephone connected to it a perfect repro-
duction of the original voice.

In order to show that the transmission is really due to

Fig. 12.
Gasoline Bottle.

Fig. 13.
Varying-flame Photophone.

the action of the light on the selenium cell one may intro-
duce a piece of tin or other opaque material between the
flame and the cell, and notice that the reproduction of the
speech entirely ceases.

l6 WIRELESS TELEPHONY.

Fig. 13 shows a similar radiophonic apparatus with a
thermopile as receiver.

Giltay and the author afterwards employed acetylene
gas instead of ordinary gas in order to obtain a flame
richer in carbon.

Fig. 14 shows Giltay's original apparatus, which has,
however, been recently improved by use of three acetylene
flames in place of one (Fig. 15). The acetylene gas was
made in a small producer </, like those which are used in

rf;

1 1

•^

mMm H

■

L-Sb

4l^^jVvx

'^^AM

Fig. 14.
Giltay's Acetylene Flame Photophone.

cycle lamps, the water supply to the producer being regu-
lated so that the flame, or flames, maintained a height of
about LS cm. The manometric capsule was so placed that
the flame was about i cm. from the selenium cell.

Fig. 16 shows an apparatus constructed for use in
schools and colleges. In this apparatus the flat selenium
cell is illuminated both directly by the acetylene flame and
by reflection from the spherical mirror placed behind it
The selenium cell is connected, by means of the terminals

SOURCES OF RADIATION. 1/

on the lower board, with a small battery of dry cells or
accumulators in series with a pair of telephones.

Of course if the two experimenters are close together,
it is impossible to distinguish whether the transmission is
direct or through the apparatus ; it is best, therefore, to
provide a long connecting wire to the telephone so that the
latter may be taken into an adjoining room where the voice
of the speaker is not distinctly audible.

Fig. 15.
Triple Burner Transmitter.

In order to adapt this apparatus to wireless telephony
over short distances the selenium cell may be taken out of
its holder, and a parabolic mirror substituted for it. This
apparatus now becomes a transmitter, as shown in Fig. 17.
The light of the acetylene flame is thrown by the mirror
on to the receiver, which is fitted with a lens or mirror to
concentrate the rays on the selenium cell, which has now
been removed to some little distance and connected, as

WIRELESS TELEPHONY.

Fig. i6.

Fig. 17.
Experimental Photophones.

SOURCES OF RADIATION. I9

before, to a battery and telephone. Speech may thus be
transmitted across a lecture room. (See Figs. 18 and 19.)

In place of speaking directly into the manometric cap-
sule one may arrange this telephonically, as was first done
by Giltay (Fig. 20).

In order to bridge over greater distances a more power-
ful, and at the same time more concentrated, source of light
than a gas flame is required. Obviously the electric arc
would be extremely suitable since its rays may be directed
in a beam of great intensity by means of a reflector. At
the time of Bell's photophone experiments, however, no
way was known by which the intensity of the arc could be
influenced by the vibrations of speech.

Since the attempt to transmit human speech to a
distance by means of a ray of light in these radiophonic ex-
periments had attained so little practical success, they soon
fell — in spite of the ingenuity of BelFs telephone, which
pursued its conquering course throughout the entire
world and is now a necessary adjunct of modern civilisa-
tion — into the realms of oblivion.

CHAPTER III.

THE SPEAKING ARC,

Discovery of the Speaking Arc. — The discovery of the
speaking arc by Simon in 1898 introduced new possibilities
in the development of this method of wireless telephony.
It is interesting in this connection to recall a paragraph
(quoted by Giltay, Mechaniker, xi., p. 31, 1903) in the
journal Engineering of 5th November 1880, in which the
principle of the speaking arc and of its application to light-
telephony was perfectly clearly given. The paragraph
read : " It would be highly interesting if future research
should lead to the discovery of a means of varying the
intensity of the electric arc proportionately to the sonorous
vibrations constituting articulate speech, so that a telephone,
in circuit with a photopile exposed to its rays, would repro-
duce the sound by which the light was in the first instance
thrown into vibration." ^

Let us turn now to the astonishing discovery of the
talking arc, made by Simon at the Physical Institute of
the University of Erlangen in the end of 1897 — the dis-
covery that an electric arc may be made to serve as a
telephonic receiver. He observed that the arc of a con-
tinuous current lamp gives out a loud rattling noise if its
leads run near a circuit in which a rapidly interrupted
current is flowing. The latter may be produced by means
of a few secondary cells connected to the interrupter of an
induction coil. The oscillatory secondary currents induced
in the leads of the arc lamp superpose themselves on the
continuous current and produce the remarkable acoustic

THE SPEAKING ARC.

phenomena. Since the action was produced by extremely
small induced currents, Simon tried to cause the arc to

speak by utilising the small alternating currents produced
by a microphone when it is spoken into. The arrangement
used is shown in Fig. 21.

WIRELESS TELEPHONY.

In order to intensify the effect the secondary winding
of a transformer was introduced into the lamp circuit, while

the primary winding conducted
the oscillating currents from the
microphone. The wonderful re-
sult was obtained that the arc
would transmit whistling, clap-
ping, singing, or music perfectly,
and that even words spoken into
the microphone were clearly
repeated. The effects produced,
however, were comparatively
weak. Later on, as the result
of experiments, it was found
possible to make the action
Fig. 19.— Selenium Cell wiih much more powerful, SO that

the whistling or talking of the

Mirror Condenser.

KiG. 20.
Gi.tay*s Transmiiter with Flame controlled by Telephone Diaphragm.

arc could be perfectly heard throughout a large hall.
The striking experiment has since been frequently re-
peated.

THE SPEAKING ARC.

We shall now describe shortly one or two other arrange-
ments. The author has considerably simplified Simon's
apparatus in the following way.* Since the correct design
of the transformer is dependent on conditions which are

MUftoffhans^ BattefUf

Fig. 21.
The Speaking Arc with Inductive Series-Control.

not constant, the use of one is entirely avoided, and an
electric coupling takes the place of magnetic induction.
The microphone circuit, which contains a considerable
resistance, is put in parallel with the arc, so that a separate
battery is not necessary (Fig. 22).

Fig. 22.
The Speaking Arc with Conductive Shunt-Control.

In place of the resistance one may ir\troduce a number
of cells, accumulators for instance, in the circuit, so that
there is only a difference of a few volts left to drive the

* See Mechaniker^ viii., p. 279, 1900.

WIRELESS TELEPHONY.

microphone. Finally, in order to conduct the oscillating
currents from the microphone entirely through the arc,
and prevent them from spreading themselves over the

leads, choking coils
of considerable in-
ductance are put in
the circuit, which
allow the continuous
current to pass freely,
but offer a very great
resistance to the
varying currents of
the microphone.
These latter, there-
fore, are almost en-
tirely retained in the
arc itself.

In place of put-
ting the microphone
in parallel with the
arc it may have its terminals connected to two points on the
supply leads, between which a resistance which gives a drop

\^aAlaMc ReMta^u^

The Arc with Conductive Series- Control.

Micftapkone

Fig. 24.
The Speaking Arc with Inductive Shunt-Control.

of from 4 to 6 volts is inserted (Fig. 23). In order that the
microphone current should go through the arc the common
part of their circuits must have a certain inductance. This

THE SPEAKING ARC. 2$

arrangement was described and used simultaneously, but
independently, by Simon and the author.

Duddeirs Arc. — Another arrangement, due to Duddell,*
in which an inductive coupling is used, is shown diagram-
matically in Fig. 24. In this also the microphone is in
parallel with the arc, its circuit being connected inductively.
The primary of a transformer is placed in series with the
microphone and battery, while the secondary, which con-
tains the same number of turns, has one end connected
directly to one terminal of the arc, and the other to the
other terminal through a condenser of from 3 to 5
microfarads. The condenser prevents the continuous
current of the arc from passing through the transformer,
while permitting the induced alternating current from the
microphone to pass freely. For the same reason two coils
of high inductance are placed in the arc lamp leads if
the supply be from an accumulator or from a supply net-
work. If a dynamo is used solely for the purpose of supply-
ing current to the apparatus, and has no inductionless
circuits, such as glow lamps, connected to it, these choking
coils are unnecessary, as the machine itself possesses
sufficient inductance. In the same way we find that the
microphone currents are throttled and weakened by the
inductance of the machine in the arrangements illustrated
by Figs. 21 and 23. A condenser connected in parallel
on the terminals of the dynamo partially obviates this
difficulty.

Microphone in Field Magnet Circuit. — Finally there
is an arrangement belonging to this class in which the
microphone current influences the field magnets of the
dynamo (Fig. 25). In this arrangement the electromotive
force of the dynamo varies exactly in accordance with the

♦ VV. Duddell, TAe Electricuxn^ xlvi., Nos. 8 and*9, 1900, and
Phys, Zeitschr.^ ii., pp. 425, 440, 1901.

WIRELESS TELEPHONY.

variations of the microphone current, so that the arc lamp
supplied by the dynamo repeats whatever is spoken into
the microphone attached to the dynamo. Simon used this
apparatus at Frankfort-am-Maine, where he gave an " Arc
Lamp Concert."

FleUMa^net thoki^Coil

Dunamc

Fig. 25.
Speaking Arc with Field Magnets ot Dynamo controlled by Microphone.

Theory of Talking Arc. — The theory of this remark-
able phenomenon is that the variations of the microphone
current cause corresponding variations in the amount of
heat produced, according to Joule's law, in the arc; and
these in their turn cause similar periodic changes in the
volume of the gases through which the arc is conducted.
The arc, therefore, generates sound waves.

In order to make the arc speak as loudly as possible, it
is necessary that the oscillations imposed by the micro-
phone on the constant current should be of as great ampli-
tude as can be obtained.

THE SPEAKING ARC. 27

Next in importance to the sensibility of the microphone
comes the proper design of the transformer.

F. Braun* has shown, further, that the action should be
greater while the arc current is increasing than under other
circumstances, a suggestion which is confirmed in actual
work.

Finally, it is advantageous to use as long an arc as
possible, for which reason soft-cored carbons, or still better,
carbons impregnated with salts, may be employed. With
high voltage (say 160 volts across the arc) and currents
of from 10 to 20 amperes arcs of between 5 and 7 cm. in
length may be obtained.

Figs. 26 and 27 show a complete apparatus, constructed
by Max Levy of Berlin from data supplied by the author,
for the repetition of this interesting experiment. The
transmitter consists of a Berliner granular microphone such
as is generally used in the Imperial Post Office telephones,
which is connected to the switch gear shown in Fig. 27.
A hand-regulated arc lamp serves as receiver, which is fitted
with a screen to prevent the eyes being dazzled by the
light.

We may here shortly consider how the speaking arc
may be made to perform the inverse function, />., to act as
a microphone.t In this case the sound waves cause altera-
tions in the volume of the arc, and so produce oscillations
of the current in its drcuit. In Fig. 28 an arrangement for
this purpose is shown, which Simon used in an experi-
mental lecture before the Electrotechnical Society of Berlin
on the 23rd of April 1901. J The arc is placed in the para-
bolic cavity H in the block B, the funnel T serving to
concentrate the waves of sound.

From the above explanation of the speaking arc it will
be seen that the temperature of the arc itself is subject to

* F. Braun, Wied, Ann., Ixv., p. 358, 1898.
t E.T.Z. Rundschau, xix., p. 321, 1898.
X E,TZ., xxii., p. 510, 1901.

WIRELESS TELEPHONY.

rapid oscillations. But, according to the laws of radiation
which have been so thoroughly worked out by modern
physicists, every alteration of temperature causes a corre-
sponding alteration in the intensity of the radiation. If,
therefore, the temperature of the speaking arc oscillates^

Fig. 26.
Speaking Arc Apparatus.

the radiation given out by it must oscillate in like
manner.

The speaking arc thus belongs to the second group of
photophonic transmitters, and fulfils its purpose as perfectly
as can be desired, since by means of a parabolic mirror the

THE SPEAKING ARC.

full power of the undulating rays of light may be directed
towards the receiving station.

Fir.. 27.
Regulator for Speaking Arc.

We shall consider later the most favourable conditions
for the action of the arc as a
photophonic transmitter, since
these conditions differ in several
essential points from those
which give the best acoustic
effects.*

As receiving apparatus for
the conversion of the light os-
cillations into waves of sound,
the photophonic instrument on
Beirs principle, which we have
described above, may be employed. A complete set of

♦ The author gave the essential points of difference for the first
time on 19th February 1901. Phys. Zeitschr.^ ii., p. 339, 1901.

Fig. 28.

The Arc as Converter of Sound into

Electrical Vibrations.

WIRELESS TELEPHONY.

apparatus df this kind for Light- Telephony, as we shall
call this type of photophony, is shown diagrammatically
in Fig. 29.

Let us next deal with the transmitter. The oscillating
current of the microphone is superposed, by means of a
transformer or otherwise, on the supply current to the lamp,
causing like variations in the amount of light radiated.
These undulating light rays are rendered parallel by a
parabolic mirror, and thrown on to the concave mirror at
the receiving station. There they are concentrated on a
selenium cell, thus causing the battery current to vary in

B Fig 29

My Mirrors ; ^, Arc ; 7", Transformer ; C, Microphone ; /?, Batter)' ;
Sy Selenium Cell ; R^ Telephone Receiver.

like manner, so that articulate speech may be reproduced
in the telephone by means of light.

It appears that Bell was the first to use the speaking
arc as a photophonic transmitter.* In collaboration with
H. V. Hayes in 1899, that is to say, very shortly after the
discovery of the speaking arc, he showed the transmission
of speech by means of an arc connected with a microphone
and placed in a large parabolic mirror at the exhibition of
electrical novelties held in the Madison Square Gardens,
New York. As receiver a thermophonic arrangement was

* See Electrical Review^ New York, vol. xxxiv., p. 325, 1899 ;
Mechaniker^ vii., p. 236, 1899 ; and E.T.Z,^ xx., p. 459, 1899.

THE SPEAKING ARC.

employed, similar to that already described, but with carbon
threads in place of the ball of cork, which was situated at
the focus of the reflector. The apparatus transmitted
speech at a distance of 1 20 metres.

Fig. 30.
Bell and Hayes' Thermophone with Speaking Arc.

It is not known why Bell did not employ a photophonic
receiver, such as a selenium cell, with battery and telephone
in series, the most probable explanation being that he had
not at the moment a suitable one ready.* In any case

* A historical account which differs essentially from that given
above is to be found in a small volume entitled " The Radiophone,"
which was distributed at the Louisiana Purchase Exposition in St
Louis, 1904, by the American Telephone and Telegraph Co. From
the statements contained in it it appears that Mr Hammond V. Hayes,
an engineer of the above-mentioned company, took up BelPs investi -
gations on the electric arc, probably commencing with those shown
at the Chicago Exhibition. Mr E. R. Cram, an assistant of Hayes',
observed, in April 1897, that the electric arc undulates under the
influence of the weakest of oscillating currents. It is stated that
Hayes then developed from these observations a photophonic trans-
mitter which is identical with the speaking arc. An American patent
relating to this subject is dated ist June 1897. If these statements

WIRELESS TELEPHONY.

it is clear that he had very nearly approached the employ-
ment of a receiver of this kind. Similar researches were

SAUjvuun. CeiL

Fig. 31.
Receiving Circuit of Photophone.

then carried out by Simon* (latterly in conjunction with
Reich) and the author.f

proved trustworthy the priority of discovery of the speaking arc, and
of its application to radiophony, must be awarded to Hayes, since
Simon's first publication dates from the end of 1897 (Erlanger Physico-
Medical Society, 8th November 1897).

Addition by the Corrector, — The American patent concerned. No.
654,630 (completed on 31st July 1900), was filed on 7th June 1897,
and contains the arrangements of the speaking arc shown in Figs.
21, 22, 24, and 25. Both photophonic and thermophonic receivers
were used. Hence the priority of Hayes and Bell in regard to the
speaking arc is no longer a matter of doubt.

* H. Th. Simon, P/tys. Zeitschr.^ ii., p. 253, 1901 ; E.T.Z.^ xxii., p.
510, 1901. That Simon was aware of Bell's adaptation of the speaking
a-rc to the purpose of radiophonic transmission is proved by a letter
to the editor of the Zeitschrift der Mechaniker^ dated 29th September
1899, and published in that journal, vii., p. 237, 1899, in which he
doubts the effectiveness of Bell's arrangement.

t E. Ruhmer, E. T,Z.^ xxii., p. 196, 1901 ; Phys. Zeitschr.y ii., pp. 325

THE SPEAKING ARC.

Passing over a large number of laboratory investigations,
we shall next shortly describe the more important of

Fig. 32.
Ruhmer's Photographophone, Internal Arrangements of Receiver.

Simon's researches,* and then go into the author's numerous
attempts to adapt light-telephony to practical uses.

and 339, 1901. The author had already in 1900 had communications
with the Elektrizitats A.-G. vorm. Schuckert & Co., in regard to this
matter.

* Simon's first demonstration of light-telephony was given at the
meeting of the Physical Society in Frankfort a/M. on the 8th of
September 1900. The condition of his apparatus must, however, have
been very unsatisfactory at that time if one takes into account the
failures which occurred at a later lecture, before the Frankfort
Electrotechnical Society on 6th February 1901, concerning which the
author has written an exhaustive report.

34 WIRELESS TELEPHONY.

Simon's Light-Telephone. — Simon's first experiment
over great distances was carried out at Numberg in
September 1901. A Schuckert's searchlight, with a para-
bolic mirror of 90 cm. diameter and 40 cm. focus, or a
similar apparatus of 150 cm. diameter and 60 cm. focus,

Fig. 33.
Recorder of Ruhmer's Photographophone.

was used as transmitter. At the receiving station a 30 cm.
lens or a 90 cm. mirror was used to concentrate the light on
the selenium cell. Speech was clearly transmitted over a
distance of 1.2 km. with this arrangement* This dis-

♦ Simon and Reich. Demonstration to the Scientific Conference
in Hamburg, 24th September 1901, and Phys. Zeiischr.^ iii., p. 278,
1902, and apparently there was also another lecture on 23rd September
1 90 1. The sender (a Schuckert's searchlight of 80 cm. aperture and
32 cm. focal length) was placed on the roof of the Hamburger
Wilhelm's Gymnasium, the receiver being distant about i km. at the
State Physical Laboratory.

THE SPEAKING ARC. 35

tance was increased to 2.5 km. in a later experiment at
Gottingen. Nothing further has been published on these
researches.

Simon used as transmitter the arrangement shown in
Fig. 23. At the receiving station the apparatus shown
diagrammatically in Fig. 31 was employed. The telephone
and a capacity were connected in parallel with the
selenium cell so that the continuous current through the
cell did not pass through the telephone.

CHAPTER IV.

THE PHOTOGRAPHOPHONE.

The Author's Experiments. — Let us now go some-
what more thoroughly into the author's work on this
subject. These experiments arose from the results already
obtained with the speaking arc in the commencement of
1900. In order to determine the best conditions for photo-
phonic purposes, the author attempted to record the varia-
tions in intensity of the arc when reproducing speech by
means of photography, since they are too rapid to be
observed by the eye directly. For this purpose he employed
a cinematograph of the simplest type. (Figs. 32 and 33.)

Two rollers are placed in a light-tight box and off one
of them on to the other a photographic film is wound with
constant velocity. A small electric motor drives the rolls
so that the film passes with a velocity of several metres
per second. The film travels in front of a cylindrical
lens which concentrates the light of the arc upon it* The
film is afterwards taken off and developed and fixed in the
ordinary way. The finished film shows the variations of
the light just in proportion to their amplitude. They arise
chiefly at the positive crater.f

It was only after many laborious attempts that films so
clear as those shown in Figs. 34 and 35 were obtained.
The alternately light and dark strips which give the appear-

* The original apparatus is now in the German Museum at Munich.

t Birrenbach ("Theory and Applications of the Electric Arc,"
Hanover, 1903, p. 21) shows that about 85 per cent, of the total light
comes from the positive crater, about 10 per cent, from the negative,
and only 5 per cent, from the arc itself.

Fig. 34. Fig. 35.

Photographophonic Records.

WIRELESS TELEPHONY.

ance of great irregularity are in reality exceedingly regular
and harmonic, only changing their order with the change
of the corresponding sound of speech. Each sound gives
its own group of lines and may be easily recognised and
read from the photo-phonographic record.

When the most favourable conditions for the action of
the speaking arc had been determined, to which we shall
return later, we were able to photograph the light varia-
tions with such wonderful clearness that it occurred to us

Fig. 36.
The Reproducer of the Photographophone.

to use the photogram for the reproduction of sound waves,
an idea which was actually realised.

For this purpose the film is made to travel in the
same direction and with the same velocity as when taken,
behind the objective of the apparatus, while the arc lamp,
now silent, is used as a source of illumination. Behind the
film a selenium cell is temporarily fixed, which is put in
series with a battery of small dry cells and a pair of
telephones (Fig. 36). Through the varying strength of

THE PHOTOGRAPHOPHONE. 39

the blackening of the film an illumination of the cell is
produced which corresponds in its variations with the
received sound waves, and is converted into sound in the
telephones.

It is truly a wonderful process : sound becomes elec-
tricity, becomes light, causes chemical actions, becomes
light and electricity again, and finally sound.

When Chladni showed his vibrating plates to the
Emperor Napoleon the latter cried out in surprise, " Mar-
vellous, this Chladni lets us see sounds!" To-day we
have achieved something further. Not only can we see the
tones but can hear again the visible sounds ; we fix the
music and speech which has become light on a gelatine
strip, which retains them until all the sensations are again
called forth which we experienced when the sounds struck
our ears for the first time.

The reproduction of speech by this photographic
phonograph is astonishingly clear, and in strength re-
sembles the ennunciation of a good telephone when in
ordinary use. The instrument has been named the Photo-
graphophone by the author and is shown in Fig. 37. It
has the advantage of the ordinary wax-cylindered phono-
graphs in that the reproduction is purer and is free from
the unpleasant noises caused by imperfections in the me-
chanism.* In addition to this, one can obtain from such
a speech photograph as many reproductions as desired,
each of which will give back the original sounds with equal
exactitude.

While for the production of useful photo-phonographic
records the proper conditioning of the source of light is of
the greatest importance, it is the selenium cell which plays

* Mechaniker^ ix., pp. 75 and 169, 1901 ; Phys, Zeitschr.y ii., pp.
339 and 498, 1901 ; Ann. d, Physik.^ v., p. 803, 1901. The apparatus
was exhibited at the Berlin Polytechnic Society on 12th December
1901, at the Society Railway of Berlin on nth February 1902, and
in the Beethoven Hall of the Philharmonic in Berlin on the occasion
of the Gramophone Concert on 9th April 1903.

WIRELESS TELEPHONY.

the chief part in the reproduction of the sounds. Otie sees
that, among other things, these photographophonic experi-
ments of the author give results which are similar to those
obtained by light-telephony.

o
o

The Selenium Cell. — The necessity of finding a very
sensitive selenium cell was the cause of an exceedingly
thorough investigation of the remarkable properties of

THE PHOTOGRAPHOPHONE.

selenium. A long series of experiments and researches led
eventually to the construction of a selenium cell in a high
degree suitable to the existing conditions.

Further information on this subject is given in the
author's brochure, "Selenium
and its Importance in Electro-
technics," Berlin, 1902, and
also in a paper on the con-
struction and sensibility of
selenium cells, which ap-
peared in the Physicalisclie
Zeitschrifty iii., pp. 468-474
(June 1902).

It may be mentioned that
both flat and cylindrical cells
were described in this paper,
the latter form being pecu-
liarly suitable for use in the
parabolic mirror of a photo-
phone.

Unglazed porcelain or
soapstone is used for the
core of these cells since
selenium adheres firmly to
either. On the surface of
the core fine notches in the
form of a double -threaded
screw are stamped or cut
in which two metal wires
are wound while hot These
wires form the electrodes of
the cell and lead to the
terminals. The pitch of the
double screw is so chosen that the unlike poles of the
cells lie very close to one another. The selenium is put on
in the melted condition so as to cover all the spaces
between the wires, and then is converted into the modifica-

FiG. 38.
Flat Selenium Cell.

WIRELESS TELEPHONY.

tion which is sensitive to h'ght Thus the current flows in
the cell from one wire, the anode, to another wire, the
kathode, through the cell.

In Figs. 38 and 39 are shown flat cells of this form, one
in a polished wooden case with hinged cover, and the other
in ebonite with a sliding lid. The cylindrical cells were
enclosed in an evacuated glass bulb to shield them from
damage and from the effects of the air. The bulb is fitted
with a collar and contacts, so that
the selenium cell may easily be
put into an ordinary lamp holder
(Fig;. 40).

Experiments on the Havel. —

The selenium cells were, however,
not only improved in construction,
but also in quality ; their sensibility
was increased, and, which is quite
as important for practical purposes,
their resistance diminished. Already
in the commencement of 1901 the
author* pointed out that he should
be able to bridge over much, greater
distances with his perfected cells than with those ob-
tainable at that time in commerce. And, in fact, the
author's results with his improved selenium cells, beginning
with small distances in the laboratory and in demonstrations
at the Exhibition of Electrotechnical Novelties in the
Architects' Hall, on 19th March 1902, and in the Imperial
Post Museum on 9th April 1902, were so astonishingly
satisfactory that he was requested to continue the experi-
ments at greater distances.

Fig. 39.
Flat Selenium Cell.

* E.T.Z., xxii., p. 198, 1901.

CHAPTER V.

LIGHT-TELEPHONY AT USEFUL DISTANCES.

The long and laborious researches previously undertaken
in the laboratory now bore fruit, so that on the first attempt
in the laboratory of Nature photo-
phonic communication was estab-
lished at greater distances than had
ever been previously attained to.
The Wannsee near Berlin was chosen
as a suitable field for the experi-
ments. The uninterrupted view over
the broad waters of the Havel and
the possibility of obtaining electrical
energy from the central stations on
its banks rendered the situation pecu-
liarly advantageous.

In addition there was at this time
(summer 1902) a Motor Boat Ex-
hibition, at which the Hagener Ac-
cumulator Company were
showing the electrical
motor boat " Germania,"
which was fitted by Messrs
Schuckert with a torpedo
boat searchlight of 35 cm.
aperture. Through the
kindness of the companies
concerned both motor boat and searchlight were placed
at my disposal for the purpose of the experiments I

Fig. 40.

Cylindrical Selenium Cell Enclosed in

Glass Bulb.

WIRELESS TELEPHONY.

Fig. 41.
Modern Photophonic Receiver.

had in view. When
the arc lamp had been
fitted with a microphone
and transformer, and the
receiver placed in a re-
flector of about 50 cm.
aperture and set up on
a jetty near the Wann-
sce Electricity Works
(see Figs. 41-43), I'ght-
telephony could be
established between the
boat and the land, and
the distance between
the stations gradually
increased by backing
the boat outwards.*

In Fig. 45 a plan is
given which shows the
stretches over which
speech was transmitted.

1. Experiment on the
evening of 4th July.
Right across the Wann-
see, about 1.5 km. Clear
air.

2. Experiment on the
evening of 8th July.
From the Motor Boat
Exhibition, Wannsee
Station, across the
Wannsee towards the
neighbourhood of Neu
Cladow, about 3.8 km.

♦ Also see E. Ruhmer,
E.T.Z.^ xxiii., p. 859, 1902.

DISTANCE LICHT-TELEPHONY.

A-liS«S^»''*Sfe\ JB^V ^^

Fig. 42.
Ruhmer*s Photophonic Receiver on the Wannsee.

Misty. The sending station was in this case on board
the motor boat "Germania," lying at the quay, while
the receiving station was on board the motor boat
" Loreley."

WIRELESS TELEPHONY.

Fig. 43.
Photophonic Reception at Night on the Wannsee.

DISTANCE LIGHT-TELEPHONY.

2 c

u, o

a,
o

3. Experiment on the evening of 9th July. Across the
Wannsee, about 1.6 km. Heavy rain. This experiment
had to be broken off at 1.6 km., because one of the assistants
knocked over the accumulators at the receiving station by
mistake in the dark.

WIRELESS TELEPHONY.

4. Experiment on i6th July, afternoon. In the direction
of Schwanenwerder, about 2.6 km. Weak sunshine.

Since the geographical formation of the Wannsee set

Fig. 45-
Sketch Map of the Wannsee and Havel.

a limit to the extension of the research, a new series of
experiments was undertaken on the Havel, after many
difficulties had been overcome, and were carried on up to
the greatest distance possible under the circumstances.

DISTANCE LIGHT-TELEPHONY. 49

5. Experiment on the evening of 25th July. Receiving
station on the platform of the Kaiser-Wilhelm Tower on
the Karlsberg in the Grunewald ; the sending station on
the " Germania " in the direction of the Pfauen Island near
Potsdam. Thick air, slightly misty.

The transmission was in all cases good, and in this last
experiment surprisingly loud and clear.

As the apparatus was only of the simplest, it was only
possible to telephone in one direction. Communication
with the sending station was therefore established by
means of optical signals, for which purpose a glow lamp
was used in the earlier experiments, and a small stage lime-
light in the later ones (see Fig. 46). In the last experi-
ment, from the Kaiser - Wilhelm Tower, an acetylene
signalling lamp was used.

Berlin Experiments. — As local conditions prevented
the extension of the experiments on the Wannsee or Havel,
and since the limits of the possibilities of the apparatus had
by no means been reached, the author, in the autumn of
1902, in conjunction with Messrs Siemens, Schuckert, atnd
Co., fitted out two permanent stations. Tests were then
made of the system in all different kinds of weather, and
the practical utility of the apparatus correspondingly
increased.

The sending station was at the Berlin works of the
Schuckert Company, in Kopenicker Road, while the receiv-
ing station was at the parish school in the Baumschulweg,
about 2.5 km. distant. A Schuckert*s searchlight with a
very perfect parabolic mirror of 60 cm. diameter was used
as transmitter, while the rece'ver was the same as that used
on the Wannsee except that a somewhat larger mirror of
60 cm. diameter was fitted to it. In order to be able to
speak back, both stations were supplied with apparatus for
transmission and reception. The torpedo boat searchlight,
with 35 cm. aperture (Fig. 48), which had been used in
the experiments on the Wannsee, was installed in the

C/5

DISTANCE LIGHT-TELEPHONY.

Baumschulweg and supplied with current from a battery
of accumulators (Fig. 49). The apparatus shown in Fig.

yiG. 47.

Large Searchlight used as Transmitter.

50 was used in the Schuckert works, its reflector having a
diameter of 45 cm.

The transmission was excellent here also, particularly

WIRELESS TELEPHONY.

as regards the loudness of the enunciation, which, both by
day and in wet weather, was as good as could be desired.
This is all the more remarkable since the positions were
exceedingly unfavourable, the transparency of the air

Fig. 48.
Small Searchlight used as Transmitter.

between the stations being much reduced by the clouds of
smoke rising from numerous factories in the neighbour-
hood, and by the steam and smoke of many railway trains
close by.

DISTANCE LIGHT-TELEPHONY.

Simultaneous Conversations in both Directions. —

Speech was] also transmitted simultaneously in both direc-
tions, the two coincident beams of light from the searchlights
not interfering with one another in any way. Transmis-

•g.

o
o

B
o

sion was possible over this distance with even the small
stage reflector. Fig. 5 1 shows an arrangement of this kind
which is also suitable for demonstrations on a small scale.
Later on, the Baumschulweg station was fitted with a glass

WIRELESS TELEPHONY.

mirror of 90 cm. aperture as receiver in combination with
one of the flat selenium cells previously described (Fig. 52).
The experimental results collected during several months'
work at these stations justified an attempt to considerably
increase the distance. As a suitable point for the receiving
station a water tower on the Falkenberg, behind Grunau in
the Mark, was chosen, which was very kindly put at our
disposal by the superintendent of the garden, Mr Buntzel.
Since there were only three very small windows on the side

Fig. 50.
Portable Photophonic Receiver.

of the tower nearest to Berlin, it was necessary to support
the 90 cm. receiving mirror outside the tower between a
pair of projecting beams, an arrangement which greatly
increased the difficulty of placing the selenium cell exactly
in the focus of the mirror (Fig. 53). The metal reflector
used at first (Fig. 54) was later on replaced by the parabolic
glass mirror from the Baumschulweg, since the latter was a
much better reflector (Fig. 55).

At such distances as these, the spreading of the rays of

DISTANCE LIGHT-TELEPHONY. 55

light from the searchlight is very considerable, the diameter
of the beam being as much as several hundred metres. It
is only when one realises that, without taking account of
the very considerable absorption of light by the air, only
about the one hundred-thousandth part of the light radiated
by the sender reaches the mirror and acts on the selenium
cell, that one obtains a proper estimate of the extreme sensi-
tiveness of the electric selenium-eye.

Fig. 51.
Portable Photophonic Transmitter.

The words spoken into the microphone in Berlin were
still clearly audible at this distance. By using a larger
receiving mirror the distance of transmission might ap-
parently be greatly increased, though of course the stations
would have to be so situated that the curvature of the earth,
already quite appreciable at this distance, did not interfere.

The author's experimental results described above
prove clearly that light-telephony is of practical import-

WIRELESS TELEPHONY.

Fig. 52.
Receiver used in Long Distance Experiments near Berlin.

DISTANCE LIGHT-TELEPHONY.

ance, more particularly in the Navy, for which in the
spring (25th to 28th May) of 1903 the author carried out
some experiments on board the warships " Neptun " and
*'Nymphe," using their ordinary searchlights for the purpose
of light-telephony.

The employment of light-telephony appears possible
even for military purposes. Figs. 56 and 57 show a

Fig. 53.
The Tower and Receiver at Falkcnberg.

portable set of apparatus designed for use in the field.
The searchlight is placed on a waggon and is supplied
with current from a portable petrol motor and dynamo.
The receiving apparatus is made as simple and as light as
possible so that it may be easily moved from place to place.
The author continued his researches in 1904 in order
to improve his methods still further. The transmitting

WIRELESS TELEPHONY.

station was placed on the electric barge " Teltow " (Fig. 58),
with which some experiments were made on the Grieb-
nitzsee (near Neu-Babelsberg) and on the Havel.

Another station was erected later on the tower of the

H
I

Astrophysical Observatory on the Brauhausberg, near
Potsdam, by permission of Dr H. C. Vogel (Fig. 59).
The transmitter was a searchlight of 60 cm. enclosed in
an aluminium case and standing on a tripod. The receiver

DISTANCE LIGHT-TELEPHONY.

was first placed on the "Teltovv" and later on a tower of the
Royal Castle on the Pfingstberge, near Potsdam.

It was hoped to continue, the experiments as far as the
water tower in Steglitz (20 km.), or even to Marienberg,
near Brandenburg a/H., which would have been a distance
of 37 km., but they had to be broken off because the
searchlight was required for use in the operations in South-

1 Jlr><

'IE A

1 ^^■^

HI '1'

v^,^_^^^^|

Fig. 55.— Adjusting the Receiver.

West Africa, and a similar one was not to be had, while a
heavier one could not be put on the tower, and a smaller
was not sufficiently powerful.*

We shall now consider the most favourable conditions
as they have been determined by these very numerous
experiments.

♦ The apparatus used in the Wannsee experiments was shown
at the recent Exhibition of Inventions at the Zoological Gardens in
Berlin. (See Figs. 59A, 59B.)

WIRELESS TELEPHONY.

Best Conditions for Light-Telephony. — In the trans-
mitter the chief part is played by proper superposition of
as large as possible microphone currents on the supply
current of the arc lamp. For this purpose an exceedingly

sensitive microphone, which will stand a large voltage and
carry a considerable current, and a properly designed trans-
former are necessary. In the speaking arc, where large
changes of volume are required, a long arc is best. Here,

DISTANCE LIGHT-TELEPHONY.

on the contrary, we need large variations of the intensity
of h'ght radiated, since it is on these variations and not on
the total amount of light radiated that the transmission
depends. It is therefore advantageous to keep the arc
small and to use as little
current as possible. The
less the constant supply
current of the arc, the
greater, in proportion, are
the variations due to the
microphone current, and
therefore the greater are
the variations of the radia-
tion from the positive
crater of the arc. As we
have seen above, these
variations of the in-
tensity of the light are
only observable if the
current in the arc be
small, and they become
less and less as it in-
creases, until with very
large currents, such as loo
amperes or more, the
brilliancy is no longer
proportional to the cur-
rent, and hence the oscil-
lations of the latter do
not affect the former, so
that there is no conver-
sion of electric into light
waves.

It appears thus, that
increase of it causes an

FiG. 57.
Military Receiver.

if the current be small any
increase of the temperature
of the positive crater, while if it be large the tempera-
ture remains constant and the crater only increases in

WIRELESS TELEPHONY.

C/3

size.* The use of a positive crater of small diameter is
also of importance on account of its position in the focus

* F. Nerz, " Scheinweifer und Fernbeleuchtung," Stuttgart, 1899 ;
O. Krell, " Der Gegenwartige Stand der Scheinwerfertechnik/'
Vortrage, Schiflfbautechnische Gesellschaft, i8th November 1904.
See also M. Reich, F/tys Zeitschr, vii., p. 73, 1906 ; particularly
section 15, p. 85.

DISTANCE LIGHT-TELEPHONY.

of the mirror, its exact adjustment being less necessary
than in the case of a larger crater.

The less the area of the source of light the less is the

H
I

divergence of the beam of light reflected from a properly
ground mirror, and therefore the greater is the amount
of light collected by the mirror of the receiver and con-
centrated on the selenium cell.

64 WIRELESS TELEPHONY.

t
As the theory of the paraboh'c mirror shows, it is

possible to reduce the divergence of the beam from a large

source of light by increasing the focal length of the mirror.

This must always, however, go hand in hand with an

increase of the diameter of the mirror in order that as

great a proportion of the light may be used.

It is therefore necessary in researches on light-telephony
to use a properly figured parabolic mirror with good reflect-
ing surface and large aperture and focal length, in the focus
of which is placed an arc lamp fed by the smallest practic-
able current.

The large Schuckert's searchlight, with its almost
mathematically perfect parabolic glass mirror, silvered on
the back, served the purpose excellently; and yet with
this, even though a very small arc was used, the divergence
at great distances was very considerable, as we have seen
in the Grunau experiments. From 2 to 3 amperes were
used as a rule, though for great distances from 4 to at most
10 may be used with advantage. With greater currents the
loudness of the transmitted speech becomes notably less.*

For small currents carbon rods of 5 mm. for the positive
and 4 mm. for the negative electrode are sufficient ; while
for larger currents carbons of from 8 to 6 mm. are suitable.
The material of which the electrodes are formed is of con-
siderable importance, since the temperature of the crater
must vary rapidly, and large thermal capacity of the
electrodes hinders this variation. If a solid carbon be
used, the constant shifting of the positive end of the arc,
which occurs even more with a metal anode, is so trouble-
some that for practical uses a soft cored carbon, which fixes
tjie point at which the arc terminates, is preferable. The
longer and the more unstable the arc (from 4 to 7 mm.

* This is one of the causes why the light-telephonic apparatus at
the St Louis (1904) Exhibition worked badly. The supply current of
the sender was about 20 amperes. The receiving station is shown
in Fig. 60.

DISTANCE LIGHT-TELEPHONY.

with 60 to 90 volts) the better are the results obtainable.
The loudness of the transmission is quite astonishing at

the moment the arc breaks, as the latter is then attached
only to a single point on the electrode. The effects of
higher voltages were investigated during the experiments

WIRELESS TELEPHONY.

on the boat "Teltow/* but little advantage was found in
using more than the usual arc voltage of 60 to 90 volts
with a supply current at 1 10 volts.

There are no further factors which require consideration

in the transmitter ; only the discovery of a new source of
light with a greater specific brilliancy could lead to a further
advance.

We come next to another important point, namely, the

DISTANCE LIGHT-TELEPHONV.

proper direction of the searchlight beam towards the
receiver. This adjustment is often very difficult, particu-
larly from a moving platform such as a ship's deck. In
this case it is necessary to suspend the searchlight on
gimbals. In the evening and at night the person in charge
of the sender sees the beam of light, and, if the distance
be not too great, the
reflection from the illu-
minated receiving
mirror. At greater dis-
tances, however, say from
3 km. upwards, one can-
not recognise illumi-
nated objects, and by
day, of course, the beam
is invisible and it is im-
possible to observe its
direction. The search-
light must therefore
have a telescopic sight
attached to it whose
axis is parallel with the
axis of the searchlight.

Atmospheric Con-
ditions. — In order to
correct a widely diffused
error we may here state
that the results by day
are quite as good as

those by night Indeed, one may even illuminate the
selenium cell by means of a powerful but constant source
of light without in any way reducing the loudness of the
transmission. Direct sunshine must, however, not be
allowed to fall on the mirror at the receiving station or the
selenium will be melted and the cell rendered useless. In
cases in which it is necessary to direct the mirror towards

Fig. 6o.
Receiver at the St Louis Exhibition.

68 WIRELESS TELEPHONY.

the sun, it is only needful to shelter it from the direct
sunshine by means of a screen projecting above it.

The transparency of the atmosphere is of the greatest
importance, both as regards range and clearness of trans-
mission. When one considers that the atmospheric absorp-
tion varies from 2 to 50 per cent, per km., and even more
than this, one can understand the great influence of this
factor. Rain and snow affect transmission, but not to the
extent one would expect. In thick fog light-telephony is of
course impossible over anything but the smallest distances.*

Recemng Apparatus. — Let us consider finally the
more important factors at the receiving station. The larger
the reflector the more light is concentrated on the cell, and
therefore the greater are the variations of illumination and
of the currents in the microphone circuit. It is not im-
portant that the mirror should be exactly parabolic, as the
light is concentrated not on a point but on the relatively
large sensitive surface of the cell. The mirror must, how-
ever, be made of a material which has a high coefficient of
reflection. I n place of the exceedingly expensive Schuckert's
glass searchlight reflectors one may use for this purpose
metallic mirrors, the best being of German silver, which
may be constructed comparatively lightly and cheaply in
large dimensions.

Cylindrical selenium cells should be used with mirrors
of short focal length, and flat ones if the focal length be
longer. With very large receiving mirrors the latter form
is preferable, ?>., a somewhat flat mirror should be chosen
whose focus is outside the body of the mirror, and a flat

♦ In southern countries the transparency of the atmosphere is
much greater than in Europe. I have been informed that heliographic
communication has been maintained up to distances of 100 and even
160 km. between Haribiband Outjo and Windhukand Keetmanshoep
in South- West Africa. See also LoebelPs " Jahresbericht iiber das
Heer u. Kriegswese ," 1906.

DISTANCE LIGHT-TELEPHONY. 69

cell should be employed. At very large stations a number
of mirrors might be used instead of a single one. The
author has designed an arrangement of this kind in which
six mirrors of 2 metres diameter surround a seventh, and
hoped to obtain a range of 100 km. with it. The plan has,
however, not yet been carried out

The selenium cell has naturally a very great influence
on the receiver. We have already made clear the points
of view which determine the choice between a cylindrical
and a flat cell. In order to obtain the greatest increase of
the intensity of illumination, which obviously depends on
the relation of the area of the mirror to that of the cell, the
latter must be as small as possible. Electrical conditions,
however, set a limit to improvement in this direction. Small
cells have so great a resistance to the electric current that
a battery of many hundred volts would be required to
produce a current sufficient to actuate the telephone. The
use of such high voltages is, however, impracticable. One
uses, therefore, cells which strike a mean between the two
opposed conditions, and have a relatively small surface
while retaining a relatively low resistance.

The cell must be illuminated over its entire surface by
light which is as nearly perpendicular to it as possible. It
is a great mistake to illuminate only a part of the sensitive
surface with the undulating light, as in this case the unillu-
minated part forms a mere dead weight on the illuminated
and active part, so that the current variations are seriously
diminished.
"^ While the author commenced his researches with

cylindrical cells of 50 mm. length and ft mm. diameter, he
later employed those of 25 mm., and finally of 12.5 mm.^
length. For many experiments cells of similar length but
of only 9 mm. diameter proved very suitable after a method
had been found of constructing these with a sufficiently low
resistance. In practical experiments cells of the third type
were almost exclusively used. The resistance of these cells
in the dark should not be more than 25,000 ohms. Flat

70 WIRELESS TELEPHONY.

cells wprk best when the diameter of the selenium plate is
about 25 to 30 mm.

While in the method of construction used by the author
the cylindrical cells are shielded from the influence of the
atmosphere by their position inside an evacuated glass
tube, the flat cells must be protected in some other way ;
if used in the open air, a metal capsule with a glass window
in it may, for instance, be used. With the high voltages
used in connection with the cells the least deposit of
moisture from the air causes short circuits and electrolytic
actions, which soon destroy the cell.

Having discussed in the foregoing paragraphs the best
size and shape of cell, we must now take into consideration
their essential properties. The value of a cell depends not
only on its sensibility to variations in illumination, but in
great measure on the rapidity with which its resistance
alters. Thus cells for use in light-telephony must have
very little inertia. These conditions may be attained to a
certain extent by proper construction and preparation of
the cells. For instance, the sensitive layer must be as thin
as possible in order that all the active material may be
exposed to the action of light. If thick layers of selenium
were used the resistance of only the uppermost skin would
be reduced by the illumination, since crystalline selenium
is almost perfectly opaque. The sensibility of the cell is
different at different points on its characteristic curve, /.e\,
on the curve showing the relation of resistance to illumina-
tion. The amount of the variation due to any slight change
of illumination is thus dependent on the total intensity of
the illumination as well as on the amount of its alteration.
As a rule, the illumination is too weak in practical working
to do any harm, and at the same time it must be remem-
bered that illumination reduces the resistance, and is there-
fore in this sense beneficial. The two actions thus com-
pensate one another to some extent. Under certain
circumstances the desired result may be obtained by using
a cell with a known and suitable characteristic. There are

DISTANCE LIGHT-TELEPHONY. /I

then so-called " weak " cells, which are more sensitive when
faintly illuminated than in a bright light, and also cells,
usually called "hard," which give better results when
strongly illuminated. In general, however, the former
type is most useful since it is as a rule more sensitive
than the latter.

At first sight one would think that by raising the
voltage applied to the cell the variations of current would
also be increased, at least so long as the current was not
so great as to damage the cell. It has been found, however,
that though carefully constructed cells in which the distance
between the electrodes is made as uniform as possible may
be driven pretty hard before they are burnt through, there is
in every case a best illumination and a best working current,
and that only under these conditions does one get the
maximum oscillations. If the current is increased beyond
this by raising the voltage, the useful action decreases.
The theory of this experimental result has not yet been
made clear. It is probably to be attributed to the Joulean
heat, since heating of the sensitive layer appreciably re-
duces the sensibility of the cell. For this reason it is
advisable, in experiments at short distances, to filter off
the heat rays which radiate from the transmitter. At
greater distances (i,ooo metres and more) this precaution
is unnecessary, as the atmospheric absorption is so great
that no special apparatus is required.

CHAPTER VI.

BEST WORKING CONDITIONS FOR LIGHT-
TELEPHONY.

Finally we must go into some points which are of
essential importance in the attainment of satisfactory
working.

Best Colour of Light. — We know that the light which
radiates from the positive crater consists of undulations.
Which wave-length, then, of this white light is it that is
mainly the cause of the action? The author has made
many researches in this direction and has found that, most
unexpectedly, the ultra-red and red, and the violet and
ultra-violet rays are of most importance. It is therefore
advantageous to employ selenium cells which react most
definitely with the corresponding wave-lengths. This may
be effected, as the author has shown, by the use of sensi-
tisers, without which the maximum sensibility of selenium
is to the yellow part of the spectrum. A similar artifice has
long since been applied to the preparation of photographic
plates*

Practical experience has shown that at great distances
there is no advantage in using cells which are specially
sensitive to waves of short length, as the atmospheric
absorption is so great those which reach the receiver are of

* See also J. S. Dow, Electric Review^ London, lix., p. 729, 1906.
The absorption of the light as it passes to and fro through the glass of
the searchlight reflector, and also through the glass tube of the
selenium cell, plays a certain part in the phenomena.

WORKING CONDITIONS. 73

very small intensity ; it is all the more important, therefore,
to increase the sensibility for longer waves, on the one
hand because it is the red rays which vary most in the
transmitter, and on the other because it is these which
are least absorbed of all the visible rays by the atmo-
sphere. To this latter circumstance we must attribute the
fact that at great distances the light of a searchlight appears
to be distinctly red.

It might be thought that the conditions would be im-
proved by using carbons chemically prepared to give a red
light in the searchlight. This is not, however, the case, as
the materials added only colour the arc itself and make no
essential difference in the spectrum of the positive crater,
which is the only source of light employed in a searchlight.
Indeed it is no consequence, when using cells which have
been sensitised for red light, whether the light from the
searchlight is used directly or through a colour filter.

Monochromatic Cells. — Selenium cells which are sensi-
tive to different colours also make it possible to transmit
several conversations over one beam of light. If several
searchlights are placed near one another at the sending
station, each being provided with a light filter of different
colour, their beams will blend in the atmosphere, and if the
colours have been properly chosen will produce a ray of
white light. At the receiving station the light will therefore
appear to be radiating from a single uncoloured searchlight.

If, now, each searchlight is separately acted on (in the
case of their having a common source of current supply it
is necessary to take means to prevent the oscillations from
spreading from one lamp to another), conversations trans-
mitted simultaneously from the sending station may again
be separated at the receiving station if a number of corre-
sponding receivers be used, each of which is sensitive only
to one of the colours transmitted. If an ordinary selenium
cell were used a confusion of all the voices would be heard
at once.

74 WIRELESS TELEPHONY.

Another application of the colour-sensitive cells consists
in the author's method of preventing conversations being
overheard by others than those directly concerned. It
may first be remarked that of course it is impossible to do
this in any case unless the receiving apparatus is placed in
the actual beam of light from the searchlight

Secret Communications. — The method for ensuring
secrecy depends on the following principle. Since the
transmission of speech is only through variations of light,
it is of no consequence whether positive alterations (in-
creases) or negative alterations (decreases) are employed,
and similarly the effect is the same in photo-phonographic
reproductions, whether one uses the original negative film
or a positive print taken from it. Now the arc lamp will
give the one or the other effect according to the relative
direction of the microphone current and the supply current.

If one now employs as transmitter two searchlights
controlled by the same microphone, which is arranged to
produce positive variations in one arc and negative in the
other, and allows their beams to mingle, it is clear that,
since the variations are equal and opposite, the total effect
on the receiver will be nil. By placing complementarily
coloured light filters in front of searchlights the two beams
will still, when mixed, produce an ordinary white which
will be without effect on an ordinary cell, but if a cell which
is sensitive only to the light given out by one or the other
of the searchlights be used it will respond at once. By
using two receivers their actions may be superposed in the
same direction on a telephone common to both circuits.
Only the person called, who knows the exact wave-length
used, can hear the voice in undiminished loudness, while no
one else, in spite of the fact that his selenium cell may be
illuminated, can receive anything.

Uses of Light-Telephony. — In x:onclusion, we must
say a few words on the practical importance of light-

WORKING CONDITIONS. 75

telephony. In the first place, there is its use in the navy,
where communications may be kept up by its means
between ships, whether lying in harbour or in motion.
And since their ordinary searchlights may easily be adapted
to this purpose, the cost of installing the apparatus is small.

Light-telephony is also very suitable for communication
between lighthouses and ships.

Even in the army, for communication between outposts
and headquarters, or between besieged fortresses and the
relieving armies, its use appears possible.*

Finally, light-telephony appears to be a most useful
substitute for the heliograph, with which the rate of trans-
mission does not exceed 200 words per hour.

Light-telephony possesses all the advantages and dis-
advantages common to every directed method for the
transmission of news.

It has one important advantage, namely, that no one
can read a message unless the beam of the searchlight is
actually directed towards him, and then only with a proper
apparatus. We have shown that there are other ways in
which secrecy may be maintained.

It is, of course, impossible to read directly from the
vibration of the beam of light, as its motions, corresponding
as they do to waves of sound, are far too rapid for the eye
to follow even if they were otherwise readable, which they
are not, as they only resemble a phonographic tracing.

As a disadvantage must be noted the fact that the
distance of transmission is limited by the curvature of the
earth, though in actual working this is not of great con-
sequence since this form of telephony is particularly suitable
for small distances, where a simple and rapid method of
communication is required. At greater distances telegraphy
takes the place of telephony, as in transmission over the
wires.

♦ As for instance when General Buller got into communication
with Ladysmith during the Boer War.by means of the heliograph.

^6 WIRELESS TELEPHONY.

We must further consider those questions of light and
shade which concern the transmission of speech by means
of light. On the one hand, the use of visible rays makes
the determination of the proper positions of the sender and
receiver easy; but on the other hand, this very visibility
of the beam of light is a disadvantage at night, especi-
ally for military purposes, since an enemy can at once
observe the positions of the transmitting and receiving
stations.

A further disadvantage, which is particularly obvious in
transmission over great distances, is the absorption of the
short-waved visible light by the atmosphere, especially
during fog.

Ultra-Red Rajrs. — These latter difficulties may, how-
ever, be considerably reduced by the use of the invisible
ultra-red rays which are of greater wave-length. Experi-
ments with these have already given great promise. A
selenium cell, bolometer, or thermopile may be used as
receiver, while in the beam of light from the sender a thin
plate of ebonite is interposed which allows the longer waves
to pass in almost undiminished intensity, though completely
absorbing the visible rays — a fact observed some time ago
by the author.*

By the use of such a filter transmission may be main-
tained although the beam connecting the sender and
receiver is rendered quite invisible. A demonstration of
this method was given by the author at the Exhibition of
Electrical Novelties of the Electrical Society of Berlin on
19th March 1902.! The system has not yet been tried at
great distances.

Putting together all that has so far been said, we find
that we possess in electric light-telephony a convenient,

* See also lecture by Perry, " On the Future Development of
Electrotechnics," Society of Arts, London, 24th March i88a

t See E,T,Z.^ xxiii., p. 643, 1902, and MecJtaniker^ x., p. 66, 1902.

WORKING CONDITIONS. 7^

secret, and certain method of communicating up to dis-
tances of about 6 to 8 km., at which distances only the
thickest smoke or fog can render it uncertain.

Ultra- Violet Rays. — In connection with telephony by
means of light and heat rays we may mention Sella's
system, in which ultra-violet rays are employed for the
transmission of speech. This form of wireless telephony
is very like Zigjcler's electric light telegraph,* and depends
on Heinrich Hertz's observation that the sparking distance
between two electrodes is increased when
ultra-violet light falls on the negative con-
ductor.! If, for instance, the spherical
electrodes of an induction coil be separated
so far that the induced potential is no longer
able to cause a spark, sparking will recom-
mence if a beam of light rich in ultra-violet
rays be allowed to fall on the negative
electrode. This phenomenon is still more
marked if the discharge takes place in
rarefied gases. The containing walls of Fig. 6i.

the vessel in which spark takes place must, Discharger
of course, be transparent to ultra-violet
rays. Ordinary glass is not suitable for this purpose.
Zickler used a platinum plate and metal ball in a glass
vessel, one side of which consisted of a platd of quartz (see
Fig. 6i). The plane electrode is turned at an angle of 45
deg. to the axis of the vessel, so that the active electrode
may be illuminated by the rays entering through the quartz.
The best air pressure was found to be about 200 mm. of
mercury. In front of the tube is placed an adjustable quartz
lens in order that the rays from the transmitter may be con-
centrated on the cathode. Sella employed a receiver of this

* K. Zickler, E.T.Zs, xix., pp. 474, 487, and 826, 1898.
+ H. Hertz, Wied, Ann,^ xxxi., p. 983, 1887 ; Wiedemann and
Ebert, IVied. Ann., xxxiii., p. 241, 1887 ; xxxv., p. 209, 1888.

78 WIRELESS TELEPHONY.

sort in conjunction with a telephone for wireless tele-
phony. To supply the tube with high tension direct
current, an electrical machine maybe used. As transmitter,
one of the photophonic arrangements described above
may be employed. The periodic variations in the illumi-
nation of the cathode are thus reproduced in the tele-
phone as sound waves. Dussaud has shown that instead
of the tube a fluorescent body placed near a selenium cell
may be used. Under the influence of the ultra-violet
rays the fluorescent plate gives off" rays of light which act
on the selenium cell, and hence the sound waves may be
reproduced in a telephone connected to the latter.

It is hardly to be expected that these systems due to
Sella and Dussaud will attain to practical use, since the
absorption of ultra-violet light is so great even in clear
weather.

Let us now turn to wireless telephony by means of
electric forces, and in the first place to hydro-telephony, in
which the transmission is effected by currents in the earth
or sea.

PART II.

WIRELESS TELEPHONY BY MEANS
OF ELECTRICAL FORCES.

CHAPTER VII.

CLOSED CIRCUIT TELEPHONY,

Closed Circuit System. — The spreading out of the current
between two electrodes placed on an unlimited conductor
is the physical foundation of these methods. In Fig. 62
are shown the stream lines of the current between two
electrodes, A and B, placed in water or damp earth. As one
sees, the lines do not go straight from one electrode to the
other, but spread themselves out in curves through the
entire conducting medium. Those in the neighbourhood
of the straight line between the stations lie close together,
while further out the density of the lines is less. If two earth
plates be connected by an insulated wire at points reached
by the current a proportion of the latter will pass from one
to the other by the wire, and the greater the conductivity
of the wire the greater will be the current which it carries.
In this way a certain fraction of the energy sent out by the
transmitting station is picked up, and actuates the receiver.
The two stations thus form what is in some respects a single
circuit*

♦ See J. Erskine- Murray, "Handbook of Wireless Telegraphy,"
p. 2, London, 1907.

WIRELESS TELEPHONY.

The two earth plates should be placed on the same
stream line, the most favourable position being when the
receiving and sending conductors are parallel.

If the earth plates are placed so that the receiving wire is
perpendicular to the stream lines of the current, and therefore

Fig. 62.
Lines of Flow between Two Electrodes.

has its ends on the same equipotential surface, transmission
will not be possible, as no current will flow through the wire.
A transmitter for wireless telephony on this principle,
therefore, consists essentially in an arrangement for produc-
ing oscillatory currents corresponding to the waves of sound,
and for conducting these currents to two plates in the earth
or sea.

CLOSED CIRCUIT TELEPHONY.

The receiver consists of two plates similarly oriented to
the first pair, which are connected by an insulated wire
through a telephone (Fig. 63).

Fig. 63.
Receiving Circuit for Closed Circuit System.

In order to make the total resistance as low as possible
it is best to use a low resistance telephone.

Experiments made, so far, on this method, differ only
in regard to the transmitting apparatus. '

Fig. 64.
Transmitting Circuit for Closed Circuit System.

The simplest of these is shown in Fig. 64. In place of
the direct connection of the microphone to the earth plates
a transformer may be used (Fig. 65).

WIRELESS TELEPHONY.

Attempts were made by Ducretet in 1902 to telephone
over land by this method. He shows experimentally
what had already been deduced theoretically, namely, that
the greater the distance between the stations, the greater
must be the distance between the earth plates, and that the
latter also depends on the nature of the soil.* Using a
base line of 60 metres, Ducretet transmitted speech over a
distance of 1,000 metres.

M B

V\AM

Fig. 65.
Transmitter for Closed Circuit System.

The experiments carried out by L. Maiche since 1900
at Castle Marcais on the Marengo estate of the Prince of
Monaco are on the same principle. A base of 20 metres is
found to be sufficient for a range of 400 metres. The
limit of transmission of telephonic speech was at first given

* Coinptes RenduSy B. 134, p. 92, 1902 ; Electrician^ xxiii., p. 67,
1902 ; and Rev. Ind.y xxxiii., p. 34, 1902. See also Gavey and Preece's
experiments, p. 89 below.

CLOSED CIRCUIT TELEPHONY. 83

as 4 km., but later news is to the effect that a distance of
7 km. has been reached with a base of 450 metres.*

Finally we may mention the experiments of Armstrong
and Orlingt (1902), of the author (1902), and of Engisch J
(1904).

The Author's Experiments. — The author attempted
to use this system during his experiments in light-tele-
phony on the Wannsee, to provide a means of communi-
cating back from the boat to the shore, but the short base
available on board the boat, and the necessity for keep-
ing it end-on to the shore station when moving the
boat from place to place, rendered the working unsatis-
factory.

In order to attain to a considerable range, either the
distance between the earth plates must be very large, or
the energy sent out by the microphone current must be
much increased.

In place of an ordinary granular carbon microphone a
so-called heavy current microphone may be employed which
carries a more powerful current, or an arc may be used as
transmitter, either by speaking directly to it (see Fig. 28),
or by connecting it to a microphone § (Fig. 66),

Actual experiments with these improved transmitters
have, however, given no better results than those with the
simpler apparatus described above.

♦ Electrical Review^ London, 1., No. 1263, 1902 ; also German
patent, No. 134,996, of 22nd August 1901. See " Fur alle Welt," p.
373, 1902.

t Electrical World and Engineer^ xlvi., p. 11 22, 1905.

X Further information in Zacharias u. Heinicke, * Prakt. Handbuch
der drahtlosen Telegraphie und Telephonic," Vienna and Leipzig,
'907» PP- 219-221.

§ Richard von Horwarth, Sigmund Musits, and Dr Stefan Hagyi
Ristic, Austrian patent. See also American patent. No. 777j2i6 of
24th November 1902. A. F. Collins, Western Electrician^ xxxviii.,
p. 292, 1906; and -£". TIZ., xxvii, p. 1073, 1906. H. M osier, ^. T'.Z.,
xxvi., p. 490, 1905.

WIRELESS TELEPHONY.

Open Circuit Sjrstems. — Finally we must mention
Mosler's system in which earth conduction is also used, but
differs from the others in that large variations of the voltage
and small currents are employed in place of large currents
and small voltages.

JWWWV — I

Fig. 66.
Arc Transmitter for Closed Circuit System.

The transmitting apparatus is shown in Fig. 67.

The oscillatory microphone currents are brought to a
high voltage by means of a transformer, only one pole of
which is earthed, the other remaining disconnected. At

CLOSED CIRCUIT TELEPHONY.

-(2>

the receiving station, a telephone earthed on one side only
is' employed. The telephone has a metallic cover which
is touched by the observer when listening.*

The use of an aerial wire at the receiving station proved
of no advantage. Some increase in the loudness of trans-
mitted speech took place, however, when the free end of
the wire was held in the hand.

The transmission could be further improved by attach-
ing a bobbin of copper wire to the free end of the secondary.
If both poles of the induction coil were earthed the trans-
mission was very much
weakened, though under
certain circumstances it
was possible to obtain
good transmission when
both ends of the tele-
phone at the receiving
station were earthed.
If A in Fig. 68 represents
the earth plate at the
transmitting station,
and B, C, D the earth
plates at the receiving
station, T the telephone,
and E a switch by means
of which either of the
earth plates c or i) may
be connected to the tele-
phone, it is found that
there is practically no transmission if the plates B and C
are connected to the telephone.

Mosler concluded from this that the high tension micro-
phone current which flows into the earth by the plate A

nil

Fig. 67.
Open Circuit Direct Transmitter.

* Mosler's apparatus is somewhat similar to Dolbear's, American
patent, dated 1882. (See Erskine- Murray, " Handbook of Wireless
Telegraphy," p. 34, London, 1907, also p. 92 below.)

WIRELESS TELEPHONY.

causes rhythmical electrifications of the earth which spread
out with decreasing intensity.

T(^

Ob DC

Fig. 68.
Proof of Radial Flow with Open Circuit Transmitter.

Fig. 69.
Closed Circuit Receiver with Open Transmitter.

Limits of Closed Circuit Systems. — Transmission of
speech can only be obtained when points at different

CLOSED CIRCUIT TELEPHONY. 87

potentials, i,e,^ at different distances from the sending
station, are connected through the telephone, since in this
case only does a current flow through it (Fig. 69). Trans-
mission of speech without a second earth plate was obtained
by earthing the telephone by holding the metal cover in
the hand. The earth plate was fortunately so placed that
it was possible to obtain an extensive variation of the
distance in radial directions. Later experiments showed
that it was not impossible to achieve transmission over
several kilometres, especially over water, if larger trans-
formers and microphones which could stand heavier
currents were employed. Mosler himself, however, declares
his system does not provide a solution of the problem of
wireless telephony at great distances. Hydro-telephony
can thus hardly be said to have attained to practical
importance.

CHAPTER VIII.

ELECTRO- MAGNETIC INDUCTION
TELEPHONY,

In this the transmission is by means of electro-magnetic or
electro-static induction. In the first of these methods the
varying magnetic induction is caused by the variations of
the microphone current, while in the second case variations
in the electric charges are the cause of the action.

According to recent Maxwellian theory there is no
difference between an electrical force of electro-magnetic
origin and an electrical force of electro-static origin.

The simplest case of induction telephony is cross talk
in a telephone system, />., when words spoken on one wire
are heard on a telephone attached to a parallel but separate
line.

Trowbridge, of Harvard University, was the first to
examine this phenomenon systematically.

In his experiments he employed two coils consisting of
many turns of insulated wire (Fig. 70).

In the transmitting circuit were a microphone and
battery, and in the receiving circuit a telephone. In the
latter circuit the induced currents cause motions of the
telephone diaphragm in unison with the sound waves
which actuate the microphone of the transmitter. Trans-
mission can only be obtained at relatively short distances
by this method. Since the oscillatory currents in the micro-
phone circuit are limited by the carrying capacity of the
microphone, the transformers required in order to obtain
transmission over considerable distances would have to be

INDUCTION TELEPHONY.

of impracticable dimensions. The method is on this
account of no practical importance.*

We may here briefly describe the experiments of M. R.
Hutchison at the St Louis Exhibition.

The transmitting circuit consisted of a large wire cable
in series with a battery and microphone. The portable
receiver was a coil of 30 cm. diameter wire in several
layers, with two telephones in series (Fig. 71).

The distance to which speech was transmissible with
this apparatus was naturally small.f

B i-

Fig. 70.
Electro- Magnetic Induction Telephony.

Gavey and Preece. — The experiments and work of
Gavey and Preece, which commenced as far back as 1894,
have given more satisfactory results J

Gavey 's first experiments were across Loch Ness, in the
Scottish Highlands.§

* E. Wilson and C. J. Evans used the larger current of an arc
influenced acoustically or magnetically, instead of the weaker micro-
phone current. The Electrician^ xlviii., p. 46, 1901.

t See also L. Maiche, French patent, No. 376,100.

X E,t.Z.^ xxi., p. 812, 1900.

§ British Association Report, 1894.

WIRELESS TELEPHONY.

With an average distance of 2.1 km. between them, two
wires were suspended parallel to one another on opposite
sides of the loch, and their ends well earthed. The length
of each was about 6.5 km., and their average distance apart
2.1 km. In series with the sending conductor was placed a
Deckert's microphone and a battery giving 14 volts. A tele-

Fic. 71.
Hutchison's Experiments.

phone was placed in the receiving circuit. Words spoken
into the microphone were audibly repeated by the telephone.
That better results were obtained in this experiment
than in those previously described may safely be attributed
to the fact that in addition to the induction between the
circuits the earth currents were by no means negligible.
This method, therefore, depends on a combination of hydro
and induction telephony.

INDUCTION TELEPHONY. 9I

Preece in 1899 carried out further experiments of a like
nature across the Menai Straits, an arm of the sea lying
between the counties of Anglesey and Carnarvon, and found
that the reception was best when the earth plates at the
ends of the parallel wires were sunk in the sea, ue.y that
under these circumstances it was possible to make a con-
siderable reduction in the length of the wires without
hindering the transmission.

Skerries. — A practical use for this nieans of communi-
cation was soon found in the establishment of a telephonic
connection with the lighthouse on the Skerries, a rocky
island off the coast of Anglesey, where the roughness of
the sea bottom and the strength of the tidal currents
rendered the use of a cable impossible. The distance from
the land station at Cemlin was about 4.5 km.

The installation consists of a wire about 700 metres
long on the island, and a parallel wire of about 5.7 km. on
Anglesey. The ends of both wires were attached to plates
sunk in the sea. Transmission proved so good that the
installation is still in operation.

Rathlin. — Shortly afterwards Gavey connected the
island of Rathlin with the north coast of Ireland by means
of a similar installation, the distance in this case being
1 3 km. The conductor on the island was 2 km. long, and
that on the mainland 9 km.

Attempts have also been made to establish communica-
tion between ships, and from ship to shore, by this means,
in which case the conductor was carried along the length
of the ship at the height of the topmasts, and was connected
to plates in the sea.

A more extensive use of this system is, however, as
little to be expected as is that of hydro- telephony, — the
chief objection being the necessity for very long parallel
wires, whose length, indeed, must be such as would nearly
serve to bridge the actual distance between them.

WIRELESS TELEPHONY.

It is very probable that the experiments of Valle and
Ph'sner at Trieste, about which some notices appeared a
few months ago, are of a similar nature, though as yet no
details have been given.

M(0)

I E

Fig. 72.
Dolbear's Open Circuit System.

In conclusion, we shall describe some arrangements
which depend on electro-static induction.

INDUCTION TELEPHONY.

Dolbear. — A. E. Dolbtear utilised the charge on a
capacity area, such as a gilded kite at the top of an aerial
wire, which was varied by means of a microphone — the
variations corresponding to the sound waves spoken into

I E

Fig. 73.
Edison's Railway Wireless Telephone.

the latter. For this purpose the capacity C was suspended
at a suitable height above the ground, and was connected
to a transformer and to a battery of 100 volts or more, the
other terminal to the battery being earthed (Fig. 72).

94 WIRELESS TELEPHONY.

At the receiving station a similar capacity area was
elevated and connected, through a telephone, to earth.

The oscillations of potential in the transmitter disturb
the electrical equilibrium of the receiver, and are rendered
audible by the telephone.

The two capacity areas form what is practically a con-
denser. In order to increase the action the receiving
capacity may be kept oppositely charged to the transmitter
by means of a battery.

Edison. — A similar system of wireless telephony, which
has been used in communicating to moving railway trains,
was designed by Edison (Fig. 73). In this case one of
the capacity areas of Dolbear's system was replaced by a
wire supported on poles alongside the line, while the other
was represented by the metal roof of the railway carriage
which was connected to earth through a transformer and
the wheels of the car.

As receiver Edison used his electro-motograph telephone,
which depends on the variations in current due to the
alterations in friction between a rotating cylinder of wet
chalk and a palladium point attached to a membrane.

Collins. — From the somewhat incomplete notices which
have recently appeared, it seems that A. F. Collins has
carried out experiments of a similar nature.*

Collins used a microphone, which was placed in series
with the primary of a transformer and a microphone, one
end of the secondary of which was earthed, and the other
connected to an aerial wire. A Leyden jar was placed in
parallel with the terminals of the transformer. The receiver
consisted of a similar aerial wire, earthed through a trans-
former, while the other winding was connected to a tele-

* A. F. Collins, Electrical Review^ New York, xli., p. 742, 1902 ;
Electrical World, xxxix., p. 584, 1902, and xli., p. 1046, 1903 ; Scientific
American, Ixxxvii., p. 37, 1902.

INDUCTION TELEPHONY. 95

phone. Collins states that long electric waves were pro-
duced in the aerial of the transmitter, and were propagated
outwards through earth or water.

Collins' experiments were commenced in the end of
1899. In 1900 the distance attained was about 60 metres ;
later on, at Lake Rockland in New York State, this was
extended to about 5 km.

According to notices -in the American papers, Collins
has recently carried out further experiments in the North,
between Jersey City and New York.

Conversation was kept up between ships at a distance
of from 150 to 180 metres.

Although no practical results worth mentioning have
been attained with either earthed or unearthed electro-static
induction methods, they are interesting on account of the
employment of earthed aerial wires connected to capacity
areas which play so important a part in the methods of
wave-telephony described in the following section.

CHAPTER IX.

SPARK- TELEPHONY.

Imperfect Methods. — Soon after the publication of
Marconi's first experiments on telegraphy without wires
by means of electric waves, attempts were commenced on

I I I

Fig. 74.
Spark Telephone Transmitter.

Fig. 75.
Coherer Telephone Receiver.

all sides to devise a system of wave-telephony based on the
same principles. These essays consisted at first in merely
substituting a microphone for the interrupter on the coil

SPARK-TELEPHONY.

of the transmitting station (Fig. 74). The idea was that
on speaking into the microphone the current induced in
the transformer would cause a spark at the spark gap in
the aerial, producing oscillatory currents which would
transmit speech to a distance.

M B

VW\A

Fig. 76.
Series Arc and Spark Transmitter.

Any type of receiver could be used which was suitable
for telephonic reception of wireless telegraph signals, for
instance, a self-decohering coherer, microphonic contact,
electrolytic detector, or magnetic detector.

Numerous and often extremely complicated variations
of this simple transmitter are to be found in American and

WIRELESS TELEPHONY.

SPARK-TELEPHONY. 99

English patents and journals.* These improvements are
mostly concerned with the construction and arrangement
of the microphone, and the development of the secondary
oscillating circuit corresponding to that used in wireless
telegraphs. As examples may be taken Marconi's arrange-
ment with open oscillatory circuit, and Braun's with a
closed jig circuit coupled to the aerial.f A frequently
recurring modification is the replacement of the microphone
by an arc lamp in order that more energy may be trans-
formed in the induction coil circuit. J Some transmitters
of this type are shown in Figs. 76-78. Fig. 76 represents
Simon's arrangement of the speaking arc. Somewhat
similar connections are shown in Fig. jy^ except that the
speaking arc is placed in parallel with the primary of the
transformer instead of in series. In this shunt circuit a
condenser is placed to prevent the continuous current
traversing it. In Fig. 78 an arrangement is shown which
is based on Duddell's speaking arc connections.§ In both
of the latter systems the aerial is excited by a closed jig
circuit, unlike the simpler Marconi transmitter, which is
the basis of Fig. 76,

We must also notice a method in which the micro-
phonic current acts on the dynamo which supplies current
to the induction coil.||

We need not go more thoroughly into the methods of
this kind, since, though they are capable of transmitting a

* See also, for instance, F. J. M*Carty, San Francisco, U.S.A.,
patent C. 14,540, Class 21a, of 19th April 1906 ; German patent, No.
178,051 ; and French patent. No. 365,160, of loth April 1906.

t A short but important summary of these developments was given
by H. Th. Simon in the Phys. Zeitschrift^ iv., p. 364, 1903.

X See also H. Weselius, German patent. No. 176,010, of 28ih
February 1905, in which the variations of current are caused by
connecting one carbon of the arc to a membrane which vibrates with
the voice ; also French patent, No. 4,585, 1906.

j5 O. Nussbaumer, Phys, Zeitschr.y v., p. 796, 1904.

ll H. Mosler, German patent, M. 26,653, Class 21a 4, of 21st
December 1904.

lOO

WIRELESS TELEPHONY.

-oo-

SPARK-TELEPHONY.

lOI

musical tone, they give an extremely imperfect reproduc-
tion of speech. The reason for this is the impossibility of
obtaining a sufficiently rapid succession of sparks to give
the higher overtones by which the various vowels and
consonants are distinguished. A musical note, correspond-

v_y

Fig. 79.
Control by Light lonisation of the Spark Gap.

ing to the fundamental tone of the voice, is
transmitted, but all character of speech is lost.
If the spark length is diminished in order to
obtain the overtones, the discharge becomes an arc
and is inactive, producing no oscillations at all.*

Theoretical Desiderata.— The only method of getting

♦ See also R. Franz and J. Reinart, E.T.Z.^ xxv., p. 1,083, 1904,
and xxvi., p. 65, 1905 ; also W. Ruppin, E,T,Z.^ xxvi., p. 19, IQ05.

I02

WIRELESS TELEPHONY.

over this difficulty appears to lie in the employment of a
source of energy which is completely controlled by the
microphone current. This control may exist either in the
primary or secondary circuit of the transformer.* An
attempt in the latter direction was made by Lonardi in
1897, The sound vibrations were communicated to the

Fig. 80.
P^ssenden's Condenser Telephone.

balls of a Righi oscillator which were maintained at a
constant diflFerence of potential by means of an electrical
machine or otherwise. This method depends on the obser-
vation that the intensity of the emitted electrical waves
depends on the length of the spark.

* See Brown and Neilson, " Improvements in means of Tele-
graphing or Telephoning without Wires." British patent, No. 28,955,
1896. Completed 17th December 1896.

SPARK-TELEPHONY. 103

A Similar experiment belonging to the same class was
made by Jan Szczepanik.* Szczepanik used a spark gap
of constant length in series with which was a discharge tube
sensitive to light, like that used by Zickler in his experi-
ments on wireless telegraphy (Fig. 79). The cathode of
this tube was illuminated by a ray of light reflected from a
polished membrane on which the waves of sound were con-
centrated. The resistance of the discharge tube varies
with the intensity of the illumination, and the supply
current to the oscillator is correspondingly varied, hence
thq intensity of the emitted electrical waves varies with the
waves of sound. Heinicke's recently patented device for
the transmission of words and tones belongs to this class,
since he influences the spark directly by means of Rontgen
or cathode rays which are controlled by the waves of
sound.f

Other devices for causing alterations in the intensity of
the electrical waves which shall correspond with the sound
waves are based on the action of a microphone current on
the primary current in the transformer.J

Fessenden's Converters. — The principle of the second
group of methods consists in the variation of the frequency
of the electrical oscillations by influencing the capacity or
inductance of the oscillating circuit. In Figs. 80 and 81
are shown two arrangements of this kind devised by
Fessenden.

In the first of these the capacity of the air wire is altered
by the action of the sound waves on a condenser, one plate
of which is movable and vibrates in accordance with the
motions of the air. In the second, the inductance of the
aerial is altered by means of the primary of a transformer

* German patent, No. 138,226, of 9th May 1901.

t H. Heinicke, German patent. Application H, 39,706, Class 21a,
4th January 1907.

I See H. Mosler, German patent, M. 26,653, Class 21a 4, of 24th
December 1904 ; also Gernian patent. No. 173,690, of 15th July 1905.

I04

WIRELESS TELEPHONY.

put in series with the aerial, while the secondary is con-
nected to a microphone and battery (Fig. ^i).*

Rate of Sparking. — Although speech may doubtless
be transmitted by either of the above methods, the want
of a proper source of supply for the spark current is the
cause of great difficulty. If, for instance, one uses an

induction coil with an
interrupter only a re-
latively small number
of sparks occur per
second, and these
consist of intense but
rapidly damped oscil-
lations. In order to
make the conditions
clear we may suppose
that ^ turbine inter-
rupter is used which
breaks the primary
circuit IQO times per
second. Each break
causes an oscillatory
spark. The pitch of
sound given by the
series of sparks is
therefore lOO per
second.

Now, presuming

that a frequency of

a million per second,

such as is common in wireless telegraphy, is used, we

should have, if the spark were not damped, 10,000

* See the American patents. No. 706,742, of 6th June 1902, No.
706,747 and 753*863, both of 28th September 1901 ; and German
patent, No. i7i,535j of 13th August 1902.

Fig. 81.
Fessenden's Microphone Control.

SPARK-TELEPHONY. lOS

waves for each interruption. Since, however, there is a
rapid loss of energy in the circuit through radiation and
the production of heat, the current in a spark quickly
diminishes and dies out altogether after comparatively few
oscillations. This is shown in Fig. 82, which is an oscillo-
gram of the discharge of a condenser taken with a cathode
ray oscillograph. In this case the current died out after about
twenty oscillations. We therefore get only twenty oscilla-
tions instead of 10,000 at each discharge, and the discharge
itself lasts only the sj)hjjji of a second. Following it there

Fig. 82.
Oscillogram of Condenser Discharge.

is a relatively long pause of yj^ - imUff = TffljiJTT second
before another discharge commences. Fig. 83 gives a
diagrammatic representation of the successive discharges.
The distance between them is, however, much shortened
in the diagram, as that actually occurring in practice would
be fully 500 times as long as the discharge itself. Thus in
the figure the interval between the discharges, each repre-
sented by a length of 3 cm., would properly be shown as
15 metres.

Since, however, the frequency of the waves of speech
may amount to several thousand per second, it is clear

I06 WIRELESS TELEPHONY.

that a series of interrupted electrical oscillations in which
the pauses may be as long as yJtt of a second is entirely
unsuited to the transmission of speech. For this purpose
the individual discharges must follow one another very
much more rapidly ; the aerial must thus be excited by a
succession of sparks following one another so rapidly as

iSM i 3Li^ ^

Fig. 83.
Damped Wave Trains.

to give a note which is at least as high in pitch as the
highest overtones of the human voice, t'.e.y from three to
four thousand per second.*

In order to minimise the sound caused by the succession
of sparks the rapidity must be further increased, so that
the spark frequency rises beyond the limits of audibility.

* The highest audible tone has a frequency of about 33,000 per
second, but a pitch of above 4,000 per second is not of common
occurrence.

CHAPTER X.

ACCELERATED SPARK RATES,

Majorana's Spark Method. — Q. Majorana carried out,
in the Physical Institute of the University of Rome, the
first successful experiments in the use of a spark rate of
above 10,000 per second.*

Variable Spark Gap. — The conversion of speech into
electric surges was in this case by Lonardi's method of a
variable spark gap. For this purpose a moving stream of
mercury was used as one electrode, the other being fixed.
The microphone current acted on the mercury column,
bringing it nearer to, or further from, the fixed electrode,
thus altering the intensity of the sparks in accordance with
the sound waves.

By using a magnetic detector Majorana obtained an
intelligible reproduction of the transmitted speech. The
transmitting aerial was outside the building of the Physical
Institute, while a wire of about I metre in length inside the
building served as receiving aerial. Majorana believed that
by using longer aerials with his apparatus he would be
able to transmit speech several kilometres. This arrange-
ment had the disadvantage that after a short time the
mercury became so much altered by the discharge that it
was no longer fit to use ; Majorana, therefore, endeavoured
to replace it by a high-tension microphone placed directly
between the aerial and the spark gap. Since the intensity

* Nuovo CimentOy 1904 ; The Electrician^ 7th October 1904 ;
E,T.Z.y XXV., p. 943, 1904 ; Eclair Elecir.^ xliii., p. 65, 1905.

I08 WIRELESS TELEPHONY.

of the radiation depends on the resistance of the aerial wire,
it is clear that it must be altered by the variations of the
resistance of the microphone.* Majorana has recently
communicated to the Italian Electrotechnical Society a
description of his high-tension microphone, and of the
results obtained with itf In this paper he bases his ex-
planation of the action of his hydrodynamic microphone on
the principle of the hydraulic telephone. The apparatus
consists essentially of an electrically conductive stream of
liquid whose movements are influenced by the sounds
of speech. The stream falls upon the plane surface of the
so-called "collector,** which consists of two cylindrical
pieces of platinum insulated from one another. On strik-
ing the upper surface of the collector, the fluid spreads out
over the surface, and connects electrically the two halves of
the collector. The jet of fluid is controlled by the action
of the voice on a diaphragm forming one side of the tube
through which the liquid flows, more or less flowing out in
accordance with the waves of sound. The film of liquid
connecting the plates of the collector thus varies in thick-
ness, and hence in conductance, and therefore if the plates
are connected by proper means to a spark gap, the current
will vary simultaneously, producing an electrical vibration
corresponding exactly with the sound waves.

Majorana's Rapid Sparking. — Before we leave these
researches we must describe more completely the method
by which Majorana obtained so high a rate of sparking as
10,000 discharges per second. The only information given
on the subject is that the supply current was taken from
the town mains (alternating at forty periods per second),
and was passed through the primary of a transformer. On
superficial consideration it might be supposed that a trans-

* Experiments were recently made (8th April 1907) with this
apparatus between the Telegraph Institute and the Wireless Tele-
j^raph Station on Monte Mario, in Rome.

t Ekitricista^ pp. 213-215, 1907.

ACCELERATED SPARK RATES.

109

former supplied in this manner would (as in the case of an
interrupted unidirectional current) only give eighty sparks
per second,* and that the production of 10,000 per second

would require an alternating current of 5,000 periods per

* In the resonance induction coils now used in wireless telegraphy
the rate of sparking in the secondary is much greater than that in
primary circuit.

no WIRELESS TELEPHONY.

second. This is no doubt usually true.* Thus when we
examine Fig. 84 we see that the first discharge takes place
at the moment when the potential rises sufficiently to cause
a spark ; a moment which may naturally occur before the
secondary voltage has reached its maximum. This point
is marked A on the curve, and represents the potential
which just causes a discharge across the spark gap. As
the supply of energy to the primary continues, this spark
becomes an arc, which is extinguished when the induced
voltage is no longer sufficient to maintain it. This potential,
at the moment when the arc breaks, is represented by the
point B on the curve, and is considerably lower than that at
which the discharge commenced. In this case, therefore,
there is in each alternation a considerable period during
which an arc exists. This is represented by the shaded
portion of the diagram between A and B. Since there can
be no oscillatory discharges while this arc continues, they
only occur at the moment when it is broken (B on curve), and
as the potential is then low they are not energetic. We see,
therefore, that for each alternation of the primary current
only one train of waves is produced by the secondary
(Fig. 85). If, however, a choking coil of considerable in-
ductance is put in the supply circuit, the conditions are
altered, and a large number of secondary discharges may
be obtained for every alternation of the primary current,
particularly when the discharge voltage is kept relatively
low by the use of a short spark gap.f The moment the

♦ Alternating currents of such frequencies are, of course, most
suitable for wireless telephony. Fessenden has recently published the
results of his experiments in 1903-04, in which he used an alternating
current generator giving 10,000 periods per second (see Zeitschrifi
fiir Schwachstrom Technik^ i., pp. 74 and 93, 1907). Similar attempts
to attain a high discharge rate by means of a singing arc will be
described later.

t See also the following : — H. Abraham, Soc, Franc, de Phys.^
5 Mai 1899, Bulletin, p. 70 ; A. Blondel, British patent, No. 21,909, of
3rd December 1900 ; J. Harden, Pkys, Zeitsckr,^ iv., p. 461, 1903 ; also
F. J. Koch, Ann. d, Phys.^ iv., 14, pp. 547-555, 1904.

ACCELERATED SPARK RATES.

Ill

spark commences (point A on Fig. 86) the total primary
voltage comes on the choking coil, and the supply current
suddenly falls, and energy is no longer forthcoming for the
maintenance of the arc. When the arc has been extinguished
the voltage again divides itself between the choking coil

and the primary of the transformer, and hence, as the
primary voltage continues to increase, the induced secondary
voltage may again rise sufficiently to cause a spark. The
action then repeats itself. The self-induction of the trans-
former diminishes, the primary current suddenly rises, the

112 WIRELESS TELEPHONY.

choking coil begins to act and checks the supply of energy
so suddenly that the second arc also breaks. Spark after
spark thus follows, and all tHe more rapidly as the primary
voltage nears its maximum, but after this has been passed
the intervals between them increase until the point B on
the curve has been reached, when they leave off until after
the commencement of the next alternation. A large number
of discharges is therefore obtained at every alternation by
aid of the choking coil, every one of which gives a jig
suitable for transmission. This is shown in Fig. 87. In
Figs. 88 and 89 are given cinematographic pictures of the

Fig. 88.
Spark Groups following one another.

discharges of a large transformer. In these one can see
clearly that there are several sparks during each alternation,
and that they are more numerous with a short than with a
long spark gap. F'ig. 88 with a long spark shows only two
or three per alternation, while Fig. 89 with a shorter gap
shows about twenty-five.

In order to show that each group of sparks actually
represents an alternation, two parallel spark gaps were
arranged, the electrodes being a plate and a point or a
point and a plate. The gaps were so placed that their
images on a photographic plate came side by side (Fig.

ACCELERATED SPARK RATES. II3

90). By this means the sparks were divided into positive
and negative groups as shown in Fig. 91, on account of
the greater facility with which a positive discharge com-
mences at a point. Each spark consists, of course, of
several oscillations, but these are too rapid to show on a
plate driven at the speed used in these experiments. In
order to obtain as many sparks per second as possible, the
gap must either be decreased or the voltage raised. Of
course there is a limit to this procedure, as otherwise the
oscillations may become too weak, or the sparks may run
into one another and become an arc which is inactive.
The latter difficulty may be to some extent overcome by

Fig. 89.
Higher Rates of Sparking.

using electrodes of the so-called non-arcing metals alu-
minium or zinc, or by Thomson's method of using a
magnetic or air blast, which breaks the arc and produces
the required oscillatory discharge at the moment of rupture.
On the other hand, Majorana used a stream of air or car-
bonic acid which played upon the spark gap, " in order to
maintain the regularity of the discharge," as he puts it in
his paper on the research.

There still remain two other factors which influence the
number of discharges which it is possible to obtain during
an alternation, namely, the inductance and capacity of the
secondary system. The less the inductance and capacity
of the conductors connected to any given oscillator, the

114

WIRELESS TELEPHONY.

greater is the number of discharges obtainable per second,
and similarly, if the capacity and inductance of an oscillator
be reduced, the rate of sparking will be increased.

Since, however, Thomson^s (Kelvin's) fundamental law
of wave-telegraphy gives the frequency of the waves in
terms of the capacity and inductance, it is as a rule best to
consider the dimensions of the oscillator as given, and to

choose a transformer with as small
a secondary capacity and induct-
ance as possible. The law re-
ferred to is given in the formula

^' ^ /, p ^ where C is the capacity,

L the inductance, and n the
number of oscillations per second
(the frequency).* The wave-
length A. IS determinable from

this by the formula A = ^

metres. The influence of the
dimensions of the secondary wind-
ing is well shown in the following
examples. The greatest rate of
// \\ sparking obtainable with the trans-

/ / \ \ former used for producing the

/ / \ \ sparks shown in Figs. 88-91 was

•i-w *»t-^ about 60 per alternation ; its

, , ™^^'* ^* , . . . secondary consisted of a very

Method of Photographing Posi- , , - . ,. 1.1

tive and Negative Sparks l^rge number of windmgs, and had
for Fig. 91. therefore great capacity and induct-

ance. With an alternating current
transformer designed to give about 3,000 volts, and having
a much smaller secondary winding, fully 200 discharges per
alternation were obtainable. Supposing, therefore, that
each discharge lasted say the TiyiiVoiy of sl second, and con-

♦ W. Thomson, PM. Mag,, (4) v., p. 393, 1853.

ACCELERATED SPARK RATES.

tained ten oscillations, we find that in tott second, namely,
the duration of an alternation, the oscillations occupy
sijf second, so that the time covered by active oscillations
would be to blank time in the ratio of 1:4, if the dis-

FiG. 91.
Positive and Negative Altemale Spark Group.-.

charges were uniformly distributed throughout an alterna-
tion ; this, however, is not exactly the case, as we have seen
above.

Mercury Vapour Spark Gap. — We shall next notice

Il6 WIRELESS TELEPHONY.

shortly the corresponding observations when a mercury
vapour lamp is employed as spark gap.

If instead of the ordinary spark gap in air we employ a
mercury vapour lamp at the proper pressure, there is a
marked increase in the potential without any corresponding
increase in the damping ; it is therefore possible to excite
more powerful oscillations. In addition to these, there is
the advantage that on account of the very rapid variations
of the resistance of the mercury vapour, there is less
tendency to the formation of an arc. Hence the dis-
charges may be made to follow one another with greater
rapidity than in air. The interrupter action of a mercury
lamp supplied by a high tension alternating current was
first observed by Hewitt* Investigations of this subject
have also been made by Simon and Reich,f and W.
Pierce.J

The last of these photographed the discharge by means
of a swinging lens on a rotating film. The best vapour
pressure for a potential of 15,000 volts was found to be
0.02 mm. By using a small Leyden jar in parallel
with a similar vacuum tube, Pierce obtained 200 dis-
chargeSjg each consisting of several oscillations, during an

* Cooper Hewitt, Elec, Review^ New York, xlii., No. 8, of 21st
February 1903.

t H. Th. Simon and M. Reich, Phys, Zeitschr., iv., pp. 364-372,
1903 ; and H. Th. Simon, lecture to the Scientific Congress at
Cassel on 22nd September 1903, for which see Phys. Zeitschr.^ iv., pp.

737-741, 1903.

X W. Pierce, Phys. Zeiischr.^ v., pp. 426-437, 1904.

§ In order to complete our account of this part of the subject we
must take note of some recent patents in which a high tension current
is used with a vacuum spark gap for the production of the oscillatory
discharges used in wireless telegraphy and telephony. The Gesell-
schaft fiir drahtlose Telegraphie, of Berlin, has patented a device for
producing very slightly damped oscillations, in which a condenser of
large capacity is connected in parallel with the secondary of the
mercury lamp transformer. The lamp itself forms the spark gap of
an oscillating circuit with capacity and inductance which is connected

ACCELERATED SPARK RATES. II7

alternation lasting xj^r of sl second, so that the pause between
successive sparks was only yinnnnr of a second. Each dis-
charge was regular and sharply defined, which showed that
even at this discharge rate there was no lowering of the
potential by the formation of conducting vapour.

directly or inductively to the aerial (German patent, No. 160,990, of
14th April 1905). In order to increase the amplitude of the dis-
charges Eisenstein concentrates the entire energy of each alternation
into a relatively short time by using proper means for connecting the
vacuum tube only during these moments to the alternator. (German
patents, E. 11,332, Class 21^1 4, of 5th December 1905, complete
patent, 182,656, and E. Class 21a 4, of 3rd February 1906, complete
No. 182,657 ; also French patent, No. 368,988, of 17th August 1906.)

CHAPTER XI.

MULTIPHASE SPARK DISCHARGES.

Imperfections of Spark Method. — It is therefore clear
that a large number of discharges per second, each of which
gives rise to an oscillatory damped current, may be obtained
from an alternating current of ordinary frequency. Although
it is possible by this method to obtain a sufficient discharge
rate for the transmission of speech, as Majorana*s experi-
ments proved, it has still the disadvantage that in the
neighbourhood of the zero of potential in each alternation
there is a somewhat long pause, and that in general the
discharges do not follow one another with anything like
uniformity. These pauses, occurring at every reversal,
disturb the transmission of speech very considerably, as
the author observed in a research undertaken, independently
of Majorana, in the winter 1904-5. A microphone was
used to influence the supply current to the primary of an
alternating current transformer.* The transmitted speech
received on microphonic contact and telephone was rough
and broken like that of a stammerer.

The gaps in the series of discharges, which occur when
an ordinary sinusoidal alternating current is used, may be,
to a considerable extent, filled up either by Blondel's

♦ In these experiments the microphone was connected in parallel
with a coil as used by Nussbaumer {Phys, Zeitschr.^ v., p. 796, 1904).
An inductive coupling may be used in place of a direct one (Mosler,
German patent, No. 173,690). Direct action on the dynamo is
described in Mosler's application, M. 26,653, Class 2\a 4, of 24th
December 1904.

MULTIPHASE SPARK DISCHARGES.

119

method* of using an alternating current of nearly rect-
angular curve, or by Eisenstein'sf method of employing a

KiG. 92.
Blondel's Method of Increasing Spark Rate and obtaining more Uniform
*• Succession of Sparks.

multiphase current. As is shown clearly in Fig. 93, it is
possible by a proper arrangement of the spark gaps to
make the discharges in one or other of the phases to follow

Fig. 93.

Three- Phase Current for obtaining Continuous Succession of Spark

Discharges.

one another practically continuously, and thus obtain a

* See German patent. No. 159,330, of 17th August 1902, and British
patent, No. 15,527, of i ith July 1902.

t See German patents, No. 175,438, of 9th July 1905, and No.
176,011, of 1st February 1906.

I20

WIRELESS TELEPHONY.

continuously active transmitter. The simplest connections
for this purpose are shown in Fig. 94, in which it will be
seen that the transmitter consists of three similar parts.
Each spark gap, F, is connected to a transformer, j, and
the primaries of these are in a star connection. In this

Fig. 94.
Triple Inductorium for Three- Phase Current, with Spark Gaps in Aerials.

arrangement each phase actuates practically a complete
transmitter. An arrangement with only one aerial wire
is shown in Fig. 95. In this case the three oscillating
circuits contain a common inductance which also forms
part of the aerial, an arrangement also recognisable in

MULTIPHASE SPARK DISCHARGES.

121

Eisenstein's apparatus shown in Fig. 96. A mesh con-
nection may, of course, be used instead of the star. Fig.

Fig. 95.
Three- Phase Transmitter with Continuous Single Aerial.

97 shows a transmitter of this type. Here the terminals of
the supply circuits are connected to the primaries of the

122

WIRELESS TELEPHONY.

main transformers in pairs, while all their secondaries are
in series, and a third circuit, containing condensers and
transformers with a three-cornered spark gap, forms the

Fig. 96.
Three-phase Transmitter.

oscillator, and is coupled to the aerial wire by the secondaries
of these subsidiary transformers. The action of all the
spark gaps must be alike in order that the discharges may

MULTIPHASE SPARK DISCHARGES.

123

correspond exactly to the phases of the main current.
Thus waves of the same length will be radiated from the
aerial whichever of the spark gaps may at the moment be

Fig. 97.
Three-Phase Transmitter, Mesh Connection.

acting. In this manner a continuously excited transmitter
has been realised in practice.

Instead of a three-cornered spark gap, three separate

124 WIRELESS TELEPHONY.

gaps in star connection may be used along with capacities

in mesh connection.

Although in the above-described method of Eisenstein's

there are no long pauses between discharges, there remain

nevertheless the minor irregularities which become more

and more noticeable with every increase of the voltage.

This difficulty is clearly only surmountable by the use of

a high tension continuous current

A thorough investigation of this method has been made

by Simon and Reich, who employed as exciting circuit of

the transmitter a Braun*s oscillator.*

They used as source of current a high tension dynamo,t

or a battery of 5,000
volts. The secondary
coil of a 40 cm. spark
induction coil was
used as inductance
in the leads to the
Leyden jar.

A continuous and

Mercury VapouVLamp as Spark Gap. steady excitation was

obtained with a mer-
cury lamp as spark gap. J The rate of sparking in-
creased as the voltage was augmented, as in the case of
alternating current, and remained constant as long as the
voltage was not varied. If an ordinary air gap was used
energetic oscillations occurred at the commencement, but
were immediately succeeded by an inactive arc. It is only
possible to obtain a continuously active discharge when
the pauses between the sparks are increased by the inter-
position of a considerable inductance.

* H. Th. Simon and M. Reich, Phys, Zeitschr.^ iv., p. 364, 1903,
and H. Th. Simon, lecture at the 75th Scientific Congress at Cassel
on 22nd September 1903, Phys, Zeiischr.^ iv., p. 737, 1903.

t This machine (20 PS.) was supplied by Messrs Schuckert & Co.,
of Niimberg. It was model Z. H. 20, 5,000 volts, 3 amperes.

t See also German patent, No. 153,792, of 18th January 1903.

MULTIPHASE SPARK DISCHARGES.

125

Simon's Theory. — The fact that the spark becomes
inactive must thus be attributed to the pauses between the
sparks being not sufficiently long to permit of the spark
gap losing its conductivity by cooling. In the papers
quoted Simon gives a quantitive discussion, which gives
a most satisfactory confirmation of his experimental results
and establishes many important points in the theory of the
production of undamped oscillations. We shall therefore

rO'^dffconds

Fig. 99.
Charging Curves of an Oscillating Circuit.

give a short abstract of his investigation before proceeding
further.

If a capacity C be suddenly connected at the moment
/=o to a source of constant potential E, its potential e at
any time / thereafter is determinable by means of the
equation —

" " if E

^/2 "L^dt LoC

where R^ is the resistance and L^ the inductance of the

126 WIRELESS TELEPHONY.

circuit. The integral of this equation taken between the
proper limits is —

e = E - 2E ^^C ^ ^-RpZ/aLo

sin

( 2L0C RoC j

If R^^C^ is negligible in comparison with 4L0C, and if,
also, the lag in phase is nearly Tr/2, we get approximately —

Taking into account the constants R^, L^, and C of his
apparatus, Simon calculated the charging curves for various
steady voltages* given in Fig. 99.

The time of discharge of the condenser, reckoned till
a new discharge commences, is determined by the point
of intersection of a line drawn parallel to the axis of
time at a height V, with the e curve. In Simon's experi-
ments this time was of the order of a thousandth of a
second.

We may discuss in a similar way the discharge which
takes place across the spark gap at every spark. We
have —

^ 2E s/LC ^ . R,/,L cos n/4^^"- ^'^'
x/4LC - R2C2 * 2LC

where R is the resistance and L the inductance of the
oscillating circuit.

• The corresponding current is given by —

i = ^ ^ - Ro^/Lo . ^

vloTc'-^' -^^"^^ur

and is shown by a broken line in Fig. 99.

Also neglecting the damping factor c ~ ^o'/^o we get ^ = o for / = o,
or 2t VLqC, 4t a/LqC, &c., and otherwise is always positive. / — o,
for / = o, or IT \/LoC or 2t x/LqC, &c., and is sometimes positive and
sometimes negative in the intervals. The limiting value* of ^ is 2E ; '
and of / is E/ \/Lo/C.

MULTIPHASE SPARK DISCHARGES. 12/

Under the same restriction as before, namely that R^C-
is negligible* in comparison with 4LC, we obtain —

tf - E. €-R'/=»L. cos ,L-
s/lC

i.e.j a damped oscillation with the period T = -=27r^CL,

where u is the frequency. The damping is determined by
the factor € - ^'^^^ and the logarithmic decrement —

s = ^J = ^ .

2L 2L//

The period of the oscillations which take place at each
discharge is naturally much less than that of the charging
current since R and L are very much less than Rq and Lq.
In Simon's experiments they run from about a hundred-
thousandth of a second to a millionth.

The damping is somewhat considerable, particularly, as
M. Wien has shown,t if Braun's form of circuit be used.

If one takes ten complete oscillations as the limit in
which the potential will be so far run down that the spark
is no longer maintained, one finds that the duration of
the discharge in Simon's experiments is only from a ten-
thousandth to a hundred-thousandth of a second, and is
therefore much less than the time of charging.

From the formula given above for the variation of the
condenser voltage during charging, we obtain mathemati-
cally several results of importance which we have already
established experimentally. Thus we see that for any given
condenser the pauses between successive discharges are
smaller the greater the voltage E of the source of electricity,
and the less the discharge voltage V, or the length of the
spark gap. For a given supply voltage E they are shorter
in proportion as V and C are less ; and finally, for a given

* If thi^ condition is not fulfilled, as in the case of a long spark
gap, the discharge becomes continuous, or rather aperiodic.
t M. Wien, Ann. d. Phys,^ viii., p. 686, 1902.

128 WIRELESS TELEPHONY.

discharge voltage V, they decrease in proportion to the
capacity C, and inversely as the supply voltage E.

With an alternating current supply we obtain, as we
have already shown, a periodic series of unequal pauses
which remain the same as long as the spark gap and
capacity are kept constant.

Finally, it should be noticed that it is not always
necessary that the stationary voltage of the supply current
should be as great as that required for the spark, since in
consequence of the oscillatory character of the charging, it
is obvious that the potential at the condenser reaches a
maximum during the first swing which is nearly twice as
great as that of the supply (see Fig. 59, and footnote,
p. 126).

We see, therefore, that with given capacity and spark
length the number of discharges per second may be in-
creased by increasing the potential of the supply up to a
certain limit, which is defined by the condition that the
heat liberated in each spark must be so small that the air
has time to cool before the next commences. Otherwise
an inactive steady arc is produced, or at best one in which
the current varies over a small range only, as in Duddells
phenomenon. Without doubt this type of wave producer,
which is capable of sending out a very large number of jigs *
per second, would have proved very useful in wave-tele-
phony if the still more advantageous properties of the
unstable arc had not been discovered.f

* "Jig" denotes a damped train of electrical oscillations of the
order of frequency used in wireless telegraphy and telephony (inrca one
million per second).

t R. A. Fessenden has recently published a description of his
experiments carried out during the years 1900-4. Among other
arrangements he used a rotating spark gap supplied with constant
current at 5,000 volts ; with 500 revolutions per second 20,000 sparks
were obtained per second. Speech was transmitted, but the noise due
to the sparks was disturbing {Zeitsckr. fiir Schwackstromtechnik^ p. 72,
&c., 1907 ; see also Appendix).

MULTIPHASE SPARK DISCHARGES.

129

Electrical Quantities Controlled by Sound— The

electrical discharge system maybe influenced by the sound
waves either as regards the intensity or frequency of the
electrical oscillations in the transmitter or aerial wire,
whether by action on the supply circuit, the secondary
circuit, or the aerial itself. The operation may also be
accomplished by a control of the rate of sparking, in which
case the transmitter is not continuously excited, but acts
only when influenced by the sound waves ; it is therefore
at rest when no sound is being communicated to it.

As an example we may take an arrangement of
Blondel's, in which the supply
circuit, or the oscillating cir-
cuit itself, is interrupted by
means of a manometric
flame.* In the apparatus
shown in Fig. 100, the voltage
is chosen so that it is not suf-
ficient, when the flame is at
rest, to cause a spark. When,
however, the flame commences
to move up and down, the
spark, which is supplied by an
alternating current of the form
shown in Fig. 92, jumps the
gap and excites the transmitter. The action is due to the
variations in resistance caused by the extension of the flame
between the electrodes, and is, of course, synchronous with
the sound waves.

Any of the detectors mentioned in the earlier part of
this section may be used as receiver in connection with a
telephone in the local circuit, or the oscillatory currents in
the receiving circuit may even be made to act directly on
a membrane. If the latter consists of metal it may be

Fig. icx).

Blondel's Manometric Flame

Controller.

♦ See British patent, No. 15,527, of nth July 1902, and German
patent, No. 160,880, of 17th August 1902.

130

WIRELESS TELEPHONY.

placed near a solenoid containing only a few turns, in which
case the Foucault currents induced in it cause it to vibrate *
A condenser may be connected in series or parallel for
tuning purposes.

Damped and Undamped Waves. — The foregoing
methods depend on the work of Feddersen and Hertz. A
comparatively slow charging is followed by a sudden and
oscillatory discharge, which rapidly dies out, leaving the

spark gap again in a
non-conducting condi-
tion. The whole pro-
cess may be compared
to the discharge of a
machine gun, ix,, to a
succession of impulses
of great activity alter-
nating with moments of
entire inactivity. It is
clear that a method of
producing a continuous
stream of waves like the
sound of an organ pipe
would be an immense
advance on this system,
and would open up the
possibility of a wireless telephony far more perfect than
could be attained by these earlier methods.

Figs. loi and 102 show diagrammatically the differ-
ence between damped and undamped waves. In the former
the successive amplitudes of the waves decrease, in the latter
they are constant.

Fig. ioi.
Damped Oscillations.

Fig. 102
Uniform Oscillations.

• See Fessenden, American patent, No. 706,747, of 28th September
1901, and German patent. No. 171,535, of 13th August 1902; also
Blondel, British patent, No. 15,527, of nth July 1902. See also
Appendix.

CHAPTER XII.

HIGH FREQUENCY ALTERNATORS.

High Frequency Alternating Currents. — Many experi-
ments have been made with the object of producing a series
of waves of constant amplitude, in order that sharp tuning
may be obtained.*

An attempt has been made to solve the problem in a
purely mechanical manner^ by the construction of high
frequency alternating current generators, the first machine
of this type being described by Nicola Tesla in his book
on " Researches on Multiphase Currents, and on the Alter-
nating Currents of High Voltage and Frequency " (Halle,

189s).

A tabular statement of the machines of this character
which have been constructed, recently given by Rauten-
krantz, is reproduced below, t

As may be seen from the following table, machines
have already been constructed which produce alternating
currents of sufficiently great frequency for wave telegraphy
or telephony ; the amount of energy given out is, however,
so far, exceedingly small.

* On electrical oscillations and oscillators, see C. Heinke, Handduch
der Electro tecknik^ Bd. i., pp. 43-55, 1904.

t Annalen der Electrotechnik^ i., pp. 617-620, 1906. See also
Appendix.

132

WIRELESS TELEPHONY.

CO >*

III

I«i laajajoinaiTQ

stiopniOAa^

O
vn

00 h

13^

^ 5

^.S c

S p«^ o g 5

a; -» «
Is.? C

^ >s * OT O

>- 5 « 00 p
• 2 o

C bo!
o «

C X t')

*- i3

S3 O 2

'to
c

p 'J 'In

S>§

•J
o
u

HIGH FREQUENCY ALTERNATORS.

133

^i.?

f«

>•

kj J '^

vSoo

•0

If'

ca -:

S» X

Id.

•^

■^

«2

•5

§§ I

«r

^8* -

00*

iviiuaiajmnaiio

CO to

iacf

§1 1

•oopniOA^H

i| III

."2

Sm3

s S 4!
g u «

-^1

5 tt!

4) C g

55.2

i^ Sdfeg

•

u w K , ^ ^

3 =

■|J

>M —

C/5

U UJ

134

WIRELESS TELEPHONY.

S o S a

c c

1 .l^^^

L^ll^l^.^o:.^

£•5 cL^^ -02::

00 ^

8 i

O
Ed

O
>

X
o

'oas isd *ai
pniu9jajinnaii3

Oj to bfiV

• (A

!•£ c

^ SJ 3 o

co.X,

UTS N TS

IK s
2 <J c4

it G
C O

4. ^"5

3.S2

no 13

fe 2 u

♦5 bo :>.

•g iJ >

*•* «i ti

Ji § 8

C OS rt

rt-fS (A

<M o (O

4) A) O

•n i-i "-^ v> • r* «« e

rt boo "^

4-* r* {/I ^N

3 CO

N « «;

5 4> »v. ^^ a
.^^ =^ .

•J

Q
Q

HIGH FREQUENCY ALTERNATORS. 1 35

H.P. of Spark Discharge. — M. Wien has, for instance,
estimated the output during one discharge of a closely
coupled Braun's oscillator at 1955 H.P. A very great
advance in the construction of high frequency alternators
will have to be made before there is any possibility of
transmitting energy at so great a rate as this by their
means, though the fact that the receiving circuit may be
dimensioned so that it may revibrate to the received
waves renders transmission possible with very much
smaller currents if they are sustained instead of only
momentary.*

There is no doubt that in the course of time these
difficulties will be got over, and it seems to the author that
these or similar methods of producing a high frequency
current mechanically and without the use of a condenser
have a most promising future in wireless telegraphy and
even more so in telephony.f

High Frequency Alternators. — The current produced
by the high frequency alternator is applied by one of the
known methods to the excitation of the aerial, a close
coupling being generally used for this purpose. The
conditions for resonance may be fulfilled by a proper choice
of capacity and inductance, an extra capacity being in
certain cases introduced into the alternator circuit. J

For revibration (resonance) we must have : —

27r«L - — 7^
tan <^ = ^ = O; i.e., 27r«L - ^^^ = O,

♦ M. Wien, Ann. d. Phys., viii., 686, 1902.

t SGtZeiischr,furSchwackstromtechn,^\.^'!^, 114, 1907, for descrip-
tion of Fessenden's Condenser-Dynamo; also see Riidenberg,
German patent. No. 179,954, of 22nd October 1905 ; also patent
specification, R. 24,609, 21^, of 3rd June 1907 (published nth July
1907), and "A Method of Producing Alternate Currents of Any
Frequency,'* Phys. Zeitschr.y 8, p. 668, 1907.

X See also British patent. No. 17,708, of 1902, and Erich Vossnack,
German patent. No. 184,385, of 29th November 1905.

136
or

WIRELESS TELEPHONY.

n =

■VlC

ue.y the impressed frequency = the natural frequency of
the circuit.

The wireless telephonic transmitters which we are now
considering differ from those of the spark-telephony type
in the absence of a spark gap in the oscillating circuit.

Fig. 103.

Ruhmer's High Frequency Alternator Controlled by Induction between

Microphone and Field-Magnet Circuits.

The conversion of the sound waves may of course take
place in any of the ways already described, and may
depend on the variation of either the intensity or frequency
of the oscillations. In both groups of methods the trans-
mission of speech is by means of varying electrical waves,
in the first case with constant, and in the second with vary-

HIGH FREQUENCY ALTERNATORS.

137

ing frequency, which act with varying intensity on the
detector in the receiving circuit and thus reproduce the
corresponding sounds in the telephone attached to it.

When a constant wave-length is used the variations of
the intensity produce similar variations in the receiver,
while if transmission depends on variation of the wave-
length, the receiver must be a persistent oscillator which
only' responds when acted upon by waves which are of its
own natural frequency, and falls out of resonance when the
frequency of the im-
pressed waves varies. ir-

The author's attempt*
to influence the exciting
current of a high fre-
quency alternator by
means of a microphone
belongs to the first group
(see Fig. 103). This
group is also perfectly
analogous to the method
of light -telephony de-
scribed in the first sec-
tion of the book.

Fig. 104.

The Effects of Variation of Coupling

on Revibration.

Resonance Curves.

— Simon and Reich's t
transmitter for wireless telegraphy and telephony depends
on the variation of the intensity of the radiation by altera-
tion of the closeness of the coupling between the high
frequency circuit and the aerial wire. Let curve i in Fig.
104 represent the resonance curve for any given coupling,

♦ German patent application, R. 19,015, Class 21a 4, of 14th
December 1903, which, however, was refused. Fessenden has
recently repeated the attempt, American patent, No. 793,649, of 30th
March 1905. Electrical World and Enjs^ineer^ xlvi., p. 90, 1905 ; The
Electrician^ Iv., p. 795, 1905 ; and E.T.Z,^ xxvi., p. 950, 1905.

t German patent. No. 146,764, of 8th October 1902 (lapsed).

138

WIRELESS TELEPHONY.

the abscissae being the ratio of the natural periods of oscil-
lation of the aerial and of the primary circuit, and the
ordinates the amplitudes of the corresponding oscillations
in the aerial. Curve 2 represents the conditions with a
different coupling.

By varying the strength of the coupling one goes from
the ordinate i^ of the first curve to the
corresponding ordinate i^ of the second
curve, while the abscissa remains constant,
/>., without alteration of the ratio of the
frequencies of the aerial and primary circuit.
It is clearly best to work with as perfect
\^l bsi resonance as possible, a condition indicated
by' the maximum ordinate.

According to Simon and Reich the
desired variation of the inductive coupling
between the aerial wire and the primary
system may be achieved by the use of an
iron diaphragm forming part of the ^mag-
netic circuit of the transformer. The
^>. action of the sound waves on the mem-

\^J brane causes corresponding variations in

^ the energy supplied inductively to the

aerial. With direct coupling the strength
may be altered by motion of the point of
connection on the primary system.
Et

Fessenden's Transmitters. — We shall
close our remarks on this class of trans-
mitter with a description of one of Fes-
senden's wireless telephones.*
Fessenden places the high frequency alternator, which
must have an armature of low resistance, directly in the

Fig. 105.
Fessenden's Micro-
phone Transmitter

in Aerial.

* American patents, No. 706,742, of 6th June 1902, No. 706,747
and No. 753,863, of 28th September 1901. See also German patents,
No. 143,386 and No. 171,535, both of 13th August 1902.

HIGH FREQUENCY ALTERNATORS.

139

a
o

I40

WIRELESS TELEPHONY.

earthed aerial wire, and by proper adjustments of capacity
and inductance makes the natural period of the latter the
same as that of the alternator current.

One of Fessenden's transmitters belongs to the first
group, in which transmission is effected by variation of the
intensity of the radiated waves. A microphone is inserted

between the aerial and
earth wires (Fig. 105).
The variations of the re-
sistance of the micro-
phonic contact produced
by the sound waves cause
synchronous alterations
in the current in the aerial,
and therefore in the
energy radiated.*

In another of Fessen-
den's senders the control
of the radiation is effected
by alteration of the fre-
quency through variation
of the inductance or
capacity of the aerial
system. Unlike Simon
or Reich's arrangement, however, there is in this case an
alteration of the ratio of the frequencies of the aerial and
primary circuits, so that the conditions are represented
by Fig. 106 and not by Fig. 104. In this method of

Effect of Variation of Frequency on
Revibration.

♦ American patents, No. 706,742, of 6th June 1902, No. 706,747
and No. 753,^63, of 28th September 1901. See also German patents,
No. 143,386 and No. I7i,535) of 13th August 1902.

With an arrangement of this kind Fessenden carried out experi-
ments between his Brant Rock station and a steamer, on 21st
December 1906, the range being up to 16 km. Communication was
also carried on with Plymouth, Mass. At the land station an alter-
nator built according to the American patent, No. 706,737, of 29th May
1 90 1, giving 80,000 cycles per second, was used. The resistance of

HIGH FREQUENCV ALTERNATORS. I4I

control the variation is from a given value of the abscissa a,
i.e., of the ratio of the natural frequencies of the primary
and aerial, to another, b, and hence the amplitude of the
oscillation in the aerial falls from i^ to i^

the armature was about 6 ohms, and it ran at 10,000 revolutions per
minute. The output was only 50 watts. The receiving station had
an aerial wire 21 metres high. An electrolytic cell was used as
receiver. See Scientific American, xix., January 1907 ; Zeitschr, fUr
Electrotechn, und Maschinenb.^ xxv., p. 183, 1907; E,T,Z,, xxviii.,
p. 299, 1907 ; and Zeitschr, fUr Schwackstromtechn,, i., pp. 72, 93, and
114,1907. See also Appendix.

CHAPTER XIII.

THE ARC AS HIGH FREQUENCY '
GENERATOR.

Although the methods in which an alternate current
generator of high frequency is used directly are of great
promise, the problem has already been solved in a different
way. This solution, which we shall now discuss, depends
on the employment of the musical electric arc.

The Musical Arc. — This phenomenon was first ob-
served by Lecher, and was more thoroughly investigated
later by Duddell and Peuckert* It consists essentially in
the production of a nearly sinusoidal alternating current
in a circuit containing inductance and capacity in parallel
with the arc (Fig. 107). In like manner oscillations are
produced in an organ pipe by the action of a steady
current of air connected to a vibrating system having a
definite period of vibration. The arc serves to convert the
continuous current into alternating current, and is, accord-

♦ It appears doubtful to the author whether Elihu Thomson, in
1892, observed this phenomenon or not (see pp. 179, 180; see also
American patent, No. 500,630, of i8th July 1892, granted 4th July
1893; The Electrician^ xlvi., p. 477, 1901 ; Iviii., p. 378, 1906; Iviii.,
p. 542, 1907 ; Electrical Review^ London, lix., p. 986, 1906 ; and
E.T.Z,y xxviii., pp. 304, 305, 1907).

Lecher, Wied. Ann,^ xxxiii., p. 693, 1888. See also Phys, Zeitschr.y
iii., p. 285, 1901.

W. Duddell, British patent, No. 21,629, o^ 29th November 1900;
The Electrician^ xlvi., pp. 269 and 310, 1900 ; and Proc, Inst. E.E.y
XXX., Part 148, 1901. See also Phys, Zeitschr,^ ii., pp. 425 and 440,
1901 ; also The Electrician^ 11., p. 902, 1903.

Peuckert, E.T.Z^y xxii., p. 467, 1901.

THE ARC AS HIGH FREQUENCY GENERATOR. I43

ing to Heinke's classification, a wave producer of the
second order, while the high frequency dynamo belongs
to the first order *

If the ohmic resistance of the shunt circuit is low its

N /

/ \

Fig. 107.
The Arc as Generator of Alternating Current.

frequency of oscillation is expressed, to a first approxima-
tion,f by the formula —

« =

2^n/LC

♦ C. Heinkc, Handbuch der Electrotechnik^ i., 2, p. 384, 1904.

t See also Tissot, E Assoc. Franc, pour T Avanc. des Sciences^ 1902,
and Eclair, Electr.^ xxx., p. 354, 1902 ; P. Janet, Comptes Rendus,
cxxxiv., pp. 462 and 821, 1902; J. K. A. Wertheim - Salomonson,
Tijdschrift v. Geneeskunde^ 1902, Deel i., p. 967 ; " Verslag der
vereenigung voor Electrotherapie en Radiologie^^ CompL Rend, du
deuxilme Congrh International de Radiologic et eTElectrologie Medi-
cales d. Bem^ 1902, p. 219 ; Stromsterkte en toonhoogte bij den fluiten-
den lichtboog., Proc, Amsterdam^ v., p. 311, 1902 ; Versl. Kon, Akad.
Amsterdam^ p. 381, 5th November 1902 ; Beibldtter^ xxvii., p. 792, 1903 ;
Courants de haute frequence non-amortis., Assoc. Franc. pourPAvance-
ment des Sciences^ Congres d'Angers, 4th to nth August 1903 ; Arch.
cPElecr. Med.^ September 1903 ; The^ Electrician^ li., p. 752, 1903, and
Eclair. Electr.^ xliii., p. 202, 1903 ; Ascoli andManzetti, Rendiconti dei
Uncei^ xi., (2), p. n, 1902 ; W. Mitkiewicz,/t?«r«. d. Russ. Phys. Chem.
Soc.^ xxxiv., p. 229, 1902, and Journ. de Phys.^ (4) ii., p. 223, 1903 ;
Corbino, Atti delta Annoc, Elettrot. Italianay vii., p. 597, 1903 ;

144

WIRELESS TELEPHONY.

The arc flickers in resonance with the shunt circuit, the
completion of the circuit producing at once a loud and pure
tone, whose pitch corresponds to the frequency of the

Current in
Arc.

Carrent in
Shunt.

Fig. io8.
Oscillograms of Arc arid Shunt Currents.

Arc Voltage.

Fig. 109.
Oscillogram of Arc Voltage and Shunt Current.

electrical oscillations. By varying the capacity and induc-
tions the pitch may be varied over a wide range.

Fabry, Eclair, Electr,^ x., p. 375, 1903 ; G. Grandquist, " Ueber die
Periode und die phasendifferenz zwischen Strom und Spannung im
singenden Flammenbogen," Boltzmann- Festschrift^ p. 799, 1904.

THE ARC AS HIGH FREQUENCY GENERATOR. I4S

Duddell-Arc Oscillograms. — Two oscillographic re-
cords from a singing arc, which Mr W. Duddell has very
kindly lent me, are reproduced in Figs. 108 and 109. Fig.
108 shows the variations of the current in the shunt circuit
and in the arc, and Fig. 109 the variations of the current in
the shunt circuit compared with the voltage on the arc*

In order to retain the oscillations in the shunt circuit
two choking coils are placed between its terminals and the
source of current. The arc should be about 2 to 3 mm.
long, between solid carbons,f the current being as small as
possible. These conditions may be expressed according to
Kaufmann's theory of discharge in gases by saying that the
arc must be on the falling branch of its characteristic, /.^.,
of the curve which expresses the relation between the voltage
at its terminals and the current in it, or symbolically —

dE . . *

-— ■ must be negative.!

Theory of the Vibrating Arc. — Of the numerous
theories § of the unstable arc which exist, that of Blondel
and Simon is the most complete. The "static" charac-
teristic of the carbon arc, determined by H. Ayrton, is
shown in Fig. no. It is a falling curve, and though it
explains the phenomena to a certain extent it does not
account for all the experimental results which have been

* In these photographs the curve for the shunt circuit appears to
be 180 degs. ahead of the second curve, since similar currents in the
two circuits produced opposite deflections on the oscillograph.

t If a sufficiently high voltage be used, a vacuum tube may be used
instead of a carbon arc.

{ W. Kaufmann, "Gottinger Nachrichten," p. 243, 1899, and^««. der
Physik,^ ii., p. 158, 1900; W. Duddell, he. cit; and H. Th. Simon and
M. Reich, Phys, Zeitschr,^ iii., p. 278, 1901, and iv., p. 364, 1903. Also
H. Th. Simon, Phys. Zeitschr,^ iv., p. 737, 1903, and vii., p. 435, 1906.

§ See, for instance, S. Maisel, Phys, Zeitschr.^ iv., p. 532, 1903,
v., p. 550, 1904, vi., p. 38, 1905 ; A. Blondel, Camptes Rendus^ cxl.,
p. 1680, 1905 ; H. Th. Simon, Phys, Zeiischr,^ vii., p. 433, 1906 ;
E.T,Z,y xxviii., pp. 295 and 314, 1907.

146

WIRELESS TELEPHONY.

obtained. Though one can see, for instance, why with a
small current, or a high voltage and large resistance in

series, it is much more
easy to start the oscilla-
tions than with greater
currents, the fact that
the frequency depends
both on the current and
on the length of the
arc remains unex-
plained, as also the fact,
which is of great im-
portance in wave-tele-
phony, that there is a
limit beyond which
the frequency does not
rise. The largest per-
missible supply current
to the arc is between
4 and 5 amperes, it

0»

t 3 f S

Fig. 1 10.
H. Ayrton's Characteristic Curve of the Arc.

being practically impossible to excite the oscillatory circuit
with a carbon arc if the current be greater. The theoretical
reason is the flatness of the curve, as shown in Fig. 1 10.*

* If in Fig. 1 10 a parallel to the axis of abscissae be drawn through
a point corresponding to the voltage £ of the supply, then the series
resistance will be represented by the tangent of the angle a formed by

THE ARC AS HIGH FREQUENCY GENERATOR. I47

The maximum frequency obtainable with the carbon arc
in air appears to be about 40,000 per second.*

A theory which agrees with all observations may be
based on the dynamical characteristic of the arc, which

so
10

•^ —

_-.

—^"^

S ♦ 3 * 1 I A 3 f

Ctmpite

Fig. in.

Hysteresis Curve of the Arc.

shows an arc - hysteresis, analogous to the magnetic
hysteresis of a circuit containing iron. This phenomenon
is essentially connected with the fact, noticed by Ayrton f

a line through £ to the point on the characteristic considered and by
the line drawn as above. The line from E to the characteristic is
sometimes called the resistance line. An increase in the series
resistance corresponds to a turning of this line so as to increase a ;
a rise of supply voltage to a parallel motion of the line in an upward
direction.

* Duddell explains this on the supposition that for high frequencies
(T^ldX becomes positive {The Electrician^ li., pp. 752, 1902, p. 126,
1903. See also Arch, f, d, ges. Physiol.^ cvi., p. 120, 1904). The
opinion of the author, who repeated these researches with exceedingly
small currents and obtained frequencies as high as 300,000, is that
we have here to deal with the impure Duddell phenomenon (see
Chapter XVII.).

t H. Ayrton, **The Electric Arc," London, 1902.

148

WIRELESS TELEPHONY.

and more exactly investigated by Simon* through the use
of an oscillograph, that the characteristic curve of an
alternating current arc shows lower voltages when the
current is decreasing than when it is increasing (see Fig.
III). It also depends on the supply current, the length
of the arc, the thermal conductivity and nature of the
electrodes, and on the nature, temperature, and pressure
of the surrounding gas. We thus find that, on taking
oscillographic records of the current and voltage of the
arc, we obtain a dynamical characteristic which shows

high voltages with increasing
currents, and low ones with de-
creasing currents, forming a
hysteresis loop (Fig. 112).

The complete process may
be described, in the case of the
Duddell phenomenon, as fol-
lows : —

The alternating current flow-
ing out of the oscillatory circuit
superposes itself on the constant
current in the arc, and thus
turns it into an oscillating cur-
rent, which lags 180 degs. behind
the current in the shunt circuit,
i.e.y it is increasing while the
shunt current is decreasing, and vice versa (see Fig.
113). Thus at the moment when the arc current passes
its maximum the shunt current goes through its mini-
mum ; the arc becomes smaller while the shunt current
increases and commences to charge the capacity. In
consequence of the slow cooling of the negative crater
the conductivity of the arc remains large, and hence the
voltage small. This is represented by the part ABC of the

1 %

Fig. 112.
Characteristic Curve of the
Oscillating Arc.

* H. Th. Simon, Phys. Zeihchr,^ vi., p. 297, 1905 ; E.T.Z.^ xxvi.^
pp. 818 and 839, 1905.

THE ARC AS HIGH FREQUENCV GENERATOR. I49

curve in Fig. 112. When the shunt current has reached its
maximum and begins to decrease, the current in the arc
again tends to increase, but on account of the lower con-
ductivity due to cooling of the negative electrode, a greater
voltage is required than before, and the part CDA of the
curve represents the conditions while the current in the arc

. F

Voltagi

on Arc, S 7°

in Vohs. I ^

Current
in Arc,
in Amps.

f 4-
3-

Current in

Oscillating )

Circuit,
in Amps.

\AAAA/

Fig. 113.
Oscillograms from the Oscillating Arc Circuits.

is increasing. The voltage increases until the cathode is
again white hot (d), and after this point the voltage rapidly
falls with increase of current (dea). Whenever the capacity
is charged it begins to discharge itself through the arc, thus
increasing the latter until the maximum current is reached
and the cycle recommences (a, Fig. 112). The fact that

ISO WIRELESS TELEPHONY.

the curve encloses an area indicates that energy has been
absorbed by the oscillating circuit.

Simon gives in addition a graphic method which lets
the conditions of the energy be more clearly seen, and
shows that in general more energy goes into the oscillating
circuit than comes out of it. This explanation, into which
we shall not go further, also shows why the amplitudes of
the voltage and current oscillations cannot rise above
certain values, and hence the oscillation attains a station-
ary state with great rapidity.

Such points as the inactivity of the arc with large
currents, the influence of the current and the length of
the arc on the frequency, and finally the impossibility of ex-
ceeding a certain limiting frequency, which is higher the
smaller the current, are all most clearly explained by
Simon's theory. The theory itself depends on the assump-
tion that the product of the temperature and area of the
negative crater is determinate for the drop in voltage
which produces a given current in the arc.

The immense importance of the singing arc for wireless
purposes was early recognised. Duddell and Simon indi-
cated that the production of this type of pure sinusoidal
electric waves would make tuning easy, and must solve the
problem of electric wave-telephony.* Although it was not
possible to make a practical application of the method so
long as a frequency of only 30,000 or 40,000 per second
was obtainable, this difficulty has also been overcome.

The investigations of Nussbaumerf and MoslerJ must
next be noticed, though they belong in reality to spark
telephony in that the singing arc is supplied by a trans-

* W. Duddell, British patent, No. 21,629, of 1900, "Complete Specifi-
cation," p. 4, lines 24-29; H. Th. Simon, E. T.Z.y xxii., p. 513, 1901 ; also
Simon and Reich, Phys. Zeitschr,^ iii., p. 278, 1901, iv., p. 364, 1903 ;
and Simon, Phys, Zettschr., iv., p. yyj, 1903.

t Nussbaumer, Phys. Zeiischr.^ v., p. 796, 1904, and E. T.Z.^ xxv., p.
1096, 1904.

X Mosler, E.T.Z.^ xxv., p. 1014, 1904, xxvi., p. 490, 1905.

THE ARC AS HIGH FREQUENCY GENERATOR. 151

former, and that the amplitude and frequency of the
oscillations are controlled by a microphone.

The same is true of Eisenstein's proposal to make an
inactive arc active when influenced by the sound waves.
For this purpose the primary coil of a microphone trans-

n\ <>

^-W\AA

-'/ ^

HoH|l|l I

E r

Fig. 114.

Koepsel's Method for the Transmission of Electric Waves which are

Identical in Form with the Sound Waves.

mitter, with so great an inductance that the arc no longer
sounded, was put in series with the oscillating circuit*

If now one speaks into a microphone connected to a
battery in series with the secondary coil, the inductance of

♦ S. Eisenstein, German patent, No. 166,678, of 8th July 1904 ;
British patent. No. 26,696, of 1904 (7th December 1904)-

152

WIRELESS TELEPHONY.

the primary is reduced, and the arc sounds in sympathy
with the voicfe. The oscillations thus produced are trans-
formed to a high voltage and supply an aerial wire in which
there is a spark gap.

The use of a spark gap in this system causes an
alteration in the frequency, and the production of trains of
damped waves following one another with great rapidity.
Koepsel* has, however, devised another method by which

Fig. 115.
Campos' Transmitter.

the comparatively slow oscillations of the musical arc may
be used directly for the excitation of the aerial wire without
the necessity of the latter being excessively long.f

* Koepsel, E, T,Z.^ xxv., p. 1 107, 1904. His patent here noticed (K.
24,734, Class 2ia, of 14th February 1903), which was published in the
Reichsanzdger of 13th May 1904, but was not completed owing to
non-payment of the patent fee, was kindly lent me on 4th February
1907 by Dr A. Koepsel.

t For a frequency of 40,000 per second the length of the aerial
would require to be A/4 = 1,875 metres.

THE ARC AS HIGH FREQUENCY GENERATOR. 153

This device consists in the shortening of the aerial
necessary for resonance by using a magnetic material or
by constructing it in a coiled or zigzag form *

The sound acts through a microphone, the current of
which is superposed on the supply current of the arc, and
thus directly or indirectly affects the aerial wire (see
Fig. 114).

Unfortunately, for want of financial support, Dr Koepsel's
laborious experiments came to no practical issue ; as he
himself expresses it, the modern commercial engineer is at
best a crassly egotistical Maecenas.

We must also notice here a transmitter designed by
Campos, in which the microphone is in parallel with an
inductance in the oscillating circuit, so that, on speaking
into it, the variations in its resistance cause temporary
corresponding alterations in the frequency of the oscil-
lations (Fig. 115).

The Beginnings of Wave-Telephony. — It was onl>'
after the singing arc had been utilised for the purpose of
producing electrical oscillatory currents that wave-telephony
became practical. Quite recently three methods have been
discovered by means of which the frequency of the arc
vibrations may be increased sufficiently for this purpose,
and these we shall consider before explaining their appli-
cation to wireless telephony.

* The frequency of oscillation of the aerial may also be reduced
by increase of capacity. For an arrangement of this sort see
Fessenden's American patent, No. 706,737, of 29th May 1901, and
German patent. No. 143,386, of 13th August 1902.

CHAPTER XIV.

THE POULSEN GENERATOR.

Poulsen. — Poulsen was the first to solve the problem of
the production of relatively intense oscillations of high
frequency by means of the Duddell phenomenon, by placing
the arc in an atmosphere consisting of a gas of high
thermal conductivity instead of in air.* Hydrogen, or a
compound of hydrogen, was found to be the best. He also
found that the apparatus works still better if the arc is
between a cooled metallic electrode as anode and a solid
carbon as cathode.f

* V. Poulsen, Danish patent, No. 5,590, of 15th December 1902,
granted 2nd April 1903 ; American patent, No. 789,449, of 19th June
I903> granted 9th May 1905; German patent, No. 162,945, of 12th
July 1903 (patent application, P. 15,041, Class 2i;f, published 20th
April 1905) ; British patent. No. 15,599, of 1903, application dated 14th
July. 1903, completed 13th April 1904, granted 14th July 1904 ; French
patent. No. 338,725, of ist December 1903, granted 6th June 1904,
and lecture at the Festsitzung der Electrotechnischen Vereins, 23rd
October 1906 {E, T.Z,^ xxvii., pp. 1029 and 1040, 1906), and lecture in the
Queen's Hall, London, 27th November 1906 {Engineering, Ixxxii.,
P- 734> 1907)- See Appendix for Fessenden's patents on same subject.

A mercury arc, or, with high voltages, a vacuum tube, may be
used (see Danish patent, No. 8,073, of 1904). It is interesting to note
that Righi had already used a vacuum tube in 1901-2 in researches of
the Duddell arc, and had found that one containing hydrogen gave
the best results (see A. Righi, "Sui fenomeni acustici dei conden-
satori," Memoria letta alia R, Accademia delle Scienze del VIsHiuto
di Bologna^ nella sessione del 25 Maggio 1902, Bologna, 1902, p. 8,
line 14).

t Simon mentioned in his lecture at the Scientific Congress in
Cassel that increased cooling of the arc or electrodes, and particularly
of the cathode, must have an important influence on the discharge,

THE POULSEN GENERATOR. 1 55

The electrodes used by Poulsen in his generator of
undamped electrical oscillations are shown in Fig. ii6.
The copper anode, which luckily does not wear at all
rapidly, was cooled by means of a current of water. The
cathode consisted of a carbon cylinder of comparatively
great diameter.

A transverse magnetic field is applied in order to keep
the arc in the best position, which is at the top with its
ends on the sharp edges of the electrodes.

In order to maintain the length of the arc constant,
which is of great importance, the carbon electrode is slowly
rotated on its axis, with a circumferential velocity of about

1 *^ >^^^^^M

Fig. 1 1 6.
Poulsen*s Arc Electrodes.

O.I mm. per second. After the carbon has made one
complete revolution it is necessary to put in a new one.
The arc is enclosed in a box with cooling arrangements,

but made no statement of results as he had then in hand a thorough
investigation of the whole problem (see I. Stark, Ann. d. Phys,, xii.,
p. 673, 1903, and Phys, Zeiischr., v., p. 264, 1904 ; also H. Ayrton,
"The Electric Arc," London, 1902 ; Gustave Grandquist, "Ueber die
Bedeutung des Warmeleitungsvermogens der Electroden beim elek-
trischen Lichtbogen," Kgl. Ges, d, Wiss. zu Upsala^ 1902, and Phys.
Zeitschr.y iv., p. 537, 1903 ; B. Monasch, " Der elektrische Lichtbogen,"
Berlin, 1904, p. 34 ; I. Stark and L. Cassuto, " Der Lichtbogen
zwischen gekiihlten Elektroden," Phys. Zeitschr.^ v., p. 264, 1904.

The alternating current in the oscillating circuit loses its sinu-
soidal form in Poulsen's arrangement in consequence of the difference
of the materials from which the electrodes are made.

Simon {E.T.Z.^ xxviii., p. 317, 1907) considers that the action of
Poulsen's arrangement depends entirely on want of symmetry of the
electrodes even in the case of two electrodes of the same material in
hydrogen (see also p. 181).

156

WIRELESS TELEPHONY.

through which the gas is passed. Poulsen has found that
ordinary lighting gas is very suitable. It should also be
stated that in this gas, as in others, the activity of the arc,
i,e.^ its power of producing high frequency oscillations,
depends on the current and on the length of the arc.

The arc only becomes active, with a water-cooled
electrode and difference of potential of 220 volts, when the
current is below 6 amperes ; the limit for an electrode which

Ml ' ' ^ M

* Fig. 117.

Poulsen's Arc with Magnetic Blast.

is not cooled being about 4 amperes. The frequency is
supposed to be about 500,000 per second in this case.
The arc must also be of a certain length, which Poulsen
calls the " active length," though after the oscillations have
commenced this may be somewhat reduced.* This active

* In his lecture in 1906 Poulsen showed clearly the influence of
the length of the arc but only mentioned the strength of current in

THE POULSEN GENERATOR.

157

length increases with the current and decreases with the
frequency. If the critical current is exceeded, or the active
length of arc not reached, the arc loses its property of
exciting oscillations and becomes inactive.

Both of these limiting conditions may be conveniently
controlled by the magnetic field used to fix the arc.
Although a permanent magnet* may be used if necessary
to fix the arc, Poulsen uses in his generator two large

B^HM^

Fig. 1 1 8.
Shunt Circuit Oscillator with Arcs in Series.

electro-magnets in series with the supply current to the
arc, which also serve as choking coils in the principal
circuit t (see Fig. 117).

connection with the amount of energy of the oscillations. "The
energy of the oscillations increases with the current in the arc, though
only up to a certain point." Further information is given in the
British and American patents — for instance, American patent, No.
789,449, p. I, line 90. "Experiments with this apparatus show that
as the intensity of the continuous current increases the amplitude of
the alternate currents diminishes or collapses and will finally cease,
but the reason is not at present known."

* Such a magnet is shown in the German patent (Fig. 11) and in
the provisional British patent (Fig. 16), while in the first American
and Danish patents there is no mention of a magnetic field at all.

t This arrangement occurs for the first time in the French patent
of 1st December 1903 (Figs. 4-6).

158 WIRELESS TELEPHONY.

This Strong magnetic field has the advantage that it
increases the voltage necessary to maintain any given
length of arc, a 3-mm. arc requiring, for instance, 440 volts,
and also that the arc remains active with considerably
larger currents.

This application of a strong magnetic field to the
widening of the active limits also produces, in the author's
opinion, an essential change in the character of the dis-
charge. The arc no longer sings freely, but executes
forced vibrations, a fact which is only indirectly noticed
by Poulsen, who remarks that the use of a strong electro-
magnet in series with the supply circuit generally enables
one to obtain a more powerful oscillation in the condenser
circuit* The influence of the magnetic field is clearly
shown in his wireless telegraphy experiments between
Lyngby and Esbjerg (about 300 km.), in which the energy,
originally amounting to only 100 watts with a supply
current giving 700 watts (240 volts and 3 amperes), rose to
400 watts with an energy supply of 2,800 watts (240 volts
and I i.y amperes).

Multiple Arcs. — In order to increase the radiation still
further, Poulsen uses several arcs in series in an atmo-
sphere of hydrogen.f It should be noted that for a given
supply voltage the radiated energy varies inversely as the
frequency, /.^., directly as the wave-length.

With this we come to the second method of producing
high frequency oscillations by means of the singing arc.

* See British patent, p. 6, line 51, ^?/ seg.^ "An essentially more
useful effect can be obtained by placing the conductor or the arc in
a magnetic field, the lines of force of which are perpendicular or
parallel to the conductor."

t The same end may be attained by increasing the pressure of
the hydrogen. (See also R. A, Fessenden, American patent, No.
706,741, of 5th November 1901, and S. Eisenstein, patent application
E. 10,087, Class 2ia, received ist June 1904 (refused).)

CHAPTER XV.

MULTIPLE ARCS IN AIR.

Experiment has shown that high fre-
quency oscillations may be produced by
the use of several arcs in series burning in
air (Fig. Ii8). An arrangement like this,
in which solid carbons are used, is shown
in Duddeirs patent,* and was given also
by Campos and Mosler, although it does
not appear to have been used for the
production of high frequency oscillations
until quite recently.f

Campos used, for instance, in one of
his carefully measured experiments, ten
arcs in series. The energy obtainable in
this manner is, however, comparatively
small, X though it may be somewhat in-
creased by the use of cooled metal elec-
trode as positive. This method has been
thoroughly developed by the Gesellschaft
fiir drahtlose Telegraphie in Berlin. Fig.

Fig. 119.

Vertical Water-
Cooled Arc.

♦ "Complete Specification," p. 3, lines 51, 52. See " Die Schwach-
stromtechnik in Einzeldarstellungen," vol. ii. ; D. Mazzotto, "Drahtlose
Telegraphie u. Telephony," p. 278, or English edition of same.

t H. Mosler, E,T,Z,, xxv., p. 1014, 1904.

X See W. Hahnemann, E.T.Z.^ xxvii., p. 1089, 1906, and xxviii., p.
353, 1907. The last reference is to a case in which the energy was
increased from 20 to 100 watts by using hydrogen.

i6o

WIRELESS TELEPHONY.

119 shows the construction.* The carbon electrode
reaches into the concave end of the copper vessel filled
with water, which forms the positive electrode. The regula-
tion of an arc of this type may be easily achieved if the
insulated carbons be attached to a piece of wood which
may be turned about a vertical axis. The copper elec-
trodes are placed above the carbons. The arcs are next

individually adjusted so
that by the motion of the
wooden support they may
be simultaneously struck
and regulated. Since the
wasting of the carbon
cathode is very slow when
used with this form of
anode, it is only necessary
to turn the support very
slightly from time to time
in order to maintain the
proper length of arc for
the production of oscil-
latory currents.

With a supply voltage
of 220 volts, six arcs may
be used in series, and so on
in the same proportion.

Fig. 120 shows a set
of six arcs constructed by
the author for experi-
mental purposes in which the arcs may be regulated either
separately or simultaneously.

As in the case of the Duddell phenomenon, there is a
critical value of the current beyond which no oscillations

Fig. 120.
Arcs in Series.

* The dissymmetry of the arc in the Poulsen generator holds also in
this case. (See also H. Th. Simon, E.T.Z.^ xxviii., p. 317, 1907). See
patent application G. 23,718, Class 21^, of 6th October 1906.

MULTIPLE ARCS IN AIR.

I6l

are excited.* The limit for a supply voltage of 220 volts,
and a frequency of 500,000, is about 5 amperes.

In the third method of this type metal electrodes are
used with a high voltage but small current arc.f We have
already noticed this system on p. 1 54.

The Author's Experiments on Limit of Frequency.

— The author has investigated and developed this method.

Fig. 120A. »

Adjustable Battery of Arcs.

The experiments were based on the fact that the critical
current of a singing arc is greater, the greater the capacity
of the condenser in the jig circuit. Oscillations would, for
instance, still be produced with a current of 20 amperes
at 220 volts if the capacity were about 1 50 microfarads.

* This phenomenon is the basis of an apparatus used by the
Gesellschaft fur drahtlose Telegraphie of Berlin, for testing arc oscil-
lators (Patent G. 23,994, Class 21a, of 3rd December 1906).

t See also B. Monasch, Patent M. 30,884, Class 21a, of 27th
October 1906.

1 62

WIRELESS TELEPHONY.

The author concluded from this consideration that, since
high frequencies necessitate small capacities, only small
currents can be used in their production. As, however, it

<
d

.SP

is under ordinary conditions impossible to maintain a small
current arc by connection to a central station supply, and
also because even if this could be satisfactorily done, the
energy would be too small for practical purposes, the

MULTIPLE ARCS IN AIR.

163

author decided to employ a high tension arc. The con-
tinuous current required for this purpose was generated by
several motor-driven dynamos in series ; each of these was
of 2 kilowatt output, and the total voltage attained was
2,500 volts. A photograph of the apparatus is shown in
Fig. 121.

A coil of high inductance and a variable glow-lamp
resistance of from 1,000 to 16,000 ohms were inserted in
the supply circuit to the arc.

Fig. 122.
Arc enclosed in Gas Chamber.

At first solid carbons were used, but these were shortly
replaced by aluminium rods or tubes. Later on a copper
rod was employed as anode, and a slowly rotating sharp-
cornered aluminium rod as cathode. The length of the
arc was usually only a fraction of a millimetre.

The energy may as usual be increased by cooling the
electrodes or applying a magnetic field. The disadvantage
common to the apparatuses used by Poulsen and by the
Telefunken Company, that the burning away of the elec-

i64

WIRELESS TELEPHONY.

Fig. I22A.

Fig. I22B.
Ruhmer's Moving- Wire-Electrode Arc Ap[)aratus.

MULTIPLE ARCS IN AIR. 165

trodes causes a variation in the frequency, may be over-
come by a simple method of construction, which, how-
ever, cannot be described until the completion of certain
patents.*

* Under certain conditions good results are also obtained by use
of a vacuum tube as discharger.

CHAPTER XVI.

APPLICATIONS OF THE ARC TO TELEPHONY,

Having described the three most important methods by
which high frequency currents may be produced,* we must
now turn to the application of these arc generators to the
purpose of transmitters in electric wireless telephony.

The following investigation shows clearly the method
of influencing the supply current to the arc.

The Author's H.F. Current Generator.— The author's
first successful experiments of this kind were carried out in
the summer of 1906, and were described in a communica-
tion, dated '23rd October 1906, to the members of the
International Conference on Wireless Telegraphy, at that
time sitting in Berlin, from which the following extracts
are taken : —

" A musical arc in an atmosphere of hydrogen, without
a magnetic blast, was used as generator, the supply current
being at 220 volts (see Fig. 122). The oscillating circuit
consisted of a condenser of about 0.02 microfarad made up
of seven Leyden jars, a variable inductance, and the primary
of a Tesla transformer. By careful adjustment of the
inductance (tuning) a quiet high tension arc of several
centimetres length could be maintained between the
secondary terminals of the transformer. On observation

* For similar methods see patents Class 21^, B. 43,661, of 17th July
1906, G. 23,377, of 21st July 1906, and G. 23,391, of 25th July 1906 ; also
S. G. Brown, "On a Method of producing Continuous High- Frequency
Electric Oscillations," The Electrician^ Iviii., p. 201, 1906.

APPLICATIONS OF THE ARC.

167

with a rotating mirror this arc appeared as a continuous
ribbon, like a constant current arc, for the oscillations,
which numbered about 300,000 per second, were far too
rapid to be distinguished individually. In like manner a
cathode ray oscillograph showed two graduated luminous
surfaces reaching to equal distances on opposite sides of
the zero line. It may be noted that the vacuum tube
oscillograph provides a convenient method of testing the
tuning of the circuits, and also shows very clearly, by the

M 10

Himiih

-VWWV

Fig. 123.
Ruhmer's Arc Generator.

amplitude of the motion of the cathode ray, the effects of
varying the distance between the electrodes or the strength
of current.

" An attempt was made to control this wave generator
in the way that a speaking arc may be controlled. For
this purpose a transformer was substituted for the choking
coil in the supply circuit, and had its secondary connected
to a microphone and battery (Fig. 123). The attempt was
completely successful, for on speaking into the microphone

i68

WIRELESS TELEPHONY.

the oscillographic tube showed in a rotating mirror a series
of bands corresponding to the sound waves, and no longer
a uniform ribbon."

Fig. 124, which is drawn from a very weak negative, is
a cathode ray picture of the vowel as seen in the rotating
mirror.

If the high tension arc described above be supplied with
this high frequency current it repeats every word spoken
into microphone even more clearly than an ordinary singing

Fig. 124.
Cathode Ray Oscillogram of Vowel O as Transmitted by Ruhmer's Apparatus.

arc would under similar conditions. From this experiment
there was only one step to the transmission of speech by
electrical waves.

The transmitting apparatus is shown in Fig. 125, and
the receiver in Fig. 126. A microphonic contact was at
first used as detector, but this was soon displaced by an
electrolytic cell which worked better.

These experiments, though only carried out in the
laboratory, gave astonishingly good results. With aerial
wires only 1.5 m. long speech was transmitted loudly and
clearly over a distance of 30 metres.

APPLICATIONS OF THE ARC.

169

There is no doubt that by the use of longer aerial wires
speech could be transmitted over several kilometres.

(§

mww-

vwwv

¥•

' J

^WWfJ

Fig. 125.
Ruhmer^s Transmitter.

Fig. 126.
Ruhmer's Receiver.

I hope to be able to report on such an experiment
immediately.

This experiment was carried out in December 1906,

I70 WIRELESS TELEPHONY.

between two dwelling houses in Berlin, at a distance of
about SCO metres from one another. The supply voltage
for the arcs was 440 volts, a high tension paraffin condenser
of about 0.031 microfarad was used in the jig circuit. The
length of aerial wire above the roof was in each case about
20 metres. The transmission of speech was perfect. Of
course the microphone current may be made to control the
field magnet windings of the supply dynamo, instead of
acting directly on the supply current, if desired, as we have
seen in the cases of the singing arc and the high frequency
alternator.

An attempt to control the arc by the use of a mano-
metric capsule on the^gas supply to the enclosed chamber
met with little success.

Better results were obtained by microphonic control of
a blast electro-magnet, which was either in the main supply
circuit, or in an independent one.

Instead of controlling the supply current directly, we
may, of course, use any of the methods previously described,
whether they consist in an alteration of the intensity or
frequency of the radiation. In this connection we may
notice particularly Campos' method of placing the micro-
phone parallel to the inductance of the oscillating circuit,
Fessenden's system of making it act directly on the aerial
wire, and finally the method of altering the strength of the
coupling between the closed and open oscillating circuits.
We may also cause the sound waves to render the arc
alternately active and inactive, a method which the author
has tried over short distances with success, and which has
enabled him to devise a simple and workmanlike method
which leaves little to be desired.

Further data on this subject must be looked for in the
technical journals of recent date.

The Nauen Experiments. — The Gesellschaft fur
drahtlose Telegraphie carried out in December 1906 some
similar experiments with a multiple arc transmitter.

Fir,. 127. —Complete Wireless Telephone Apparatus.

172 WIRELESS TELEPHONV.

Though details have not been published, it appears from
the notices in newspapers that the microphone current was
superposed on the oscillations in the aerial wire. An
electrolytic cell was used as receiver.

A description of the results of an experiment on 14th
December, between the Company's Berlin laboratory and
their station at Nauen, was given by Sydow at the meeting
of the Berlin Electrotechnical Society on i8th December
1906*

This experiment, however, does not, in the author's
opinion, give satisfactory information as to the capabilities
of the system, since, as was mentioned in Sydow's paper,
the stations were directly connected by a telephone wire,
along which the waves may have been propagated.

More certain results would be obtained from an experi-
ment in less favourable circumstances — for instance, across
the sea.

Fig. 127 shows the first complete sending and receiving
apparatus constructed by the above-mentioned Company .f

On the right stands the six-fold arc generator. The
regulating resistance is at the left end, and the choking
coils under the table. The microphone, fitted with a
funnel-shaped mouthpiece, is placed above.

The receiving apparatus is placed on the left side of
the table, and consists of the cell, the telephone, and a coil
which serves to tune the circuit to the aerial. Instruments
for measuring the currents complete the outfit. The switch
for changing over from sending to receiving is placed on
the middle of the table.

New Detectors. — To conclude this section we may
mention one or two detectors which have not yet been
applied to wireless telephony, but which appear to be very
suitable for the purpose. They are Hornemann's hot

* E.T.Z.^ xxvii., p. 1211, 1906.

t See Technische Rundschau^ xiii., p. 205, 1907.

APPLICATIONS OF THE ARC. 1 73

oxide coherer, and De Forest's audion and mercury vapour
detector, details of which may be found in the papers
referred to at the foot of the page.*

Coupling. — In all cases it is best to use as weak a
coupling as possible in the receiving apparatus between
the oscillating circuit and the aerial wire in order to obtain
a distinct transmission of speech. A strong coupling gives
a louder sound, but on account of the greater damping the
purity of the articulation is lost and the sounds become
unintelligible.

* Ann. d. Phys.^ xiv., p. 182, 1904 ; paper read before the American
Institute of Electrical Engineers on 20th October 1906, Proc, Amer.
Inst E,E.^ XXV., pp. 219-247, 1906; Electrical Worlds xlviii., p. 1107,
1906; The Electriciany Iviii., p. 216, 1906; see also J. A. Fleming,
Phil, Mag,^ May 1906; British patent. No. 24,850, of 1904, and Ameri-
can patent. No. 803,684, of 1905 ; and Tissot, yic?«r«. d. P>4yj., January
1907, and The Electrician^ Iviii., p. 729, 1907 ; Electrical Worlds
xlviii., p. 1 1 86, 1906; Eclair, Electr,^ 1., p. 144, 1907.

Further attempts : — H. Th. Simon, " Telegraphonic Receiver,"
German patent. No. 147,802, of ist March 1903, and R. A. Fessenden,
"Heterodyne Receiver," Zeitschr, f. Schwachstromiechn.y i., p. 116,
1 907. See Appendix.

OF THE ^

UNIVERSITY

OF ^

CHAPTER XVII.

THE DUDDELL PHENOMENON,

We have now described the two essentially different
methods of producing undamped electrical currents of high
frequency. In the one a high frequency alternator is used,
and in the other a singing arc. In the distortion of the
current curve due to the use of cooled metallic electrodes
in the Poulsen and Telefunken generators, both types pro-
duce a nearly sinusoidal current which is, of course, the
best for the purpose of resonance.

We shall now describe some similar phenomena in
which high frequency alternating currents are used, though
they are no longer even approximately sinusoidal. These
may, however, be used for wireless telegraphy and tele-
phony, and give a considerably larger amount of energy
in the oscillating circuit*

The Phenomena Intermediate between the Stable
Arc and the Spark. — Let us commence with the singing
arc in our attempt to deduce a definite and comprehensive
explanation of the mass of contradictory views, observa-
tions, and explanations which have been published on the
subject of arc generators.

If, in an arrangement of this type, the supply current is
gradually decreased by increase of the series resistance,
there comes a time when the amplitude of the oscillation
in the condenser circuit becomes so great that during the

♦ Hahnemann's view {E. T.Z.^ xxviii., p. 353, 1907), that the
methods about to be described are not suitable for wireless telephony,
appears to the author to be incorrect.

THE DUDDELL PHENOMENON.

175

half period while charging is taking place in the shunt
circuit, the current in the arc falls to zero.

This case is shown in Figs. 128 and 129, which are
from oscillograms which Mr Duddell has kindly lent me
(see footnote, p. 145). We see from these that even near

Current in Arc.

Currcnl in Shunt Circuit.

Fig. 128.

Voltage on Arc.

Current in Shunt Circuit.

Fig. 129.
The Limits of the Duddell Phenomenon.

the limit of the Duddell phenomenon the current in the
oscillating circuit is still approximately sinusoidal.

When the supply current is still further decreased the
amplitude of the oscillation increases, and the current in
the arc no longer merely touches the zero line but actually

176

WIRELESS TELEPHONY.

remains at this value for some time, so that on the return
swing of the current the arc is struck afresh, and the slower
the electricity flows from the source of supply the longer
does the capacity take to reach the voltage necessary
before this occurs.*

As we have seen in the theoretical discussion on p. 125,
the time the arc takes to strike depends on the resistance

Arc Voltage. < 20

(■

Arc Current
(\mps).

Shunt
Current
(Amps).

UHiia

Fig. 130.
Arc giving Forced Vibrations.

and inductance of the supply circuit. The period of the
oscillating circuit in this case depends not only on the

♦ The same happens if too much energy is forced into the oscillat-
ing circuit of Duddell*s arrangement (see also * W. Hahnemann,
E. T.Z,^ xxvii., p. 1090, 1906). The gap between the electrodes must
in this case be only a fraction of a millimetre.

THE DUDDELL PHENOMENON. 1 77

constants of the circuit but also on the magnitude of the
supply current, and the phenomenon may therefore be
called an imperfect or impure Duddell effect.

The current and voltage curves for this case are shown
in Fig. 130. It will be seen that the current in the oscillat-
ing circuit no longer forms a sine curve.

A singing arc which should have, from its electrical
dimensions, a frequency that would give a musical note, gives
under these conditions merely a hissing or screeching noise.

One may also deduce this result graphically from Fig.
no by displacing the point defining the conditions of
supply in the direction of less current. As soon as the
" resistance line " drawn through the point E becomes a
tangent to the characteristic, or more exactly to the
diminishing current side of the hysteresis curve at the
point considered, the limit of stability of the arc is reached
and the arc goes out and remains extinguished until the
voltage has risen so much that it strikes afresh.*

We might be inclined to conclude from this explana-
tion that the determining factors are the same in both the
pure and impure Duddell phenomena ; this is, however, not
the case.

The phenomenon we are now considering is in fact a
much more general one, being in reality a form of the
ordinary spark discharge in which a series of damped wave
trains follow one another with great rapidity, but in which
the sparking rate is in no way directly related to the
frequency of the oscillations produced at each spark. In
this impure Duddell phenomenon the second period of the
oscillatory discharge does not coincide with the second
period of the current in the arc, and therefore there is no
continuity in the succession of waves produced.

From this more general standpoint we see that the
impure Duddell phenomenon consists in a succession of
partial discharges following one another in trains.

* A. Blondel, Comptes Rendus^ cxl., p. 1680, 1905.
M

1/8 WIRELESS TELEPHONY.

The conditions for the existence of this process are
quite different from those for the singing arc. In particular
we note that energy passes in this case into the condenser
of the oscillating circuit while the arc is extinguished, a
circumstance not taken account of in Duddell's condition
that dE/dl should be negative. As a matter of fact this
condition does not come into consideration at all in pheno-
mena of this kind, as Maisel has shown by both theoretical
and experimental researches.*

The nature of the electrodes plays an essentially differ-
ent part from that which it does in the singing arc, and
has no effect on the frequency of the oscillations excited by
the intermittent arc.

The above is the author's explanation of the observa-
tions, mentioned on p. 146 as being contradictory to the
theory of the singing arc, on the appearance in the oscil-
lating circuit of oscillations which are not sinusoidal.f and
finally the establishment of the unsuitability of the Thomson
formula for calculating the frequency, simply because this
formula is in reality applicable to the impure Duddell
phenomenon, which, in spite of its resemblance to the
singing arc, is essentially different in principle. J

The possibility of substituting a mercury lamp, in which
the quantity cfE/dl = O, as Weintraub has shown, with slow
alterations of current, for the arc, is also intelligible. §

With the continuous current voltages usually available
(from no to 550 volts) special means must be employed to
render the cathode again active, since mercury vapour
rapidly loses its conductivity.il

* S. Maisel, /oc\ ciL

t Corbino, loc, cit

X Ascoli and Manzetti, loc, cit,^ and A. Masini, Elettricista^ xi.,
P' 233, 1902 ; also Eclair. Electr.^ xxxiii., p. 310, 1902.

§ See, for instance, Valbreuze, Eclair, Electr,^ xxxvi., p. 81, 1903 ;
E,T,Z,, xxiv., p. 831, 1903.

II Warming the cathode or adding a secondary arc are instances
of ways of accomplishing this (Weintraub). See German patent,

THE DUDDELL PHENOMENON.

179

The true rdle of the arc in this type of apparatus is still
more evident when a high tension direct current is used.
Simon's researches, mentioned on pp. 125-128, were made
with the purpose of producing a continuous undamped
oscillation from a series of separate impulses.*

Simon did not succeed, as we have seen, but only
obtained a rapid succession of trains of damped waves.

If the realisation of the necessary conditions offers great
difficulties in a mercury vapour arc, it is clear that with an
ordinary air gap the difficulty
is even greater, since all the
hindrances occur in a higher
degree.

Elihu Thomson's Ameri-
can patent, No. 500,630
(1892), which has been so
frequently, and, in the author's
opinion, erroneously, quoted
as the precursor of the singing
arc, belongs to this group.f
Fig. 131 is taken from the
patent specification.

It is clearly obvious from
both the text and scope of the
patent claims that in Thom-
son's arrangement a spark
gap, and not a continuously burning arc, is used. The

Fig. 131.

E. Thomson's High Frequency

Generator.

No. 173,396, of 27th September 1904, in which a similar arrangement
of the author's is shown.

* See Cooper Hewitt's American patents, Nos. 780,999 and 781,000,
both of 25th April 1902, and No. 781,603, of 24th September 1902, all
three granted on 31st January 1905 ; Electrical Review^ xlii., p. 264,
1903 ; Electrical World, xli., p. 326, 1903. Cooper Hewitt gives
3,500 volts as a suitable voltage.

H. Th. Simon and M. Reich, Phys. Zeitschr., iv., p. 364, 1903, and
H. Th. Simon, Phys. Zeitschr,, iv., p. 737, 1903.

t Application dated i8th July 1892, granted 4th July 1893. See
also Elihu Thomson, The Electrician, xlvi., p. 477, 1901, Iviii., p. 542,

I80 WIRELESS TELEPHONY.

electro-magnet, shown in Fig. 131, which, according to
Thomson, is otherwise quite unnecessary* for satisfactory
working, serves exactly the purpose of preventing the series
of discharges becoming an arc.

Hence there can hardly be a doubt that fundamental
idea of the patent deals with a disruptive discharge.
Whether Thomson in these experiments really obtained
a succession of single impulses, or, which appears much
more likely, a series of damped wave trains, must be left
undecided. It is also not impossible that Thomson may
have actually observed the pure Duddell phenomenon, in
which case, however, he did not recognise the differences
in action under different conditions, and only described one
of the possible processes, which happened to be one the
principle of which is different from that of the singing arc.

The difficulties which we have noticed that arise in
attempting to maintain the necessary conditions for a dis-
ruptive discharge may be partially overcome by special
artifices as Simon has shown. f

1907 ; Electrical Rtn'te^v (London), lix., p. 986, 1906; E.T.Z.^ xxviii.,
pp. 304, 305, 1907 ; R. A. Fessenden, The Llectrician^ Iviii., pp. 675
and 710, 1907. Fessenden, in his American patent, No. 730,753
(application 9th April 1903, granted 9th July 1903), expresses an
exactly similar view of the Thomson arrangement as that given above
by the author (see p. 2, lines 86-88) — " In the Thomson patent the
oscillation frequency is identical with the discharge frequency." His
standpoint is all the less comprehensible as he proceeds to identify
the Thomson with the Duddell phenomenon. Further, "The Arc in
Wireless Telegraphy," The Electrician^ Iviii., p. 374, 1906 ; and J. A.
Fleming, The Electrician^ Iviii., p. 733, 1907 ; also L. H. Walter,
" The Arc and Spark in Wireless Telegraphy," Electrical Engineeringy
7th February 1907.

* See American patent, No. 500,630, p. i, lines 73, 74 — "At M is
represented a powerful magnet which is not always, however, neces-
sary, but the purpose of which is to break any arc between the balls
at G. It may sometimes be replaced by an air jet;" and The
Electrician^ li., p. 542, 1907 — "Neither was the dying spark suddenly
blown out by a magnet or air blast, because in the course of my ex-
periments I found that neither of these adjuncts was necessary."

t H. Th. Simon, Phys, Zeitschr.^ iv., pp. 372 and 740, 1903.

THE DUDDELL PHENOMENON. l8l

One of these methods consists in causing so great a
transference of energy from the oscillating circuit to the
aerial wire at each discharge that the jig is very suddenly
damped out, and the air gap returns very rapidly to its
non-conducting state.

Unsymmetrical Electrodes. — A still more simple and
certain method of attaining the same end is to use unsym-
metrical spark gaps which act as valves, since they require
a greater voltage in the one direction than in the other,*
if one arranges the voltage so that the discharge of the
capacity occurs at the lower voltage, and hence the voltage
of the next half wave is not sufficient to cause a new spark.
The use of these unsymmetrical spark gaps has been very
frequently suggested,! and has been carried out by Simon.

Righi, for instance, used, in his experiments in 1901, a
Geissler tube which had a flat cathode and a pointed anode
as spark gap (see p. 154). The current curves which he
obtained by means of a Braun's oscillograph show clearly
that he actually obtained a series of single impulses, which
followed each other in the way to be expected from theory
on consideration of the constants of the supply circuit, and
of the oscillating circuit.

It appears not impossible that a dissymmetry of this
kind may also arise through the heating of one electrode,
and the cooling of the other. Simon's explanation of the
action of Poulsen's generator depends on this hypothesis, J
which, however, is not in agreement with the author's results
described below.

* A valve may also be put in series with the spark gap (see for
instance A. Blondel, British patent. No. 15,527, of 1902, p. 5, lines 17,
18 ; also H. Th. Simon, E,T.Z.^ xxviii., p. 317, 1907).

t R. A. Fessenden, American patent, No. 706,741, application 5th
November 1901, granted 12th August 1902 ; A. Blondel, British patent.
No. 15,527, of 1902, applied for nth July 1902, completed nth April
1903, granted nth July 1903, p. 5, lines 17 and 38, 39 ; H. Th. Simon,
ioc. cit.^ and German patent, No. 156,364, of 26th March 1903.

X H. Th. Simon, E,T,Z.^ xxviii., p. 317, 1907.

1 82 WIRELESS TELEPHONY.

A very large number of proposals for the control by
sound waves of a disruptive discharge transmitter are de-
scribed in Blondel's British patent, No. 15,527, of 1902.*

We must also notice here the difference between the
process employed in this system of wireless telephony and
the Duddell phenomenon, thus (p. 5, lines 27-30), "It may
be noticed that the appearance of Fig. 2 is analogous to
that of the well-known arrangement and patent of Duddell,
No. 21,629, of 1900, on the musical arc : but an essential
difference is the employment of a disruptive discharger instead
of an arc!*

In the methods so far described for the production of
undamped electrical oscillation by means of an arc or
spark we have dealt with a phenomenon which only occurs
under certain definite conditions in regard to the constants
of the coupled circuits. • In a certain sense the capacity
plays the most important part in the action. Since the
choking coil in the supply leads allows only slow variations
in the supply current to take place, the charging of ihe
Condenser takes energy from the arc or spark gap, so that
the current is considerably diminished (Duddell pheno-
menon), falling under certain circumstances- momentarily to
zero (limit of the Duddell phenomenon), or remaining at
zero until the voltage across the gap has again risen suffi-
ciently to cause a discharge (impure Duddell phenomenon,
disruptive discharge process).

* See also A. Blondel, German patent, No. 160,880, of 17th August
1902.

CHAPTER XVIII.

FORCED VIBRATIONS,

In conclusion we shall describe still another group of
methods in which, unlike those previously mentioned, the
arc itself must be considered as the actual generator, and
in which the oscillations in the shunt circuit are merely
forced.

Forced Vibrations. — This process will be most easily
understood if an apparatus is considered in which the
discharge gap is supplied with alternating and not direct
current. Clearly in this case we shall have the greatest
oscillations in the shunt circuit when its natural period is
the same as that of the supply current, i.e.y when there is
revibration (resonance) between the impressed and free vibra-
tions. An arrangement of this kind would have no practical
value if it were necessary to produce the high frequency
supply current mechanically — by means of an alternator, for
instance — since the secondary circuit would then be un-
necessary. These variations or interruptions of the direct
current supply may, however, be caused in a very simple
manner by the application of a magnetic or air blast to the
spark gap.

De la Rive has observed* that an otherwise quietly
burning direct current arc, when placed in a magnetic field
gives out a loud noise, " like the hissing of the steam blown
off from a locomotive."

* De la Rive, Pogg. Ann., Ixxvi., p. 281, 1849.

1 84

WIRELESS TELEPHONY.

This observation indicates that relatively rapid oscilla-
tions are taking place in the arc, and, in fact, these may
become so great that the arc is extinguished.

This rapid succession of extinctions and strikings of the
arc in a magnetic field has been since observed by other
experimenters. Blondel (1893), for instance, gives 3,000 to
4,000, and Abraham (1899) as much as 100,000 per second.

Fitzgerald suggested that by such a rapid succession of
interruptions of an arc it might be possible to produce high

Vie. 132.
Ruhnier's Arc Interrupter.

frequency currents. This is particularly interesting, since
it was from this point of view that Duddell was investi-
gating the influence of a magnetic field on the arc before
his discovery of the musical arc. Since, however, the in-
terruptions were too irregular no result was obtained.

The author has found that the regularity of the inter-
ruptions may be much increased if a parallel circuit, whose
natural period is the same as that of the action in the supply
circuit, is connected to an arc controlled by a magnetic or

FORCED VIBRATIONS. 1 85

air blast.* Still more satisfactory results were obtained
when the action of the blast was in time with the oscilla-
tions, a condition most easily attained by putting the
magnet in series with the arc. We have thus to do with an
arrangement which is, to say the least, very like that used
by Poulsen in his arc generator (see Fig. 117).

The Arc Interrupter. — The author's arc interrupter,
invented in 1903, depends on this principle (see Figs. 132
and 133); it was shown in the Exhibition of Electrical
Novelties in Berlin f (22nd to 27th November 1904), and
described in the Elect lotechnische Zeitschrifl^ xxvi., pp. 382,

383.

The author clearly indicated the importance of this
apparatus as a generator of high frequency currents at a
demonstration before the Leipsic Electrotechnical Society,
on I2th January 1905. J

Since the supply voltage controls the speed of increase
of the current, and the strength of the magnetic blast the

* H. Mosler later described a similar arrangement, and noticed
that resonance must occur between the electro-mechanically excited
oscillations of the arc and the current in the parallel circuit (E.T.Z.^
xxviii., pp. 142 and 304, 1907).

+ At this Exhibition this apparatus was shown both as interrupter
for a 30 cm. induction coil (the primary winding of which in series
with a comilenser formed the oscillating circuit), and also as a generator
of high frequency alternating currents.

X See E. T,Z,^ xxvi., p. 383, section i below : " To show that this
interrupter serves also for the production of high frequency currents
an impedance coil was supplied from it. The rate of interruption was
in this case about 20,000 per second, but could, however, be increased
by alteration of the natural period of the oscillating circuit to 400,000
per second, as was shown by a cinematographic record. By this
means the hitherto insoluble problem of the production of continuous
oscillations of hij^h frequency has been solved in a very simple manner. ^^
See 3\so Mechaniker^ xiii., p. 13, 1905 ; A. Prasch, "Die Fortschritte
auf dem Gebiete der drahtlosen Telegraphie," iv., pp. 178 and 266,
1906; further, A. Righi and B. Dessau, "Die Telegraphie ohne Draht,"
2 auflage, pp. 405, 406, 1907.

1 86

WIRELESS TELEPHONY.

FORCED VIBRATIONS.

187

rapidity of its fall, both factors must be taken into account
in order that the parallel circuit may be subjected to the
impulses at the right moments.

By means of a high tension arc in air fitted with the
above-described apparatus, high frequency alternating
currents suitable for use in wireless telegraphy and tele-
phony have actually been produced.

In contrast to the Thomson arrangement, in which, under
proper conditions, free oscillations take place in the shunt
circuit, this arc interrupter causes only a forced' oscillation
by the action of the
varying magnetic
blast. While in the
one case the inde-
pendently excited
magnetic blast serves
mainly to prevent the
formation of an arc,
and may be left out
under certain circum-
stances without harm,
in the arc interrupter
it plays the principal
part, and without it there would be no excitation of the
oscillatory circuit.

Finally, we must mention, though it seems almost super-
fluous to do so after what has been said, that of course the
arc interrupter does not conform with the conditions for
the singing arc. Experiments show, for instance, that
rapid oscillations may be produced when soft-cored carbons
are used, for which, as Frith and Rodgers* have shown,
dKjdl is positive.

If the Duddell phenomenon is analogous to the ordinary
organ pipe, the arc interrupter corresponds to the reed pipe,
in which the column of air is forced to vibrate synchro-

FiG. 134.

Oscillograms of Forced Vibrations.

* Frith and Rodgers, Phil. Afajs^.y vol. xlii., p. 407, 1896.

i88

WIRELESS TELEPHONY.

nously with the tongue. And just as in the reed pipe the
vibrations of the air column react on the reed, so do

Current.

Fig. 135.

Characteristic of Short Arc with Eorced Vibrations : Complete Extinctions

of Short Duration.

Current.

Fig. 136.

Same as 135, but Longer Arc ; Voltage also falls to zero in this case. Times

of Extinction Longer.

the currents in the oscillatory circuit react on the arc
interrupter.

The method we have just described has the great

FORCED VIBRATIONS.

189

advantage over previous ones that it is possible by its
means to cause oscillations of almost any desired energy.*

In the explanation given above of the arc interrupter,
we have assumed that the blast magnet causes a complete
extinction of the arc. The current must therefore not only
fall to zero, but must remain at that value for some time
before it rises again. That this is actually the case is
shown in the typical arc interrupter current curve of Fig.
134, taken oscillogra-
phically with about
four hundred inter-
ruptions per second.

Even if the action
of the magnet is so
weak that it does not c
cause a complete ex- J
tinction of the arc, it is ^
probable that a perio-
dic oscillation of the
latter is produced,
since the connection
of the windings of
the electro-magnet in
series with the arc
must produce a
mutual interaction. t

By making the process relatively slow it is possible to
prove the existence of an oscillation of this kind above the
zero line by means of a Braun's tube. Unfortunately it is
very difficult, indeed almost impossible, to observe high fre-
quency current curves with an ordinary oscillograph with an
accuracy sufficient to enable a distinction to be made between
a complete interruption and a partial oscillation of the arc.

Current.

KiG. 137.
More Unfavoural)le Conditions.

♦ See also W. Hahnemann, E,T.Z.^ xxviii., p. 353, 1907.
t M. Reithoffer denies the possibility of the production of un-
damped wayps by such an action, E.T.Z.^ xxviii., p. 308, 1907.

190 WIRELESS TELEPHONY.

Characteristic Curves of Various Types of Dis-
charge. — If, however, we adopt Simon's arrangement,
we can obtain a photographic record of the dynamic
characteristic. In this method the cathode ray is acted on
by magnetic fields at right angles to one another, one of
which is due to the current, and the other to the voltage,
in the oscillating circuit. The cathode ray strikes a fluor-
escent screen, producing a spot of light which describes
the characteristic curve since each point is defined by the
current and voltage at the moment. The motion of the spot
is so rapid that the curve appears steadily on the screen,
and may be photographed.

F^&s. 13s to 137 show some characteristics of an arc
interrupter taken by the author. The axes of co-ordinates
may be determined by the position of the points seen in
the figure. This method is applicable to currents of any
frequency.

The zero point of the current flowing in the voltage
coil is displaced to the left since the deflection is caused
electro-magnetically ; it may also be produced electro-stati-
cally as Wehnelt has shown.

Figs. 135 and 136 correspond to cases in which the
current falls to zero, and there is a complete interruption
and extinction of the arc. Fig. 135 was taken with a short,
and Fig. 136 with a long arc; the conditions being
otherwise similar. In the latter, as the characteristic
clearly shows, the voltage also fell momentarily to zero.

Fig. 137 is a complicated curve taken under unfavour-
able conditions of the arc interrupter. Without going
further into it at present we may notice that there was a
complete extinction of the arc in this case.

In addition to these curves similar ones were taken
with comparatively short arcs. One of these has been
transferred to the diagram. Fig. 138, in which it is marked
I ; it does not touch the axes at any point, and the lowest
value of the current is at most i ampere. Curves 2 and 3
correspond to the characteristics in Figs. 135 and 136.

FORCED VIBRATIONS.

191

For purposes of comparison the characteristics of
the singing arc (marked D) and of the Poulsen generator
(marked P) are included. It should be noticed that the
steepness of the Poulsen curve, as compared with those
taken from arcs in air, is due to the atmosphere of hydrogen
in which the arc burns.

It may be remarked that under the conditions adopted
by the author for the observation of the Poulsen generator.

Volts

300

200

100

2 4 6 8 10 12 U 16 18 20 Amperes

Fig. 138.
Characteristic Curves of the Duddell, Poulsen, and Arc Interrupter Currents.

a characteristic corresponding to a complete extinction of
the arc, />., one which touched the axes of co-ordinates,
was only obtainable just before the arc went out altogether,
and could not be maintained for any length of time.*

These observations in no way exclude the probability

* This observation does not agree with Simon's earlier theory of
the Poulsen generator (see p. 155).

192 WIRELESS TELEPHONY.

that the Poulsen generator acts by producing a forced
vibration in the shunt circuit. A similar explanation has
been given by Benischke of the action of a very similar
arrangement.*

The author has given his opinions on the subject in
letters to the technical papers from which the following
paragraphs are taken : f —

" Poulsen apparently only used the magnet, at first, to
fix the position of the ends of the arc.

" It was only later, as I gather from the progress of the
discovery, that he strengthened the magnetic field in order
to maintain the arc active in spite of a greater supply of
energy, since the Duddcll phenomenon no longer occurs with
large currents, even with cooled electrodes and a hydrogen
atmosphere. The arc then becomes stable and hence
inactive. A powerful magnetic, or air, blast which breaks
the arc, is then necessary in order to excite the oscillating
circuit.

*' Poulsen thus, whether knowingly or unknowingly is
of no consequence, superposed his hydrogen atmosphere on
my arc interrupter.

" I agree with Herr Benischke that after Herr Poulsen's
demonstration to the Electrotechnical Society, we must
come to the conclusion that the apparatus shown was
only my arc interrupter working in an atmosphere of
hydrogen."

This explanation is, however, based on the erroneous
assumption that the Poulsen generator acts through inter-
ruptions. As we have seen above, and as Benischke has
also noticed, * it is of no consequence whether the inter-
ruption is complete or not, or whether the current reaches
a zero value, for the real characteristic of the method is the

* G. Benischke, E.T.Z.^ xxvii., p. 121 2, 1906-
t E. Ruhmer, E.T.Z.^ xxviii., p. 69, 1907.
X G. Benischke, E.T.Z.y xxviii., 1907.

FORCED VIBRATIONS. I93

production of forced oscillations in the shunt circuit through
the action of the external agencies.*

The Mercury Arc. — Finally, we must mention that in
an arrangement of this kind a mercury arc may be used
instead of an ordinary arc.

As long as the blast electro-magnet is required only for
the purpose of causing oscillations and not as an inter-
rupter, ordinary supply voltages may be employed. With
stronger action, when the arc is actually extinguished, it is
necessary to use some method of increasing the activity
of the cathode, and for this purpose a high tension con-
tinuous current is most suitable.

In conclusion, we shall describe shortly an apparatus
of Vreeland's for the production of undamped oscillations.f
In this a mercury lamp is used which has a mercury
cathode and two anodes. The connections shown in Fig.
139 are only diagrammatic, as the electro-magnets are in
reality placed vertically to the plane through the anodes.
When the apparatus is in working order the current flows
practically equally to both anodes ; the slight differences
between them cause, however, oscillations and hence varia-
tions in the field of the electro-magnets. This results in
the current ray being pulled over towards one or other of
the anodes, and at once the field of the magnet connected
to this side is strengthened, and the current is driven back
to the other anode which strengthens the field of the other

* G. Benischke, E.T.Z,^ xxviii., p. 354, 1907. Benischke here
makes the remark that a similar phenomenon must arise through the
magnetic coupling of the secondary oscillating circuit to the arc
circuit if the arc is used as an oscillation generator. As a matter of
fact oscillations may be produced by an arrangement of this kind, as
the author's experiments have shown ; while in Duddell's apparatus,
where the condenser is the oscillation producer, the substitution of a
magnetic coupling for the electric one is not possible.

t K. Vreeland, The Electrician^ Iviii., p. 685, 1907 ; and E,T,Z,y
xxviii., p. 276, 1907.

194

WIRELESS TELEPHONY.

magnet. The result is an oscillatory current of high
frequency in the main circuit

A transmitter for wireless telephony is shown connected
to this generator in Fig. 139.

The voice controls the electric radiation by means of a

microphone whose current
alters the coupling between
the primary and secondary
systems.

Fig. 139.

Vreeland*s Twin Electrode Mercury
Vapour Discharger.

The Function of Open-
Circuit Wireless Telephony.

— Electric wave - telephony
forms a most valuable exten-
sion of wireless telegraphy,
since stations fitted for the
latter may easily be adapted
to the former, but it is not
likely that it will to any extent take the place of wire-tele-
phony, at least for some time to come, since a rapid change-
over from speaking to hearing is not possible. A listener at
a wireless telephone must wait patiently until the speaker
has finished, and then must change over his switch before
he is able to answer.*

With the oscillations of small intensity which it is
possible to produce by means of the human voice, it
appears unlikely that great distances will be bridged. On
this account the field of electric wireless telephony seems
at present to correspond with that of light-telephony.

Without doubt the new method of communication
will prove useful by its great suitability for such purposes
as communication between ships and for military work.

♦ At the same time it is possible that wireless telephony will have
a considerable influence on the development of wire-telephony. We
may notice, for instance, the problem of multiplex telephony, the solu-
tion of which may lie in the adoption of wireless methods.

FORCED VIBRATIONS. 1 95

Electric wave-telephony possesses all the advantages
and disadvantages common to every method of communi-
cation by electric waves. One of its advantages is that
the stations need not be in sight of one another, while its
main disadvantage is the difficulty of maintaining absolute
secrecy and freedom from interruption.

If one compares wave-telephony with light-telephony
it is seen that the advantages of the one are the disadvan-
tages of the other, and vice versa. Thus in a case where it
is desired to send the voice in a certain direction only, a
beam of light is preferable ; while, on the other hand,
the condition of the atmosphere, so important in light-
telephony, is of practically no consequence in wave-
telephony.

CHAPTER XIX.

CONCLUSION,

We have seen in the foregoing how the problem of the
wireless transmission of human speech has been solved.
There are two principal and very similar methods : — light-
telephony and wave-telephony, the former almost as old
as the telephone itself, and the latter a child of most recent
growth.

Great advances may be expected in the latter since it
is still in a very early stage of its development, and there
can be no doubt that, as on every side energetic attempts
are being made to improve it, its progress from day to
day must be very rapid.

Although the principle of the method has been obvious
for a long time, it is only quite recently that theory has
been converted into practice.

While it is only a few months ago that the great in-
ventor Edison rightly gave to the question, " What is the
outlook for wireless telephony?" the answer, " It does not
exist," we are already in the position to transmit speech
wirelessly over several kilometres. Indeed Fessenden and
Tesla have already, in somewhat fanciful manner, prophe-
sied that radiotelephony will be the telephony of the
future.

** With proper apparatus telephonic communication will
be carried on with ease and precision to the greatest
terrestrial distances, and very soon it will be possible to
speak across an ocean as clearly as across a table." So
prophesies Tesla in the English Mechanic, Ayrton's picture

CONCLUSION. • 197

of the future would then have nearly attained its ful-
filment: —

" The day will come, when we are all forgotten, when
copper wires, guttapercha covers and iron bands are only to
be found in museums, that a person who wishes to speak
to a friend but does not know where he is, will call with an
electrical voice which will be heard only by him who has a
similarly tuned electric ear. He will cry, * Where are
you ? ' and the answer will sound in his ear, * I am in the
depth of a mine, on the summit of the Andes, or on the
broad ocean.' Or perhaps no voice will reply, and he will
know that his friend is dead."

Returning to accomplished facts, we must admit that,
if even in only a limited degree, wireless telephony will be
of service to mankind.

APPENDIX.

RECENT ADVANCES IN THEORY AND
PRACTICE,

By James Erskine-Murray, D.Sc.

Latest News. — Since the publication of Mr Ruhmer*s
book in the spring of this year (1907), a good deal of
matter of both theoretical and practical interest in wireless
telephony has been published. Of the latter, perhaps the
most interesting item of news is the recognition of the
practical value of wireless telephony as a means of com-
munication in warfare by the United States Government.
The fact that, after an exhaustive test, twenty-eight sets of
wireless telephones have been ordered from the American
Radiotelephone Company for use in the navy, is a proof
that wireless telephony has already a commercial value.
The tests took place on board the battleships " Connecticut "
and ** Virginia," to which speech was transmitted from the
" Tennessee " and " Kentucky " at distances of from eleven
to twenty-five miles in the autumn of this year. The
articulation was clear and satisfactory even up to this
distance.

Telephony has, of course, some important advantages
over telegraphy, particularly as regards its use by unskilled
operators and as to speed. It has the disadvantage of
being rather more liable to error, since the words are not
spelled out letter by letter as in telegraphy, and in that no
form of automatic record is practicable.

One advantage of wireless telephony over wireless

APPENDIX. 199

telegraphy is that atmospheric discharges do not inter-
fere to nearly as large an extent. The reason for this is
that there is no difficulty in distinguishing the voice even
though there is a very considerable amount of extraneous
noise going on — it is done every day in ordinary and in
telephonic conversations. The conditions are not the
same in telegraphy, where, if a recorder be used, every
electrical impulse arriving at the receiver makes its mark,
whatever be its origin. If a telephone be used as a tele-
graphic receiver, strays (atmospheric discharges) may some-
times be distinguishable from signals, particularly if the
sparking of the transmitter is so rapid and regular as to
give out a definite tone by which the signals may be
differentiated from the strays. The distinction is not,
however, so easy as in telephony.

Among recent achievements in wireless telephony
may be mentioned Professor Fessenden's experiments in
America, of which details are given below, and the Poulsen
Company's demonstration of the transmission of speech
over a distance of about fifty miles in the neighbourhood of
Berlin. Details of the latter have not been published, but
there is little doubt that the arc is used as H.F. current
generator, and that the control is by means of a micro-
phone inductively coupled to the supply circuit. A
successful demonstration of wireless telephony between
ship and shore was given by the De Forest Company at a
regatta on Lake Erie this year, when communication was
maintained all day over a distance of about five miles.

Recent Advances in Theory. — Dr Barkhausen's mono-
graph on the production of electrical vibrations, published
at Leipsic in July, contains a very full and complete
account of the theory of the various methods of producing
electrical vibrations, and in particular of the vibrating arc.
His curves, showing the different types of oscillation which
have been alluded to in Chapters XIII., &c., indicate very
clearly the passage of one type into another, and the
mathematical analysis which accompanies them expresses

200 APPENDIX.

very exactly the results of experiment. Among other
deductions, the following are of special interest to wireless
telephonists: — (i) "The energy given to the oscillations
increases with the square of the difference between the
voltage at which the arc strikes and that at which it bums,"
Another proposition of importance is that (2) " The con-
dition for a high frequency, and also for the production of
oscillations which are capable of inducing resonance, is
that the arc shall only remain extinguished for a very
short time." For practical purposes, we have the statement
that (3) " High frequency oscillations which are capable
of exciting resonance and at the same time of transmitting
considerable energy, are only obtained when the striking
voltage attains a high value in as short a time as possible
(a small fraction of the total period) after the extinction of
the arc." Hence the advantage of using metal electrodes
which cool rapidly, and of a magnetic or air blast which
cools the electrodes by causing a draught and blowing
away the ionised gases, or of an atmosphere of hydrogen,
which has a very high rate of diffusion. These actions are
more particularly important in that they ensure that each
time the arc is struck it shall be at a new place on the
electrode, which is still cold, and where there is as yet no
column of ionised gas. To the conditions given above
must be added that for the stability of the oscillation,
which is that (4) " The striking voltage, after it has very
quickly risen to a high value, must not further increase."
Another important observation is that (5) " The arc should
not be allowed to strike in the reverse direction, since the
conditions are then such as conduce to an irregular action."
This phenomenon may be prevented by the use of unlike
electrodes or by heavy damping.

Signor Alfredo Montel has published an account of
the calculation of a radio-telegraphic station using per-
sistent waves, in L Elettricista (Rome), No. 13 of 1907.
His results, which include actual numerical calculations,
are, of course, applicable to a telephonic station. The

APPENDIX. 20 1

paper is, however, too full of detail to render a short
abstract of any value. Those who are interested should
therefore refer to the original.

Details of Professor Fessenden's Work. — In con-
clusion, I shall give some details of Professor Fessenden's
recent inventions, with extracts from a memorandum
which he has kindly sent me, and from an independent
expert's report on some tests of his wireless telephone.

Heterodjrne Receiver. — One of the most interesting
of Professor Fessenden's many inventions is what he has
called the " Heterodyne " receiver, which is an ingenious
adaptation of the ordinary Bell telephone receiver to the
purposes of wireless telephony. He was led to its inven-
tion by a consideration of the great inefficiency of even the
most sensitive of detectors, and of their insensibility as
compared with a telephone. Thus, while a liquid barretter
or a magnetic receiver will give an indication with between
yJiy and Yuiny of an erg, an ordinary telephone will pro-
duce an audible sound with less than loooo Triy of an erg.

The Heterodyne receiver consists of two small coils of
wire, one of which is wound round a fixed core of very
fine iron wires ; the other, whose plane is parallel to that
of the first, is attached to a mica diaphragm. A high
frequency current from a local source is maintained in the
first coil, while the second is traversed by the current from
the receiving aerial. The frequency of the local current is
kept constant and within a few per cent, of the normal
frequency of the transmitter, and, therefore, of the received
current. Thus, when the frequency or amplitude of the
transmitted current is altered by the action of the voice
in speaking, the mechanical force between the two coils of
the receiver varies in like manner, and the result is a repro-
duction of the sound by the mica diaphragm.

An important point, noticed by a telephone expert at a
test of Professor Fessenden's apparatus, is that, in wireless
telephony, there does not appear to be any distortion of
sounds with increase of distance, as is the case in all line

202 APPENDIX.

wires. It should therefore be possible to telephone wire-
lessly to very much greater distances than can be attained
by wire as soon as proper means have been devised for
the radiation of a larger amount of energy.

Historical Notes by Professor Fessenden. — In
December 1899 a rotating commutator was constructed
for me by Mr Brashear, according to my design. This
ran in oil and gave between 5,000 and 10,000 breaks per
second.

This was not tested for wireless telephony until October
and November of 1900, on account of other apparatus not
being ready. In November 1900 speech was for the first
time transmitted by electro-magnetic waves over a dis-
tance of one mile at Rock Point, Md.

Articulation was not very good, although understand-
able, on account of the hissing noise due to irregular
sparks. This was partly overcome by using a discharge
gap consisting of a platinum - iridium sheet and an
aluminium point.

The possibility of generating waves by a high frequency
alternator was investigated, with favourable results, and the
design of a high frequency alternator begun. (See U.S.
patent, No. 706,737, filed 29th May 1901.)

In the meantime the Elihu Thomson singing arc was
investigated. It was found that high frequencies could be
generated by it, but that the intensities and frequencies
varied greatly. The arc was used under compression.
(See U.S. patent, No. 706,741, filed 5th November 1901.)

It was found that, by introducing resistance and making
other changes, a constant frequency and intensity could be
obtained. (U.S. patent. No. 706,742, filed 6th June 1902,
figure 10, and the divisional case 730,753, filed 9th April
1903, more particularly page 2 of the latter.)

Successful results having been obtained, the method
was patented and published. (See U.S. patent, No. 706,747,
filed 28tb September 190 1.)

In 1903 the first high frequency alternator was com-

APPENDIX.

203

pleted, and much belter results were obtained as regards
articulation.

About the middle of 1906 the difficulties from the
hissing of the arc had been practically overcome, and tele-
phonic communication was being maintained between
shore and a small schooner up to distances of twenty miles
from shore.

In the fall of 1906 a high frequency alternator giving

Fu;. 140.
Multiple Arc Apparatus with Rotary Electrodes,

frequencies up to 80,000 was completed, and this also was
used in communicating to the schooner.

Meantime telephonic transmitting and receiving relays
had been designed and completed and a station equipped
at Plymouth, eighteen miles by road or eleven miles on a
straight line from Brant Rock, and speech was being
transmitted from a local wire line to the wireless station,
and there relayed wirelessly to Plymouth, and then relayed
but again to another local circuit.

Apparatus tests were made in the presence of engineers

204 APPENDIX.

about this time. For a report of the result of such a test
see American Telephone Journal editorial, pa^^e 75, dated
2nd February 1907.

A test was made by a representative of the Bell Tele-
phone Company (see below).

Lately we have been communicating between Brant
Rock and another station which we erected in New York
City, a distance of nearly two hundred miles. In these
latter tests about two hundred and -fifty watts were used.

For other work in wireless telegraphy see U.S. patent,
No. 793,649, filed 30th March 1905.

There are a number of patents on multiplex telephony,
/.^., sending and receiving a number of messages simul-
taneously from the same station, but these have not been
published yet.

We have recently succeeded in constructing and operat-
ing high frequency alternators giving an output of more
than two kilowatts at a frequency of 100,000 cycles, and
have under construction some turbine-driven alternators
giving about twenty kilowatts output at a frequency of
about 200,000 cycles.

You may be interested to have a description of one of
our designs for ship use. This consists of a field disc six
inches in diameter with three hundred teeth. The gap is
approximately one-eighth of an inch, and there are two
armature discs. This is driven by a small De Laval
turbine five inches in diameter and without any governor,
the governing being done by an electrically operated re-
ducing valve. The speed is 30,000 revolutions per minute.
The resistance of the armature is two ohms, and the volt-
age one hundred and fifty volts to two hundred volts.

The whole of the rotating parts are on a gyroscopic
mounting, so that when used on ship-board the rolling of
the ship will not cause the shaft to bend too much.

The operation of the plant is very simple, the operator
having no electrical connections nor spark gaps to look
after, but requiring merely to open a valve and bring his

APPENDIX. 205

dynamo up to speed. When this is done he is at liberty
either to telegraph or telephone by merely throwing over
a switch.

This apparatus produces no interferences on neighbour-
ing stations for obvious reasons, as the output is constant,
and what is known as the " scissors system " of sending is
used.

Wireless Telephone Tests at Brant Rock and

Plymouth, Mass.

(By an Expert of the Bell Telephone Company.)

Excerpts from a Description,

On Friday, 21st December 1906, I was present at a test
of wireless telephony, between stations at Brant Rock, and
Plymouth, Mass. The air- line distance between these
stations is eleven miles, passing almost entirely over water.
The tests were conducted by the National Electric Signal-
ing Company, under the personal supervision of Professor
R. A. Fessenden.

There were also present Professor Elihu Thomson of
the General Electric Company, and Messrs Keating and
Davis of the Associated Press.

Transmitting Apparatus and Circuits.

The transmitting station was located at Brant Rock,
employing as a radiating antenna the 400-foot steel tower
used in transatlantic signalling. In addition to the tower
proper, a sort of skeleton umbrella, composed of four
hollow cylinders of wire, depended from the top.*

The radiating antenna is connected to ground through
a tuning inductance, the secondary of a high frequency
transformer, and a granular carbon button, which is either

* See Handbook of Wireless Telegraphy, by J. Erskine-Murray,
p. 170 (Crosby Lockwood, London, 1907)-

2o6

APPENDIX.

used directly in a transmitter, or as an element of a tele-
phone repeater. In the primary circuit of the transformer
is connected the high frequency alternator.

I consider this alternator a most remarkable piece of
apparatus. It is a complete controversion of the fre-

FiG. 141.
H.F. Alternator Armature ; a fixed disc of Mordey Type.

quently made statement that a high frequency alternator
of any considerable output is an impossibility.

No less an authority than Professor J. A. Fleming has
considered an alternator of sufficiently high output and
frequency for wireless communication a practical^ impos-
sibility.

This alternator is a small machine of the Mordey type,

APPENDIX.

207

having a fixed armature in the form of a thin disc, or ring,
and a revolving field magnet with 360 teeth, or polar pro-
jections. At a speed of 139 revolutions per second, an
alternating current of 50,000 cycles per second and a
terminal E.M.F. of 65 volts is generated. The maximum

Fig. 142.
Field Magnet Disc of H.F. Alternator.

output of the alternator at the above frequency is 0.3
kilowatt.

Very little difficulty seems to have obtained in running
the machine at so high a speed, a simple flat belt drive
being used, and a thin self-centring shaft entirely obviates
excessive vibration and pressure on the bearings.

Although, as above stated, the maximum output of the

208 APPENDIX.

alternator is 0.3 kilowatt, measurement with hot wire in-
struments shows that, when connected in the transmitting
circuit, only about 36 watts is used. Of this energy, one-
third, or 12 watts, is radiated as electrical waves from the
antenna, the remainder, or 24 watts, is dissipated as heat in
the ohmic resistances of the transmitter button, tuning
inductance, and transformer secondary.

Owing to resonance, the E.M.F. of the antenna is much
higher than the terminal voltage of the alternator. A
measurement with electrostatic voltmeter indicates that
the potential is approximately 2,000 volts.

The transmitter button is located at a potential node,
and, when speaking, the potential fall across its terminals
is between 5 and 1 5 volts. The current flow, indicated by
a hot-wire ammeter, is about 2.1 amperes.

While transmitting speech wirelessly, the action of the
system is briefly as follows : — With the alternator running,
a steady alternating current, at a frequency of 50,000
periods per second, flows through the radiating circuit.
A resistance change in the transmitter button varies this
current, and, in proportion to this variation, the R.M.S.
potential of the antenna rises and falls. As the radiation
varies directly as the potential, the radiated waves also
vary in intensity in direct proportion to the resistance
changes in the transmitter button.

Receiving Apparatus and Circuits.

In this test the receiving station was located on the
water front at Plymouth. A sectional wooden mast, 170
feet high, carried a vertical fan of wires, branching at the
top in a manner similar to the transmitting station. The
receiving circuits differ in no wise from those employed in
wireless telegraphy. The receiving antenna is grounded
through a tuning inductance, and the primary of a trans-
former, in whose secondary circuit the detector was placed.

APPENDIX.

209

Test of Wireless Speech Transmission.

After inspection of the transmitting station at Brant
Rock, Mr Keating and myself went to the Plymouth
station, arriving there about 3.30 P.M. After a slight

Fig. 143.
Receiving Relay Amplifying Fifteen Times.

delay the alternator at Brant Rock was started, and a
phonograph selection — a violin solo — was transmitted.
This was by repeater, the phonograph talking into a
transmitter, and from thence over a short line to the
windings of a " Differential Relay," one of whose buttons

2IO APPENDIX.

was included in the radiating circuit. At Plymouth this
could be heard fairly well at times, the characteristic timbre
of the violin coming out about as well as the imperfections
of the phonograph record would permit. Apparently
much difficulty was experienced with the repeater button
packing, for the variations in received volume were enor-
mous. During this selection, some one at Brant Rock
would occasionally tap or jar the repeater button, pro-
ducing thereby a loud sound in the Plymouth receivers,
and for a few seconds thereafter greatly improving the
transmission.

After another phonograph selection, Mr Davis, at Brant

Fig. 144.
Receiving Transformer in which rrimary and Secondary, and also their Dis-
tance Apart, i.e.. Coupling, may be varied for Tuning Purposes.

Rock, talking through the repeater, sent a short message
to Mr Keating at Plymouth, which was correctly received,
barring an error in a single word. While a distinct im-
provement over the phonograph, a large variation in
received intensity still existed. The repeater was then
discarded, and Professor Fessenden talked some ten
minutes to me, using a directly connected transmitter.
Although still variable in volume, the quality of this
transmission was most excellent, and I had not the
slightest difficulty in following everything he said. It
was even possible to distinguish fairly well between single
consonant letters, such as " B " and " P." A high-pitched

APPENDIX.

211

whistle, certainly over 5,cxx) periods per second, came
through clearly, and even loudly.

Taken as a whole, I should consider the speech trans-
mission as distinctly commercial.

Fig. 145.
Variable Condenser for Tuning Purposes.

Detail of Accessory Apparatus Employed.

The buttons employed in both the repeater and the
direct transmitter were similar to those of our radiophone
transmitter, heavy platinum-iridium faced electrodes, and a
granular carbon filling, 40-60, being used.

The repeater, or " Differential Relay," is a somewhat

212 APPENDIX.

novel form. While at Brant Rock several tests of this
repeater were made, such as talking into it over a " zero "
line, with a loud-speaking receiver directly connected to
the other side. Watch ticks, phonograph selections, and
the voice were amplified apparently several times, but the
conditions of these tests were not such as to show whether
or no the device was in any way sensitive to the feeble
incoming transmission. Unfortunately, but one repeater
was available, so that no tests could be made with it at the
receiving end.

Possibilities of Present System and
Apparatus.

Professor Fessenden told me that the apparatus em-
ployed was not, at the time of the test, operating at any-
where near its maximum efficiency.

The alternator, although operating at 50,000 cycles, was
designed f6r 100,000. At this frequency, the radiation
from the antenna, other factors remaining the same, is
greatly increased. As the radiation increases with the
fourth power of the frequency, this doubling of the
periodicity would increase the radiation sixteen-fold, and,
as the range varies with the square root of the radiation
intensity, the distance of communication would be increased
four times. This would mean about forty miles with the
present equipment

Equally, improvement in transmitter operation would
give a decided gain. It was stated by Professor Fessenden,
and seemed probable to me, that the present transmitter
only varied about S per cent, of the total radiated energy.
With another form of transmitter, not used in any of the
tests, a variation of 50 per cent, is claimed. This improved
form is merely a condenser telephone transmitter placed in
shunt to the radiating circuit, the small capacity variations
resulting from the vibration of one of the plates throwing
the radiating circuit in and out of tune with the alternator.
In theory, at least, this form of transmitter should give the

APPENDIX. 213

results claimed. If it did in practice, it would mean an
increase in the energy telephonically modulated of ten
times, and an increased range of three times.

Probably, with the apparatus I saw in operation worked
to its maximum efficiency, a range of about 100 miles
might be reached, preserving commercial transmission.

Possible Developments of the System.

It is difficult, with our present knowledge of high fre-
quency alternators and other mechanical sources of steady
high frequency current, to assign a definite limit to the
amount of energy that can be generated and radiated.
Probably several kilowatts can be generated by mechani-
cal sources of high frequency current, sources resulting
from a simple development of the present devices. How
much of this energy can be effectively telephonically modu-
lated is a still more difficult question. Where a direct
action upon the high frequency current is concerned, it
seems that 100 watts was an upper limit of the micro-
phonic type of transmitter. This amount of energy, in the
form of telephonically modulated electrical waves, would
probably give commercial transmission over several hun-
dred miles, under favourable conditions. The electrostatic
transmitter, which depends upon an indirect action upon
the energy, may be capable of varying several kilowatts,
and so increasing the range to a thousand miles or more.
This, however, is mere speculation.

It is my opinion that ranges of several hundred miles
are now possible, but a considerable amount of develop-
ment work will be required before these are attained.

The question of range, although important, seems to
me subordinate to the question of

Simultaneous Working of Several Stations.

As stated under the possibilities of the present system
and apparatus, the receiving station was not sharply tuned.

214 APPENDIX.

Yet, even with the circuits employed, I found by experi-
ment that a variation of 5 per cent in the tune of the
receiving circuit reduced the vohime of receiving by some
90 per cent Assuming that the present range of fre-
quency available and economical from mechanical sources
is from 50,000 to 1 50,000 cycles per second, something less
than ten stations could exist harmoniously in a given
district. The number would of course depend upon the
permissible cross-talk, and this, in turn, would depend upon
the distances between stations as well as the differences
in frequency. Save in a specific case, with these distances
known, it would be impossible to define, even approxi-
mately, the number of simultaneous conversations that
might wirelessly exist

It would seem that there were three distinct sources of
high frequency current available for wireless telephony.
The first of these is the alternator already described. The
second is the " singing arc," which, according to Fessenden,
is capable of development into a fairly steady and definite fre-
quency source. The third source is a " condenser dynamo "
which is simply a rapidly variable condenser, formed of
radially slotted discs, revolving in opposite directions in
such manner as to vary the capacity from disc to disc some
hundred thousand or more times a second. Connected
with a source of direct current, this rapid variation in
capacity creates a high frequency current. According to
Fessenden's calculations, a very compact machine, deliver-
ing about two kilowatts of high frequency current, and of
extreme constructional simplicity, can be made in this
manner. No machine of this type was shown, and it did
not appear that it had been tested on any practical scale.
From theory, however, the service should be operative in
the manner claimed, and form a simple and cheap source
of high frequency current

Boston, 24th December 1906.

MVERSITY

ADDENDA AND CORRIGENDA

To page

xiii.— Chap. XVII. should be entitled "The Impure Duddell
Phenomenon."

99, Note.—Yo\ " Weselius," read " Wesselius."

loi, Note.— For " Reinart," read " Reinartz."

103, Note,— Fox " 4. I. 07," read " 16. I. 07."

126, Note, — The damping factor, c ^ should read e ^L •

142. — Chap. XIII. describes, «>i/^r «//a, the Pure Duddell Pheno-
menon. ^

145, Note.—Stt also P. Bary, Eclair. Electr., li., p. 45, 1907.

'54i Note.—Stt also lecture by Poulsen on " System for Producing
Continuous Electric Oscillations,^ Transactions of the Inter-
national Electric Congress at St Louis (1903), ii., p. 963,
1904-05.

155, Note.— On the influence of gases and of cooling of the elec-
trodes, see Simon and Malcolm, Phys. Zeitschr.^ viii., p. 471,
1907, and Jahrbuch d. drahtlose Telegr. u. Teieph.^ i., p. 33,
1907.

161. — Fig. 120A should be entitled " Adjustable Battery of Arcs of
the Gesellschaft fiir drahtlose Telegraphie" (Berlin) — not
Ruhmer's.

164, Figs. I22A and \22B. — Ruhmer's high-tension arc H.F. current
generator differs from others in that the length of the arc is
maintained constant by an ingenious but simple arrangement
of the electrodes. These are in the form of wires which are
moved with a slow and constant velocity, so that the arc is
formed between points on the sides of the wires, fresh portions
of which are constantly being brought forward to where the
arc bums, thus keeping the arc-length constant, and providing
a cooler electrode than can be otherwise attained (see Appen-
dix, p. 200).

166, Note. — See also Fleming, lecture at the Royal Institution,
London, 24th May 1907 ; and Tissot, Report to TAssoc. fran-
gaise pour I'Avancement des Sciences, August 1907.

173, Note. — See also Austin, The Electrician^ p. 794, 1907, on a
thermo-electric detector.

174, — Chap. XVII. should properly be entitled "The Impure
Duddell Phenomenon." The pure Duddell phenomenon is
treated of in Chap. XIII.

185, see also E. Ruhmer, German patent, application R. 23,796,
Class 2i«, of 31st December 1906, published 22nd July 1907.

215. — Zacharias u. Heinicke, " Practisches Handbuch der draht-
losen Telegraphie u. Telephonie," Wien u. Leipzig, 1907.
Partheil, " Die drahtlose Telegraphie u. Telephonie,*' 2
Aufl., Berlin, 1907. Stockhausen, " Der eingschlossene Licht-
bogen bei Gleichstrom," Leipzig, 1907. Zenneck, " Electro-
magnetische Schwingungen und Drahtlose Telegraphie,"
Stuttgart, 1905.

BIBLIOGRAPHY.

Bell, Alexander Graham. Das Photophon. Leipzig, 1886.
BiEGON VON CzuDNOCHOWSKi, W. Das elcktrische Bogenlichts.

Leipzig, 1906.
BiRRENBACH, H. Thcorie und Anwendung des elektrischen

Bogenlichts. Hannover, 1903.
Heinke, C. Handbuch der Elektrotechnik. Leipzig, 1904.
Jentsch, Otto. Telegraphic und Telephonie ohne Draht.

Berlin, 1904.
Mazzotto, D. Telegraphie und Telephonie ohne Draht.

Miinchen, 1906.
MoNASCH, B. Der elektrische Lichtbogen. Berlin, 1904.
Nerz, F. Scheinwerfer und Fernbeleuchtung. Stuttgart, 1 888.
Prasch, a. Die Telegraphie ohne Draht. Wien, 1902.
Prasch, a. Die Fortschritte auf dem Gebiete der drahtlosen

Telegraphie. Stuttgart, 1905-6.
Radiophone, The. St Louis, 1904.
RiGHi, A., und Dessau, B. Die Telegraphie ohne Draht.

Braunschweig, 1903 und 1907.
RuHMER, E. Das Selen und seine Bedeutung fur die Elektro-
technik. Berlin, 1902.
Tesla, N. Untersuchungen uber Mehrphasenstrome und uber

Wechselstrome hoher Spannung und Frequenz. Halle,

1895-

Araeric. Teleph. Jour. — American Telephone Journal (New York).
Ann. d*Elektrotechn. — Annalen der Elektrotechnik (Leipzig).
Ann. d. Phys. — Annalen der Physik (I-,eipzig).
Arch, d'filectr. Med. — Archives d'felectricite medicale (Bordeaux).
Beiblatter — Beiblatter zu den Annalen der Physik (Leipzig).

2l6 BIBLIOGRAPHY.

Berichte der Erlanger physikalisch - medizinischen Sozietat

(Erlangen).
Bulletin de la Societe fran9aise de Physique (Paris).
Comptes Rendus — Comptes Rendus Hebdomadaires des Seances

de TAcademie des Sciences (Paris).
D.R.P. — Deutsches Reichspatent
Eclair, ifelectr. — I/6clairage 6lectrique (Paris).
Electrical Engineer (New York).
Electrical Review (London).
Electrical Review (New York).
Electrical World and Engineer (New York).
Electrician (London).
6lectricien (Paris).
Elektrotechniker (Wien).
Elettricista (Rome).
Engineering (London).
English Mechanic (London).
E.T.Z.— Elektrotechnische Zeitschrift (Beriin).
Fur alle Welt (Beriin).

Jahrbuch der Schiflfbautechnischen Gesellschaft (Berlin).
Journ. de Phys. — Journal de Physique Theorique et Appliqu^e

(Paris).
Journal der russ. phys. Chem. Gesellschaft.
Journal of the Proceedings of the Institution of Electrical

Engineers (London).
Journal of the Society of Telegraph Engineers.
Mechaniker (Berlin).
Nature (L.ondon).
Nuovo Cimento (Pisa).
Phil. Mag. — The London, Edinburgh, and Dublin Philosophical

Magazine and Journal of Science (London).
Phil. Trans. — Philosophical Transactions of the Royal Society of

London.
Phys. Zeitschr. — Physikalische Zeitschrift (Leipzig).
Pogg. Ann. — Poggendorff, Annalen der Physik (Leipzig).
Proceedings of the American Institution of Electrical Engineers.
Proceedings of the Physical Society of London.
Proceedings of the Royal Society (London).
Rev. ind. — Revue industrielle (Paris).

BIBLIOGRAPHY. 217

Rendiconti dei Lincei — Rendiconti della Reale Accademia del

Lincei (Rome).
Scientific American (New York).
Tijdschrift v. Geneeskunde.
Technische Rundschau (Berlin).
Western Electrician (Chicago).
Wied. Ann. — Wiedemann's Annalen der Physik und Chemie

(Leipzig).
Zeitschr. f. d. phy. u. chem. Unterricht— Zeitschrift fur den

physikalischen und chemischen Unterricht (Berlin).
Zeitschrift fur Elektrotechnik und Maschinenbau (Wien).
Zeitschr. f. Schwachstromtechn. — Zeitschrift fiir Schwachstrom-

technik (Miinchen).

NAME INDEX.

Abraham, H., iio, 184
Armstrong, 83
Ascoli, 128, 143
Ayrton, H., 145, 146, 155
Ayrton, W. E., 197

Bell. A. G., 8, 10-14, I9f 30, 31

Benlscbke, G., 192

Blondel, A., no, 119, 129, 145, 177,

182, 184
Braun, F., 27, 99, 124, 127
Brown, 102
Brown, S. G., 166

Campos, 153, 159, 170

Cassuto, L., 155

Chladni, 39

Clark, L., 3

Collins, A. F., 83, 94, 95

Corbino. 143, 178

Cram, £. R., 31

De Forest, L., 173

De la Rive, 183

Dolbear, A. E., 93

Dolezalek, F., 134

Ducretet, 82

Duddell, W., 25, 99, 134, 142, 145,

147, 150, 160, 175, 178, 182 184,

187, 191
Dussaud, 78

Ebert, 77

Edison, Tb. A., 94, 196

Eisenstein, S., 117, 119, 121, 124, 151,

158
Engisch, 83
Evans, C. J., 89
Ewing, 133

Fabry, 144

Faraday, 9

Feddersen, 130

Fessenden, R. A., 103, 128, 130, 135,

138, 140, 153, 158, 170, 173, 180,

181, 196
Fitzgerald, G. F., 184
Fleming, J. A., 173
Franz, R., loi
Frith, 187

Gavey, 89, 91

Gesellschaft fUr Drahtlose Telegraphic

(Berlin), 116, 161, 163, 170, 174
Giltay, J. W., 14, 16, 20, 22
Grandq'uist, G., 144, 155
Gray, E., 2

Harden, J., no
Hahnemann, W., 159, 174, 189
Hayes, H. V., 30, 31
Heinke, C, 131, 143
Hertz, H., 77, 130
Hewitt, C, 116, 179
Homemann, 172
Hutchison, M. R., 89

Jamieson, A., 14
Janet, 143

Kaufmann, 145
Kerr, 9
Konig, 14
Koepsel, 152
Krelle, O., 62

Leblanc, M., 134
Lecher, 142
Levy, 27
Lodge, 132
Lonardi, 102, 107

220

NAME INDEX.

M«Carty, F. T.,99

Maiche, L., 82

Majorana, Q., 107, 113, 118

Maisel, S., 145, 178

Manzetti, 143, 178

Marconi, G., 96, 99

May, 3

Mazzotto, D., 159

Mercadier, 11

Monasch, B., 155, 161

Hosier, H., 85, 87, 99, 118, 150, 159,

185
Munday, A. J., 2
Musits, R., 83

Neilson, 102
Ncrz, F., 62
Nussbaumer, O., 99* 118, 150

Orling, 83

Perry, 76

Penkert, W., 142

Pierce, W., 116

Plisner, 92

Poulsen, v., 154, 155, 156, 158, 160,

163, 174, 181. 191, 192
Preece, W. H., 89, 91

Rautenkrantz, J., 131

Reich, M., 32, 116, 124, 137, 138, 140,

145, 179
Remartz, J., loi
Reithoffer, M., 189
Righi, A,, 154, 181
Rodgers, 187
Ruedenberg, R., 135

Ruhmer, E., 2, 16, 19, 23, 25, 29, 32,

33. 36, 43, 72, 76, 83. 112, 134,
160, 167, 178, 184, 190, 192

Ruppin, W., 1 01

Salomons, D., 133

Schmidt, K. E. F., 133

Schuckert, 49

Sella, 77, 78

Short, I

Siemens, W., 4

Simon, H., Th., 20, 23, 2S, 26, 32, 33,

34, 99, 116, 124, 125, 137, 138,
145, 148, 150, 154, 173, 179, 181,
191

Smith, W., 2
Stark, J., 155
Steinmetz, C. P., 132
Szczepanik, J., 103

Tainter, S., 4, 6, 8

Tesla, N., 131, 132, 196

Thomson, E., 113, 132, 142, 179, 180

Thomson, W. (Kelvin), 114, 178

Thury, 134

Tissot, 143, 173

Valbreuze, 178
Valle, 92
Vogel, H. C, 58
Vossnack, E., 135
Vreeland, K., 194

Wehnelt, 190
Weintraub, 178
Wertheim-Salomonson, 143
Weselius, H., 99
Wiedemann, 77
Wien, M.. 127, 133, 135
Wilson, E., 89

Zickler, K., 77, 103

SUBJECT INDEX.

ABSORPTION of heat rays in air,
71
of light of different wave-lengths in

air, 71, 73» 78
Acetylene flame transmitter, 16

signal lamp, 49
Acoustic control of arc, 23, 84
Active arc, 192

length of arc, 156
Advantages of light-telephony, 74
Air blast, 113, 180, 183, 185, 192

spark gap, 124, 179, 181
Aluminium electrodes, 113, 163
Alternate current curve form, ill, 119,

130

current, rectangular curve, 119

current siren, 133

current transformer, 114, 138
Alternator, 137, 138, 206
Aperiodic discharge, 127
Arc characteristic, 145-148, 191

discharge, 99, no, in, 190

generator, 154, 159, 168, 185, 190,

I93» 199

hysteresis, 147

interruption, 185, 191

interruptor, 185, 189, 19 1

-lamp concert, 26

length, influence of, 64, 166

as microphone, 29

as telephonic receiver, 23

pianoforte, 144

speaking. See Speaking Arc.

voltage, influence of, 64
Articulation in wave telephony, 170
Audibility in electric wave telephony,
168

in light-telephony, 55, 6^, 68

in radiophony, 170
Audion, 173

BALANCING cells, 23
Berliner's granular microphone,
27
Best conditions of speaking arc for radio-
phony, 29, 38, 60
size and resistance of selenium cell
for light-telephony, 69
Blast-magnet, 170, 180, 183, 184, 187,

189, 192
Bolometer, 76
Braun*s circuit, 99, 127, 135
tube, 181, 189

CAPSULE, manometric, 14, 16, 17
Carbonic acid gas, 113
Cathode ray oscillograph, 168
Characteristic of the arc, 146, 148
of the arc-interruptor, 191
of the musical arc, 191
of the Poulsen generator, 191
Characteristics of selenium cells, 70
Choking coil, 23, no, 143, 156, 182
Cinematograph, 36
Cinematographic records, 112, 115,

Closed circuit wireless telephony, 2,

79-87
Colour -sensitive selenium cells, 73
Complete station for light telephony, 53
Condenser dynamo, 135
Conductivity of spark gap, 125, 129
Construction of selenium cells, 41
Control by microphone current, 96, 170
of the aerial wire current, 129
of the field of a D.C. dynamo, 99,

136, 170
of the oscillating circuit, 129, 184
of the supply current, 99, 129, 151,
184

222

SUBJECT INDEX.

Cooling of electrodes, 155, 163, 174,

181, 192
Copper electrodes, 155, 160, 163
Cored carlions, 27, 187
Coupling, 23, 138, 173, 194
Critical current, 156, 160
Current curve, 190

DAMPED oscillations, 130
Damping, 105, 127, 180

Dark rays, 76

Deckert's microphone, 90

Demonstration apparatus for light-tele-
phony, 18, 21, 54

Direct current, high tension, supply to
spark gap, 124, 128

Disruptive discharge, 177, 179, 180,
182

Discharge voltage, no, 127, J29

Discharges in series, 119, 127, 128

Disadvantages of light -telephony, 75
of wave telephony, 195

Divergence of searchlight beam, 63

Divided arc, 160

Duddell phenomenon, 128, 142, 145,
148, 174, 182, 187, 191

Duration of charging, 126

Dynamic characteristic of the arc, 146,

191
Dynamo machine, 26

ELECTRIC coupling, 23
motor boat, 45
Electrod3mamic theory of discharge in

gases, 147
Electrolytic cells, 97, 168, 172
Electromagnetic induction, 89
Electromotograph telephone, 94
Electrostatic induction, 92
Energy in oscillating circuit, 174
Exhibition, Chicago, 10, 11

of electrical novelties (Berlin), 42,

185
of electrical novelties at Madison

Square
motor-boat (VVannsee), 43
St Louis, 31, 67, 89
Extinction of arc, 188, 191

FIELD magnet control, 26, 99, 137
Film, 36, 38
Filtration of heat rays, 71
Flame arc carbons, 27, 73

Fluorescent bodies, 78

screen, 190
Fog, 68, 76

Forced vibrations, 183, 185, 188, 192
Foucault currents, 130
Frequency variations of electric waves,

104, 132, 140
Future of electric wave telephony, 194,
196
of light-telephony, 74

GASOLENE vapour, 15
Geissler tube, 181
Gimbals, searchlight on, 67
Glass parabolic mirror, 53
Gouraudphone, I
Granular carbon microphone, 27

HAMMER break, 20
Hard selenium cells, 71
Heat conductivity of electrodes, 148,

I55» 156
Hertz*s phenomenon, 77
Heterodyne receiver, 173, 201
High frequency alternator, 131, 138,

174, 202, 206, 212
High tension arc, 128, 163, 167, 178
Hydrogen atmosphere, 154, 166, 192
Hysteresis curve, 147, 148, 177, 191

IMPORTANCE of electric wave
telephony, 194, 196
of light-telephony, 75
Impregnated carbons, 27
Impure Duddell phenomenon, 177, 178,

180, 182
Inactivity of arc, 150, 170, 192

of spark, loi, 113, 124
Induction telephony, 2, 88-95
Inductive coupling, 23
Influence of the supply voltage on
selenium cells, 70
of the transparency of the air, 67
Intensity variations of electric waves,

102, 129, 137, 140
Intermittent partial discharges, 176
Interruption phenomena, 191
Interruptor cnaracteristic, 191
Invisible rays, 76

[ OULEAN heat, 26

SUBJECT INDEX.

223

l^ITES, 93

LAWS of radiation, 28
Length of arc for Diiddell pheno-
menon, 145
of arc in impure Duddell pheno-
menon, 176
Light filter, 73, 76
Light-electric telegraphy, 77, 103
Light-telephony, 2, 14-19, 20-78
Limitation of supply current by choking

coil, III
Logarithmic decrement, 127
Loose coupling, 173
Loudness of the speaking arc, 22, 26

MAGNETIC blast, 113, 183, 185,
192, 193

detector, 97, 107, 129
Magnetically influenced arc, 89, 156,

163, 170, 183-195
Manometric capsule, 14, 15, 22, 170

flame, 129
Map of Wannsee experiments, 48
Marconi transmitter, 96
Maxwell's theory, 88
Mercury arc, 115, 124, 179, 194

arc as interrupter, 1 15

vapour wave detector, 173
Metal electrodes, 159, 174
Microphone, i, 12, 22, 23, 25, 27, 30,

83, 89, 93

contact, 99

large current, 83
Mirror, focal length of, 64
Motor boat exhibition, 43
Mounting of selenium cells, 41
Multi- phase current, 119
Multiple arc generator, 160

spark discharge, 112
Multiplex light-telephony, 73

telephony, 194
Musical arc, 142, 175, 180, 184, 187,

191

XJICOL'S prism, 9

Non-arcing metals, 113

OPACITY of crystalline selenium.

Oscillating circuit, 99
Oscillation trains, 106, 1 16

Oscillations of an arc in a magnetic

field, 188, 190
Oscillatory discharge, 105, 135, 183
Oscillograph, cathode ray, 167
Oscillographic methods, 190

records, 144, 148, 175, 176, 188
Outfit for wave telephony, 170
Oxide coherer, 172

PARABOLIC mirror, i, 5, 18, 30,
41. 49» 58
Partial discharges, 114, 115, 118, 128
Photographophone, 36, 40
Photophone, 4, 6, 9, 14
Photophonic receiver, 30, 32

sender, 6, 10, 30
Photophonogram, 37
Porcelain core for selenium cell, 41
Portable light telephonic apparatus, 57

power station, 57
Poulsen generator, 154-158, 174, 181,

190
Practical uses of induction telephony,

uses of wave telephony, 196
Priority of invention of speaking arc, 31

RADIOPHONE, 10
Radiophony, 2, 3-78
Radiotelegraphic conference, 166
Range of hyarotelephony, 80, 83

of induction telephony, 90

of light-electric telephony, 78

of light-telephony, 75
Rates of sparking, iii, 115, 125
Receiving station, radiophonic, 8, 9

tube for light-telephony, 77
Resistance of selenium cells, 5
Resonance, 137, 185, 187
Rotating mirror, 168

SEARCHLIGHT, 31, 43, 49, 75
Secret conversation, light - tele-
phonic, 74
Selenium, 3

cells, 4, 15, 21. 30, 32, 38, 68, 73
cell, speed of action, 70
Self-decohering coherers, 97
Sensibility of selenium cells, 41, 42
Series arrangement of arc, 160
Single impulses, 180

-phase current, iii
Singing spark, 97, 102
Smoke, 77

224

SUBJECT INDEX.

Soot cells, 1 1

Sound propagation through air, 2
pro (ligation through water, 2
Spark coil, 96, 99, 102, 104, 109, 114,

telephony, 96-130
Speaking arc, 23, 26

arc as photophonic transmitter,
28,29

spark, 97, 102

trumpet, i
Stage arc lamp, 49, 53
Star connection, 120
Static arc characteristic, 146
Striking voltage, 176
Submarine signals, 2
Sun's rays, 6
Superposition of microphone current on

supply current, 60
Supply current for speaking arc in
light-telephony, 64

voltage for selenium cells, 69

TELEGRAPHONIC receiver, 173
Telegraphy, light-electric, 74
Telephone, loud-speaking, i
Telephony by electric forces, 77-214
by heat rays, 3-78
by light rays, 3-78
by ultra-violet rays, 77
Tesla transformer, 166
Theory of arc hysteresis, 147

of Poulsen generator, 154, 181,

190, 191, 199
of the speaking arc, 26
Thennophone, 10
Thermophonic receiver, n, 12

Thomson arrangement, 179, 180, 187
Thomson's formula, 114, 127, 178
Three-cornered circuit, 121, 123

-phase current, 119

-phase spark gaps, 121, 123
Time of arc striking, 126, 176
Torpedo-boat searchlight, 43
Trains of damped waves, 179-182
Transformer, 23, 26, 1 11, 114
Transmitter photophonic, 4, 6, 9, 10

for wave telegraphy, g6
Transparency of air, 55, 67

of ebonite, 76
Turbine interrupter, 104

ULTRA-VIOLET rays, 77
Undamped oscillations, 130
Undulating lignt rays, 30
Unsymmetrical spark gap, 181
Uses of electric-wave telephony, 194,

196

of light-telephony, 57

VACUUM tubes, 167
Valve spark gap, i8i
Variation of coupling, 138, 194

of transmitter frequency, 140
Visibility of searchlight beam, 75

WANNSEE experiments, 43
Wave telephony, 2, 96-195

^ INC electrodes, 113

^ OF THE '^^^-^

^NfVERSfTY

' fpnR\v^

Printed at The Darien Press, Edinburgh.

LIST OF WORKS

Electrical Science

PUBLISHBD AND FOR SALB BY

D. VAN NOSTRAND COMPANY,

23 Murray and 27 Warren Streets, New York.

ABBOTT, A. V. The Blectrfcal Transmission of Energy. A Manual for the
Design of Electrical Circuits. New Edition, revised and rewritten. With
many Diagrams and Engravings and Folding Plates. 8vo, doth. Net, $5.00.

ANDERSON, GEO. L., A.M. (Capt U.S.A.). Handbook for the Use of Electricians
in the operation and care of Electrical Machinery and Apparatus of the
United States Seacoast Defenses. Prepared under the direction of Lieut.-
General Commanding the Army. Illustrated. Svo, cloth. $3.00.

ARNOLD, E. Armature Windings of Direct-Current Dynamos. Extension and
Application of a general Winding Rule. Translated from the original German
by Francis B. DeGress, M.E. Illustrated. 8vo, doth. $2.00.

ASHE, S. W., and KEILET, J. D. Electric Railways, Theoretically and Practically
Treated — Rolling Stock — ^With Diagrams and Folding Plates. 12mo, cloth,
290 pp. Illustrated. Net, $2.50.

ATKINSON, A. A., Prof. (Ohio Univ.). Electrical and Magnetic Calculations. For
the use of Electrical Engineers and others interested in the Theory and
Application of Electricity and Biagnetism. Second Edition, revised. Illus-
trated. 8vo, cloth. Net, $1.50.

ATKINSON, PHILIP. The Elements of Dynamic Electridty and Magnetism.
Fourth Edition. Illustrated. 8vo, cloth.- $2.00.
Elements of Electric Lighting, including Electric Oreneration, Measurement,
Storage, and Distribution. Tenth Edition, fully revised and new matter
added. Illustrated. 8vo, cloth. $1.50.
Power Transmitted by Electricity and Applied by the Electric Motor, induding
Electric Railway Construction. Illustrated. Fourth Edition, fully revised
and new matter added. 8vo, cloth. $2.00.

AYRTON, HERTHA. The Electric Arc 8vo, doth. Illustrated. 479 pp. Net,
$5.00.

2 LIST OF WORKS 0-V ELECTRICAL SCIENCE.

BlGGSy C. H. W. First Principles of Electricity and Magnetism. DJustrated.
12mo, cloth. $2.00.

BLAKESLEY, T. H. Papers on Alternating Currents of Electricity. For the use
of Students and Engineers. Third Edition, enlarged. 12mo, cloth. $1.50.

BOTTONE, S. R. Electric Bells and All about Them. 12mo, cloth. 50 cents.

Electrical Instrument-Making for Amateurs. A Practical Handbook. En-
larged by a chapter on "The Telephone." Sixth Edition. With 48 Illus-
trations. 12mo, cloth. 50 cents.

Electric Motors, How Made and How Used. 12mo, doth. 75 cents. •

BOWKER, WM. R. Dynamo, Motor, and Switchboard Circuits for Electrical
Engineers: a practical book dealing with the subject of Direct, Alternating,
and Polyphase Currents. With over 100 Diagrams and Engravings. 8vo,
cloth. Illustrated. Net, $2.25.

CHILD, CHAS. T. The How and Why of Electricity: a book of information for
non-technical readers, treating of the properties of Electricity, and how
it is generated, handled, controlled, measured, and set to work. Also
explaining the operation of Electrical Apparatus. 8vo, cloth. Illustrated.
$1.00.

COOPER, W. R. Primary Batteries: their Theory, Construction, and Use. 8vo,
cloth, 324 pp. 131 Illustrations. Net, $4.00.

CROCKER, F. B., and WHEELER, S. S. The Practical Management of Dynamos
and Motors. Revised and enlarged. Illustrated. Sixteenth Thousand.
12mo, cloth. $1.00.

CROCKER, F. B. Electric Lighting. A Practical Exposition of the Art for the
use of Electricians, Students, and others interested in the Installation or
Operation of Electric-Lighting Plants. Volume I.: The Generating Plant.
Sixth Edition, entirely revised. 8vo, cloth. $3.00. Volume II.: Distrib-
uting System and Lamps. Fourth Edition. 8vo, doth. Each, $3.00.

DESMOND, CHAS. Electricity for Engineers. Part I.: Constant Current. Part
II.: Alternate Current. Revised Edition. Illustrated: 12mo, cloth. $2.50.

DIBDIN, W. J. Public Lighting by Gas and Electricity. With many Tables,
Figures, and Diagrams. 8vo, cloth. Illustrated. 537 pp. $8.50.

DYNAMIC ELECTRICITY; Its Modem Use and Measurement, chiefly in its appli-
cation to Electric Lighting and Telegraphy, including: 1. Some Points in
Electric Lighting, by Dr. John Hopkinson. 2. On the Treatment of Elec-
tricity for Commercial Purposes, by J. N. Shoolbred. 3. Electric-Light
Arithmetic, by R. E. Day, M.E. 18mo, boards. (No. 71 Van Nostrand's
Science Series.) 50 cents.

EWING, J. A. Magnetic Induction in Iron and other Metals. Thurd Edition, re-
vised. Illustrated. 8vo, cloth. $4.00.

FISHER, H. K. C, and DARBY, W. C. Students Guide to Submarine Cable Testing.
Third Edition, new, enlarged. 8vo, cloth. Illustrated. Net. $3.50.

FISHER, W. C. The Potentiometer and Its Adjuncts. 8vo. cloth. Net, $2.25.

LIST OF W'ORKS ON ELECTRICAL SCIENCE, 3

FISKE, BRADLEY A., Lieut, U.S.N. Electricity in Theory and Practice; or,
The Elements of Electrical Engineering. Tenth Edition. 8vo, cloth. $2.50.

FLEMING, J. A., Prof. The Altemate-Current Transformer in Theory and Prac-
tice. Vol. I.: The Induction of Electric Currents. 500 pp. Fifth Issue.
Illustrated. 8vo, cloth. S5.00. Vol; II.: The Utilization of Induced
Currents. Third Issue. 594 pp. Illustrated. 8vo, cloth. $5.00.
Electric Lamps and Electric Lighting. 8vo, cloth. $2.50.

FOSTER, H. A. Electrical Engineers' Pocket Book. With the Collaboration of
Eminent Specialists. A handbook of useful data for Electricians and
Electrical Engineers. With innumerable Tables, Diagrams, and Figures.
The most complete book of its kind ever published, treating of the latest
and best Practice in Electrical Engineering. Third Edition, revised. Pocket
size, full leather, 1000 pp. $5.00.

GORE, GEORGE, Dr. The Art of Electrolytic Separation of Metols (Theoretical
-and Practical). Illustrated. 8vo, cloth. $3.50.

GRAY, J. Electrical Influence Machines: Their Historical Development and
Modem Forms. With Instructions for making them. Second Edition,
revised and enlarged. With 105 Figures and Diagrams. 12mo, cloth. Illus-
trated. $2.00.

GUILLEMIN, AMEDEE. Electricity and Magnetism. Translated, revised, and
edited by Prof. Silvanus P. Thompson. 600 Illustrations and several Plates.
Large 8vo, cloth. $8.00.

GUY, ARTHUR F. Electric Light and Power. Giving the result of practical ex-
perience in Central-Station Work. 8vo, cloth. Illustrated. $2.50.

HAMMER, W. J. Radium, and Other Radio-active Substances; Polonium, Actin-
ium, and Thorium. With a consideration of Phosphorescent and Fluo-
rescent Substances, the properties and applications of Selenium, and the
treatment of disease by the Ultra-Violet Light. With Engravings and
Plates. 8vo, cloth. Illustrated. $1.00.

HASKHfS, C. H. The Galvanometer and its Uses. A Manual for Electricians
and Students. Fourth Edition, revised. 12mo, morocco. $1.50.
Transformers: Their Theory, Construction, and Application Simplified. Illus-
trated. 12mo, cloth. $1.25.

HAWKINS, C. C, and WALLIS, F. The Dynamo: Its Theory, Design, and Manu-
facture. 190 Illustrations. 8vo, cloth. $3.00.

HEAVISIDE, 0. Electromagnetic Theory. 8vo, cloth. 2 vols. Each, $5.00.
HOBBS, W. R. P. The Arithmetic of Electrical Measurements. With numerous

examples, fully worked. Ninth Edition. 12mo, cloth. 50 cents.
HOPKINS, N. M. Experimental Electrochemistry, Theoretically and Practically

Treatsd. Profusely illustrated with 130 new drawings, diagrams, and

photographs, accompanied by a Bib'iography. 8vo, cloth. Illustrated.

284 pages. Net, $3.00.

4 LIST OF WORKS ON ELECTRICAL SCIENCE.

HOUSTON, £. J.y Prof. A Dictioiuuy of Electrical Words, Terms, and Pbrmses.

Fourth Edition, rewritten and greatly enlarged. 570 Illustiations. LAige.
8vo, cloth. $7.00.

HUTCHOrSON, It W., Jr. Long-Distance Electric Power Transmission r Being a
Treatise on the Hydro-Electric. Generation of Energy; Its Transformation,
Transmission, and Distribution. 12mo, doth, about 350 pp. Illustrated.
In Press.

INCAHBESCENT ELECTRIC LIGHTING. A Practical Description of the Edison
System, by H. Latimer. To which is added: The Design and Operation of
Incandescent Stations, by C. J. Field; A Description of the Edison Electro-
l3rte Meter, by A. E. Kennelly; and a Paper on the Maximum Efficiency of
Incandescent Lamps, by T. W. Howell. Illustrated. 16mo doth. (No.
57 Van Nostrand's Science Series.) 50 cents.

INDUCTION COILS: How Made and How Used. Third Edition. 16mo, doth.
(No. 53 Van Nostrand's Science Series.) 50 cents.

JEHL, FRANCIS, Member A.LE.E. The Manufacture of Caribous for Electric

Lighting and other purposes. Illustrated with numerous Diagrams, Tables,
and Folding Plates. Illustrated. 8vo, cloth. $4.00.

JONES, HARRT C. Outlines of Electrochemistry. 8vo, doth. Illustrated. $1.50.

KAPP, GISBERT, C. E. Electric Transmission of Energy and its Transformation,
Subdivision, and Distribution. A Practical Handbook. Fourth Edition,
thoroughly revised. 12mo, cloth. $3.50.

Alternate-Current Machinery. 190 pp. Illustrated. (No. 96 Van Nostrand's
Science Series.) 50 cents.

Dynamos, Alternators, and Transformers. Illustrated. 8vo, doth. $4.00.

KELSEY, W. R. Continuous-Current Dynamos and Motors, and their Control;
being a series of articles reprinted from the ''Practical Engineer," and com-
pleted by W. R. Kdsey, B.Sc. With Tables, Figures, and Diagrams. 8vo,
cloth. Illustrated. $2.50.

KEMPE, H. R. The Electrical Engineer's Pocket-Book: Modem Rules, Formulae,
Tables, and Data. Second Edition, with additions. 32mo, leather. $1.75.
A Handbook of Electrical Testing. Fifth Edition. 200 Illustrations. 8vo,
cloth. $6.00.

KENNEDY, R. Modem Engines and Power Generators. 4to, doth. Dlustrated.
5 vols. Each, $3.50.
Electrical Installations of Electric Light, Power, and Traction Machinery. 5 vols.
8vo, doth, niustrsted. Each, $3.50.

KENNELLT, A. E. Theoretical Elements of Electro-Dynamic Machinery. Vol. L
Illustrated. 8vo, doth. $1.50.

KILGOUR, M. H., SWAN, H., and BIGGS, C. H. W. Electrical Distribution: Its
Theory and Practice. Illustrated. 8vo, cloth. $4.00.

LIST OF WORKS ON ELECTRICAL SCIENCE. 6

LIVERMOREy V. P., and WILLIAMS, J. How to Become a Competent Motorman:
being a practical treatise on the proper method of operating a street-railway
motor-car; also giving details how to overcome certain defects. 16mo,
cloth. lUustrated. $1.00.

LOCKWOOD, T. D. Electricity, Magnetism, and Electro-Telegraphy. A Prac<
tical Guide and Handbook of General Information for Electrical Students,
Operators, and Inspectors. Fourth Edition. Illustrated. 8vo, cloth.
$2.50.

L0RIN6, A. E. A Handbook of the Electro-Magnetic Telegraph. Fourth Edition,
revised. 16mo, cloth. (No. 39 Van Nostrand's Science Series.) 50 cents.

LUPTON, A. PARR, G. D. A., and PERKIN, H. Electricity AppUed to Mimng.
With Tables, Diagrams, and Folding Plates. 8vo, cloth, 280 pp. Illustrated.
Net, $3.50.

MAILLOUX, C. 0. Electric Traction Machinery. 8vo, doth. In Press.

MANSFIELD, A. N. Electromagnets: Their Design and Construction. (Van
Nostrand's Science Series. No. 64.) 50 cents.

MAVER, WM., Jr. American Telegraphy and Encyclopedia of the Telegraph Sys-
tems, Apparatus, Operations. 450 Illustrations. Fifth Edition, revised.
8vo, cloth. $5.00.

NIPHER, FRANCIS E., A.M. Theory of Magnetic Measurements. With an
Appendix on the Method of Least Squares. 12mo, cloth. $1.00.

NOLL, AUGUSTUS. How to Wire Buildings. A Manual of the Art of Interior
Wiring. New Edition. In Press. 8vo, cloth. Illustrated.

OHM, G. S., Dr. The Galvanic Circuit Investigated Mathematically. Berlin,
1827. Translated by William Francis. With Preface and Notes by the
Editor, Thos. D. Lockwood. 12mo, cloth. (No. 102 Van Nostrand's
Science Series.) 50 cents.

OUDIN, MAURICE, A. M. S. Standard Polyphase Apparatus and Systems. Illus-
trated, with many Photo-reproductions, Diagrams, and Tables. Fourth
Edition, revised. 8vo, cloth. $3.00.

PALAZ, A. Treatise on Industrial Photometry. Specially applied to Electric
Lighting. Translated from the French by G. W. Patterson, Jr., Assistant
Professor of Physics in the University ot Michigan, and M. R. Patterson, B.A.
Second Edition. Fully Illustrated. 8vo, cloth. $4.00.

PARR, G. D. A. Electrical Engineering Measuring Instruments, for Commercial
and Laboratory Purposes. With 370 Diagrams and Engravings. 8vo, cloth.
Illustrated. Net, $3.50.

PARSHALL, H. F., and HOBART, H. M. Armature Windings of Electric Machines.
Second Edition. With 140 full-page Plates, 65 Tables, and descriptive
letter-press. 4to, cloth. $7.50.

6 LIST OF WORKS ON ELECTRICAL SCIENCE.

PERRINE, F. A. C, A.]f., D.Sc. Conductors for Electrical Distrilmtion: Their
Manufacture and Materials, the Calculation of Circuits, Pole-Line Construe-
tion, Underground Working, and other Uses. 8vo, cloth. Illustrated.
Net, $3.50.

PLANTS, GASTON. The Storage of Electrical Energy, and Researches in the
Effects created by Currents combining Quantity with High Tension. Trans-
lated from the French by Paul B. Elwell. 89 Illustrations. Svo. $4.00.

POPE, F. L. Modem Practice of the Electric Telegraph. A Handbook for Elec-
tricians and Operators. An entirely new work, revised and enlarged, and
brought up to date throughout. Illustrations. Svo, doth. $1.50.

RAPHAEL, F. C. Localization of Faults in Electric-Light Mains. Second Edition*
revised. Svo, doth. Illustrated. Net, $3.00.

RAYMOND, E. B. Alternating-Current Engineering, Practically Treated. With
many Figures and Diagrams. Second Edition, revised. Svo, doth. Illus-
trated. Net, $2.50.

SALOMONS, Sir DAVID, M.A. Electric-Light Installations. A Practical Hand-
book. Seventh Edition, revised and enlarged. Vol. I.: Management of
Accumulators. Illustrated. 12mo, cloth. Reprinting. Vol. II.: Apparatus
Illustrated. 12mo, doth. $2.25. Vol. III.: Application. Illustrated.
12mo, cloth. $1.50.

SCHELLEN, H., Dr. Magneto-Electric and Dynamo-Electric Machines. Their
Construction and Practical Application to Electric Lighting and the Trans-
mission of Power. Translated from the Third German Edition by N. S.
Keith and Percy Ne3anann, Ph.D. With very large Additions and Notes
relating to American Machines, by N. S. Keith. Vol. I. With 353 Illus-
trations. Third Edition. $5.00.

SEVER, G. F. Electrical Engineering Experiments and Tests on Direct-Current
Machinery. With Diagrams and Figures. Svo, pamphlet. Illustrated.
Net, $1.00.

SEVER, G. F., and TOWNSEND, F. Laboratory and Factory Tests in Electrical
Engineering. Svo, cloth. Illustrated. 225 pp. Net, $2.50.

SEWALL, C. H. Wireless Telegraphy. With Diagrams and Figures. Second
Edition, corrected. Svo, cloth. Illustrated. Net, $2.00.
Lessons in Telegraphy. 12mo, cloth. Illustrated. Net, $1.()0. In Press.

SEWELL, T. Elements of Electrical Engineering. Second Edition, revised.
Svo, cloth. Illustrated. 432 pp. Net. $3.00.

SHELDON, S., Ph.D., and MASON, H., B.S. Dynamo-Electric Machinery; Its
Construction, Design, and Operation. Direct-Current Machines. Fifth
Edition, revised. Illustrated. Svx), cloth. Net, $2.50.
Alternating-Current Machines: being the second volume of the author's ^'Dy-
namo-Electric Machinery: its Construction, Design, and Operation." With
many Diagrams and Figures. (Binding imiform with Volume I.) Fourth
Edition. Illustrated. Svo, cloth. Net, $2.50.

LIST OP WORKS OK ELECTRICAL SCIENCE. 7

SLOAlfE, T. O'CONOR, Prof. Standard Blectrical Dictionary. 300 Illustrations.
8vo, cloth. $3.00.

SNELL, ALBION T. Electric Motive Power. The Transmission and Distribution
of Electric Power by Continuous and Alternating Currents. With a Section
on the Applications of Electricity to Mining Work. Illustrated. 8vo, cloth.
$4.00.

SODDT, F. Radio-actlTity: an Elementary Treatise from the Standpoint of the
Disintegration Theory. Fully Illustrated, and with a complete table of
Contents and Extended Index. 8vo, doth. Illustrated. Net, $3.00.

SWINBURNE, JAS., and WORDINGHAM, C. H. The Measurement of Electric
Currents. Electrical Measuring Instruments. Meters for Electrical Eneigy.
Edited, with Preface, by T. Commerford Martin. Folding Plate and nmner-
ous Illustrations. 16mo, cloth. 50 cents.

SWOOPE, C. WALTON. Practical Lessons in Electricity: Principles, Experi-
ments, and Arithmetical Problems. An Elementary Text-book. With
numerous Tables, Formulae, and two large Instruction Plates. Sixth Edi-
tion. Illustrated. Svo, cloth. Net, $2.00.

THOM, C, and JONES, W. H. Telegraphic Connections, embracing recent methods
in Quadruplex Telegraphy. 20 Colored Plates. Svo, doth. $1.50.

THOMPSON, S. P., Prof. Dynamo-Electric Machinery. With an Introduction
and Notes by Frank L. Pope and H. R. Butler. Fully Illustrated. (No. 66
Van Nostrand's Science Series.) 50 cents.

Recent Progress in Dynamo-Electric Machines. Being a Supplement to
"Dynamo-Electric Machinery." Illustrated. 12mo, cloth. (No. 76 Van
Nostrand's Science Series.) 50 cents.

Dynamo-Electric Machinery. Vol. I. Svo, cloth, 996 pp. 573 Illustrations.
4 Colored and 32 Folding Plates. $7.50.

TREVERT, E. How to BiiUd Dynamo-Electric Machinery. Embracing the
Theory, Designing, and Construction of Dynamos and Motors. With
Appendices on Fidd-Magnet and Armature Winding, Management of
Djmamos and Motors, and useful Tables of Wire Gauges. Illustrated.
Svo, cloth. $2.50.

TUNZELMANN, G. W. de. Electricity in Modem Life. Illustrated. 12mo, doth.
$1.25.

UNDERHILL, C. R. The Electromagnet: Being a new and revised edition of
"The Electromagnet," by Townsend Walcott, A. E. Kenndly, and Richard
Varley. With Tables and Numerous Figures and Diagrams. 12mo, cloth.
lUustrated. $1.50.

8 LIST OF WORKS ON ELECTRICAL SCIENCE.

URQUHART, J. W. Dynamo Construction. A Practical Handbook for the use
of Engineer Constructors and Electricians in Charge. Illustrated. 12mo,
doth. $3.00.

Electric Ship-Lighting. A Handbook on the Practical Fitting and Running of
Ship's Electrical Plant, for the use of Ship Owners and Builders, Marine
Electricians, and Sea-going Engineers in Charge. 88 Illustrations. 12mo,
cloth. $3.00.

Electric-Light Fitting. A Handbook for Working Electrical Engineers, em-
bodying Practical Notes on Installation Management. Second Edition, with
additional chapters. With numerous Illustrations. 12mo, cloth. $2.00.

Electroplating. Fourth Edition. 12mo, doth. $2.00.

Elcctrotyping. 12mo, doth. $2.00.
WADE, E. J. Secondary Batteries: Their Theory, Construction, and Use. With
innumerable Diagrams and Figures. 8vo, doth. Illustrated. Net, $4.00.

WALKER, FREDERICK. Practical Dynamo-Building for Amateurs. How to
Wind for any Output. Illustrated. 16mo, cloth. (No. 98 Van Nostrand's
Science Series.) 50 cents.

WALLING, B. T., Lieut-Corn. n.S.N., and MARTIN, JULIUS. Electrical Installa-
tions of the United States Navy. With many Diagrams and Engravings.
In press.

WATT. Electroplating and Refining of Metals. 8vo, doth. Illustrated. Net,
$4.50.
Electro-Metallurgy. Eleventh Edition. 12mo, cloth. $1.00.

WEBB, H. L. A Practical Guide to the Testing of Insulated Wires and Cables.

niustrated. 12mo, cloth. $1.00.

WEEKS, R. W. The Design of Alternate-Current Transformer. New Edition.
In press.

WEYMOUTH, F. MARTEN. Drum Armatures and Commutators. (Theory and
Practice.) A complete treatise on the theory and construction of drum-
winding, and of commutators for closed-coil armatures, together with a full
r6sum^ of some of the principal points involved in their design; and an
exposition of armature reactions and sparking. Illustrated. 8vo, doth.
$3.00.

WILKINSON, H. D. Submarine Cable-Laying, Repairing, and Testing. 8vo,
doth. Reprinting.

I yG522

JV-^Jk-wxA;*^