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$8 57b 725

RADIODYNAMICS

THE WIRELESS CONTROL OF TORPEDOES
AND OTHER MECHANISMS

B. F. MIESSNER

Associate Member Institute of Radio Engineers,
Expert Radio Aide, U, S. Navy

112 ILLUSTRATIONS

NEW YORK

D. VAN NOSTRAND COMPANY

25 Park Place

1916

D. VAN NOSTRAND COMPANY

Stanbope |hre90

H. GILSON COMPANY
BOSTON, U.S A.

PREFACE

In the preparation of this work the author has endeavored
to present in an orderly and instructive fashion the most
important material concerning the history, methods and
apparatus of Radiodynamics, the art of controlling distant
mechanisms without artificial connecting means.

He has aimed especially at a treatment of his subject-matter
that would be intelligible to the general reader without sacri-
ficing the technical exactitude which makes scientific work of
value to the trained engineer.

The chief recent developments in this new art have been
of a military nature, and for this reason the volume is devoted
for the most part to the torpedo-control applications of
Radiodjoiamics.

It is hoped that the book may prove interesting to the gen-
eral scientific reader, as well as to the trained engineer, and
to those concerned in the purely military applications and
possibilities of wirelessly-controUed mechanisms.

The author desires here to thank the many friends who
have generously assisted him in collecting his materials. He
desires especially to express his obligation to Professor M. H.
Liddell, of Purdue University for his advice and assistance in
the preparation of the book for press.

B. F. M.

Lafayette, Ind.,
August, 1916.

389478

CONTENTS

CHAPTER PAGE

I. Historical i

i^-^ IT. Wireless Control of Mechanisms 6

ni. Practical Wireless Telegraphy 12

rv. Electrostatic and Combined Induction — Conduction Tele-
graph Systems 19

V. Electromagnetic Wave Systems 27

VI. Possible Control Methods for Radiodynamics — Sound

Waves 33

Vr[. Infra-red or Heat Waves 41

VIII. Visible and Ultra-violet Waves 57

IX. Earth Conduction 67

X. Electrostatic and Electromagnetic Induction — Hertzian

Waves 74

XI. The Advent of Wirelessly Controlled Torpedoes 78

XII. Selectors 89

XIII. European Control Systems •. 92

XIV. Work of the Hammond Radio Research Laboratory 107

XV. The Solution of the Problems Related to Battle-range

Torpedo Control 124

XVI. The Difficulties Encountered in Providing Protection

from Interference 137

XVII. A Means of Obtaining Selectivity 145

XVIII. Nature of Indicator Currents in Radio Receivers 150

XIX. The Interference Preventer 159

XX. Detectors 167

XXI. Methods of Increasing Received Effects 175

XXII. Relays 180

XXIII. Torpedo Antennae 183

XXIV. Recent Developments 188

RADIODYNAMICS

CHAPTER I
fflSTORICAL

From earliest times methods of conveying intelligence to a
distance have been universally known and utilized. Fleet-
footed runners, fires and torches by night, and smoke by day
as well as acoustic methods using both air and earth as con-
ducting mediums seem to have been among the first means of
comparatively distant signalling. We read of them in the
Bible (Jeremiah) and in the Greek and Latin authors; their
use in the far East and in Europe leaves no doubt as to their
wide employment amongst civilized nations.

The Indians of America from the North to Cape Horn still
use lighted fires and blanket-controlled sfnoke clouds to an-
noimce special tidings and convey important messages; their
system of optical signalling in which the arms were used,
furnished the basis for the semaphore, which toward the end
of the eighteenth century came into general use in Europe.
It may still be seen on any railroad. The semaphore system
was still further elaborated for maritime and military pur-
poses and today in the armies and navies of the world we
have semaphore and flag signalling as a very important means
of communicating intelligence to distances not in excess of a
few miles. The heliograph by day and the electric search-
light by day and night can both trace their evolution to the
primeval fire and torch.

:'A ': f/f : : ', */< ; • :}^ RAplODYNAMlCS

The application of electricity has revolutionized all pre-
vious methods of signalling. The phenomenon of attraction
was well known to the ancients. Thales, the founder of
Ionic philosophy, who lived six hundred years before Christ,
noticed the effects of friction on amber, and Theophrastus,
Pliny and other writers recorded similar phenomena.

In 1727 Stephen Gray, a pensioner of the Charter House,
London, made an electric discharge pass over a circuit of
700 feet. Shortly after the discovery of the Leyden jar by
Muschenbroek of Leyden, in 1746, Dr. Watson, a bishop of
Llandaff, transmitted a charge through 2800 feet of wire.
In the same year he increased the distance of transmission to
10,600 feet through wires stretched on poles erected on
Shooter's Hill, London. Benjamin Franklin made similar ex-
periments in 1748 over the Schuylkill river at Philadelphia.
Le Sage of Geneva established the first telegraph system for
the transmission of intelligible signals in 1774*; this system
was based on electrostatic action. The next important law
was discovered by Romagnesi of Trente in 1805; but at-
tracted little attention imtil it was rediscovered in 18 19 by
Oersted. This discovery showed that a current-carrying wire
is able to deflect a magnetic needle. Schweigger in 1820
discovered that the deflecting force was increased by wmding
the wire several times around the needle. These very im-
portant discoveries paved the way for the galvanoscope and
galvanometer. Galvanoscopic or needle telegraphs were sub-
sequently evolved.

In 1832 Schilling, a Russian, devised a single-needle tele-
graph using reverse currents and combinations of signals for
an alphabet. Schilling's telegraph was developed by Gauss
and Weber, who built a line three miles long at Gottingen.

While Prof. A. C. Steinheil of Munich was establishing a
system of telegraphy in Bavaria, Gauss, the celebrated German
* Moigno*s " T616graphie Electrique," p. 59.

HISTORICAL 3

philosopher and himself a telegraph inventor, suggested to
him that the two rails of a railway might be used as telegraph
conductors. In July, 1838, Steinheil tried the experiment on
the Nurmberg-Furth railway, but was imable to obtain an
insulation of the rails sufficiently good for the current to
reach from one station to the other. The great conductiv-
ity with which he found that the earth was endowed led
him to presume that it would be possible to employ it instead
of the return wire or wires hitherto used. The trials that he
made in order to prove the accuracy of this conclusion were
followed by complete success, and he then introduced into
electric telegraphy one of its greatest improvements — the
earth return circuit.^*

Following Sturgeon's invention of the electromagnet in
1825 and the simultaneous discovery by Faraday in England
and Henry in America (1831) of the laws of electromagnetic
induction, Morse laid the foundations in 1836 of the present
overland electromagnetic telegraph system. In the same
year in England Wheatstone with W. F. Cooke still further
perfected the needle telegraph and a year later put a crude
system of telegraphy into actual service on the London and
Blackwell Railway. In 1839 the first public line was opened
by Wheatstone between Paddington and Slough, England,
twenty miles of goose quills being used for insulation.

It was once supposed that Wheatstone was the original
inventor of the electric telegraph, but strictly speaking it had
no inventor; it is rather the result of accumulated discoveries
each adding its quota to advance the invention towards per-
fection. The greatest achievement of Wheatstone was his
automatic, recording telegraph, which is extensively used for
press and other long dispatches and which has attained
marvelous speeds for a mechanical recorder.

* For an account of the earth return before 1838 see Fahie*s "History of
Electric Telegraphy to the Year 1837," pp. 343-348.

4 RADIODYNAMICS

Morse constructed his electromagnetic telegraph in 1836,
and in the next few years he devised many important modi-
fications. Congress made him an appropriation of $30,000 in
March, 1843, ^^^ on the 24th of March, 1844, the first tele-
graph line in the United States was successfully opened between
Washington and Baltiniore, a distance of about 40 miles.

The electrostatic telegraph of Le Sage was probably the
first instance of the control of mechanisms from a distance
by the use of conducting wires. The real art of teledy-
namics,* however, is based on the discoveries, by Romagnesi,
Oersted, and Schweigger of the phenomena of electromagnet-
ism which led up to the conception and development of the
electromagnetic telegraph. Since 1836, when Morse con-
structed his first telegraph, no very radical changes have been
made in the general scheme on which his system was based,
but it has been gradually and surely developed and brought to
the present stage of perfection. One very conspicuous change
in detail, however, is worthy of mention. The electromagnetic
sounder first used by Morse on the line between Washington
and Baltimore and exhibited in the National Museum in
Washington weighed one hundred eighty-five poimds. The
arms were three and one-half inches in diameter and eighteen
inches long, the same size of copper wire being used for the
coils as for the line wire. It was then supposed > that the
wire of the coils and of the line should be of the same size
throughout, and even down to i860 many practical telegraph-
ers held this view.f The sounders now used weigh about
one pound and require no more than about seventy-five
cubic inches of space. The coils are wound with wire much
smaller than the line wire, a great increase in sensitiveness
being thereby produced.

* The art of controlling mechanisms from a distance; as used here it refers
only to distant control, by electrical means, with or without connecting wires.
t London Electrical Review, Aug. 9, 1895, p. 157.

HISTORICAL 5

The necessity for long-distance telegraphy brought about
the invention of the relay, a very sensitive form of sounder
which is actuated by the weak line currents and which in
turn controls the current for operating the sounder used in
receiving messages. The relay is a very important part of
all systems for the distant control of mechanisms as by its
use practically any amount of power can be controlled. The
mere pressure of the finger on a telegraph key through which
a few thousandths of an ampere flow to a distant relay is
sufiicient to start or stop the most powerful machinery or to
set off explosive charges strong enough to destroy a whole
city.

Such mechanisms as electric bells and signals of various
kinds, telephone and fire alarm systems, electric clocks and
chimes, and time distribution systems are all developments
in the art of teledynamics. Present-day automatic tele-
phone systems, the distant control of searchlights, and the
wire-controlled torpedo are examples of the wonderful possi-
bilities along these lines.

CHAPTER II
WIRELESS CONTROL OF MECHANISMS

Like most wonderful inventions the telegraphic transmission
of signals without the aid of conducting wires is in reality
not an invention, according to the popular conception of the
word, but rather the result of the combined efforts of many
deep-thinking scientific men extending over a period of many
years. After the discovery of the galvanic current and elec-
tromagnetism in the seventeenth and eighteenth centuries
the conception and development of wireless telegraphy and
wire telegraphy occurred at practically the same time. It
was in 1836 that Morse constructed his first telegraph; this
was not put into practical operation until 1844. In 1838
Steinheil of Munich, one of the great pioneers of electric
telegraphy in Europe, gave the first intelligent* suggestion
of a wireless telegraph. In a paper on this subject Steinheil,
explaining his theories and observations on earth conduction
telegraphy, says:

''The inquiry into the laws of dispersion according to which
the ground, whose mass is imlimited, is acted upon by the
passage of a galvanic current appeared to be a subject replete
with interest. The galvanic excitation cannot be confined

* Earlier but vague and impractical suggestions were made previous to this
time. In the Bible we find: " Canst thou send lightnings, that they may go,
and say unto thee, * Here we are ? ' "

In 1632 Galileo wrote of a secret art by which it would be possible to con-
verse across a space of several thousand miles through the attraction of a
magnetic needle (" Galilei Systema Cosmicum." Dial. I). The "Prolusiones
Academicae" of Strada, which was published in 161 7, described a method of
communicating at a distance by means of two pivoted magnetic needles.

WIRELESS CONTROL OF MECHANISMS 7

to the portions of earth situated between the two ends of the
wire; on the contrary it cannot but extend itself indefinitely
and it therefore only depends on the law that obtains in this
excitation of the ground, and the distance of the exciting ter-
minations of the wire, whether it is necessary or not to have
any metallic commimication at all for carrying on telegraphic
intercourse.

"An apparatus can it is true be constructed in which the
inductor, having no other metallic connection with the
multiplier than the excitation transmitted through the ground,
shall produce galvanic currents in that multiplier sufficient
to cause a visible deflection of the bar. This is a hitherto
unobserved fact and may be classed amongst the most ex-
traordinary phenomena that science has revealed to us. It
only holds good, however, for small distances; and it must be
left to the future to decide whether we shall ever succeed in
telegraphing at great distances without any metallic con-
nection at all. My experiments prove that such a thing is
possible up to distances of fifty feet. For greater distances
we can only conceive it feasible by augmenting the power of
the galvanic induction, or by appropriate multipliers con-
structed for the purpose, or, in conclusion, by increasing the
surface of contact presented by the ends of the multipliers.
At all events the phenomenon merits our best attention, and
its influence will not perhaps be altogether overlooked in the
theoretic views we may form with regard to galvanism
itself."*

Discussing the same subject in another publication Stein-
heil says: "We cannot conjure up gnomes at will to convey
our thoughts through the earth. Nature has prevented this.
The spreading of the galvanic effect is proportional not to
the distance of the point of excitation but to the square of
this distance; so that at the distance of fifty feet only ex-
♦ Sturgeon's "Annals of Electricity," vol. iii, p. 450.

8 RADIODYNAMICS

ceedingly small effects can be produced by the most powerful
electrical effect at the point of excitation. Had we means
which could stand in the same relation to electricity as the
eye stands to light nothing would prevent our telegraphing
through the earth without conducting wires; but it is not
probable that we shall ever attain this end." *

Steinheil apparently received his inspiration for this method
of transmitting signals iFrom his accidental discovery of the
conductivity of the earth in the experiments on the Nurm-
berg-Furth railroad. His explanation, which is somewhat
nebulous and obscured by such expressions as "multipliers,"

\F/afes^ ^^^ ^^^ ^P/ote'

Fig. I.

"galvanic excitation," and "galvanic induction," actually
amoimts to this: When two earthed conducting plates are
connected to an electric battery, current flows through the
earth, but not wholly through that portion directly between
the plates. Instead, the current obeys Ohm's law with re-
gard to a circuit including conductors in parallel, i.e., the
current in any branch is inversely proportional to its resist-
ance. The number of parallel branches in the earth circuit
is infinite, but they obey this same law. The earth between
the buried plates, although having a high specific resistance,
has a very great cross sectional area; this accounts for the
relatively low resistance of earth returns. The current

* The electric eye of Hertz! "Die Anwendung des Electromagnetismus,"
i873» P- 172.

WIRELESS CONTROL OF MECHANISMS g

density, according to Ohm's law is greatest between the
plates, and decreases in proportion to the distance along any
line at right angles to the line joining the plates. This is
shown in Fig. i.

Steinheil's scheme was to so place another set of earth plates
connected by a wire and current indicator that the current
would traverse the earth between
the sending and receiving plates,
as shown in Fig. 2, and thus
operate the receiving instrument.

SteinheiPs inability to signal
over distances greater than fifty

feet was, no doubt, due to the ' ^eceTX^ indicator

limited capacity of his current fig 2

supply, the insensitiveness of his

receiving indicator, and his probable ignorance of the fact that
the distance between the transmitting plates should be at least
three times the distance to be bridged, for the best results.

Another means of signalling without connecting wires was
disclosed by Steinheil in a classic paper on '* Telegraphic
Commimication, especially by means of Galvanism.*' This
method is particularly interesting because of its similarity
to the Photophone, invented by Alexander Graham Bell and
Simmer Tainter a half century later. Describing his idea
Steinheil says in part: "Another possible method of bringing
about transient movements at great distances, without any
intervening conductor, is furnished by radiant heat, when
directed by means of condensing mirrors upon a thermo-
electric pile.* A galvanic current is called into play, which in
its turn is employed to produce declinations of a magnetic
needle. The difficulties attending the construction of such

* In recent years thenno-pfles have been developed to such an extent that
the heat radiated by stars can be detected and measured. W. W. Coblentz, of
the U. S. Bureau of Standards, has described, in various publications issued by

lO RADIODYNAMICS

an instrument, although certainly considerable, are not in
themselves insuperable. Such a telegraph however would
only have this advantage over those semaphores based on
optical principles — namely, that it does not require the con-
stant attention of the observer; but, like the optical one, it
would cease to act during cloudy weather, and hence partakes
of the intrinsic defects of all semaphoric methods." *

It is not probable that Steinheil ever worked this idea into
usable form, as no accounts of experunents can be found,
but to him is the credit really due for first (1839) suggesting
a means of signalling without conducting wires by the use of
radiant energy, and his was in all probability the first radio-
telegraphic system disclosed to the world.

Another way of conveying intelligence in a manner closely
related to those already given depends upon the sonorescent
property of substances. The voice-controlled transmitting
beam of light or heat is allowed to fall upon suitable material,
such, for instance, as a sheet of hard rubber. The periodic
expansion and contraction of this material, caused by the
periodic variations in the intensity of the heat imparted by
the beam, cause the rubber disc to reproduce the sounds made
near the transmitter.

Davy's Sound-relajring System

Edward Davy, in 1838, proposed a system of wireless
signalling, which, though not of any practical value, is worthy
of mention because the principle involved very closely re-

that institution, micro-radiometers which are sufliciently sensitive to detect the
heat of a standard candle at fifty-three nules. Edison's *' tasimeter," which
he devised for studying the streamers of the sun during an eclipse, is reported
to have been so sensitive that a person at a distance of thirty feet could produce
a perceptible effect merely by turning his face toward the instrument. The
Crookes radiometer, the Duddell thermo-galvanometer, and the bolometer
bridge may also be used as detectors of radiant heat.
* Sturgeon's "Annals of Electricity," Mar., 1839.

WIRELESS CONTROL OF MECHANISMS II

sembles our modern schemes of relaying, which are applied
in long-distance telegraphy and kindred branches of the art.
The energy is transmitted a short distance to a receiver
which responds, controls a local source of energy, and sends
the signal on in duplicate to the next station, this operation
being repeated a sufficient number of times to bridge the re-
quired distance. Davy, however, had in mind the conjoint
use of sound and electricity for accomplishing this end. His
plan was as follows: Stations placed about a mile apart should
be fitted with powerful means of producing sound waves to-
gether with suitable means, such as our common megaphones,
for directing them to the receiver and concentrating them
upon some delicate form of vibratory relay. This relay
would vibrate in resonance with the transmitted sound
waves, close the circuit for energizing a local means of sound
production similar to the first, and thus relay the signals on
to the next station. Obviously, such a system was impractical
in comparison with other ideas advanced at that time,
principally because of the numerous stations necessary to
bridge a relatively short distance, and the power required
at each of these to produce sound waves of sufficient ampli-
tude to operate the vibratory relay a mile away. John
Gardner of England has developed sensitive vibratory relays
with which he can control lights, motors, bells, etc., across
a large room by whistling the tone corresponding in fre-
quency to the natural period of the vibratory diaphragm or
reed.*

* For other references to this subject, see Signor Senliq d* Andres, Tele-
graphic Journal, vol. ix, p. 126; A. R. Sennet, Joum. Inst. Elec. Eng., No. 137, p.
908. See also U. S. Hydrographic Office Bulletin of May 13, 1914 on the " Fes-
senden Oscillator for the Detection of Icebergs," Professor Dayton C. Miller's
work with his " Phonodik," described in his book on " The Sdence of Musical
Sounds " (Macmillan Co.), Tests on Fessenden Submarine Signalling Apparatus,
Journal U. S. Art. War, Apr. 1915; see also Sci. Am., July 4, 1914 — and the
American Magazine, April, 191 5.

CHAPTER in
PRACTICAL WIRELESS TELEGRAPHY

The first experiments of importance with the new earth
conduction telegraphy appear to have been made by Professor
Morse, who, in 1842, actually transmitted signals a distance
of nearly a mile across the Susquehanna river *

In a letter to the Secretary of the Treasury which was sub-
sequently laid before the House of Representatives, Morse
says: . *

'*In the autumn of 1842, at the request of the American
Institute, I undertook to give to the public in New York a
demonstration of my telegraph, by connecting Governor's
Island with Castle Garden, a distance of a mile; and for this
purpose I laid my wires properly insulated beneath the
water. I had scarcely b^gun to operate, and had received
but two or three characters when my intentions were frus-
trated by the accidental destruction of a part of my con-
ductors by a vessel, which drew them up on her anchor, and
cut them off. In the moments of mortification I immedi-
ately devised a plan for avoiding such an accident in the
future, by so arranging the wires along the banks of the river
as to cause the water itself to conduct the electricity across.
The experiment, however, was deferred imtil I arrived in
Washington; and on Dec. 16, 1842, I tested my arrangement
across the canal and with success. The simple fact was
then ascertained that electricity could be made to cross a
river without other conductors than the river itself; but it
was not until the last autumn that I had the leisure to make

* From this we learn that Morse actually operated a wireless telegraph
before his Washington-Baltimore wire system was opened for service.

PRACTICAL WIRELESS TELEGRAPHY 13

a series of experiments to ascertain the law of its passage.
The following diagram (Fig. 3) will serve to explain the
experiment:

** A, B, C, D are the banks of the river; N, P is the battery;
G is the galvanometer; ww are the wires along the banks
connected with copper plates, f, g, h, i, which are placed in
the water. When this arrangement is complete, the elec-
tricity, generated by the battery, passes from the positive
pole P to the plate h, across the river through the water to

t \

Y/
Fig. 3.

plate i, and thence around the coil of the galvanometer to
plate f, across the river again to plate g, and thence to the
other pole of the battery. The distance across the canal is
eighty feet; on August 24 the following were the results of
the experiment* . . . showing that electricity crosses the
river and in quantity in proportion to the size of the plates
in the water. The distance of the plates on the same side of
the river from each other also affect the result. Having
ascertained the general fact I was desirous of discovering the
best practical distance at which to place my copper plates,
and not having the leisure myself, I requested my friend,
Professor Gale, to make the experiments for me." . . .

The experiments made by Professor Gale indicate that the
distance between the plates along the shores should be approxi-
mately three times greater than that from shore to shore

* The table containing information only of general interest is omitted.

14 RADIODYNAMICS

across the stream, since four times the distance did not give
any increase in power and less than three times the distance
diminished the deflections of the galvanometer considerably.
Between 1854 and i860 James Bowman Lindsay made similar
attempts at wireless telegraphy by utilizing water as the
conducting medium.

With an apparatus like that of Morse, Lindsay finally suc-
ceeded in signalling across the river Tay, where it is more
than a mile wide.*

J. W. Wilkins of the Cooke and Wheatstone Telegraph Co.
also experimented with earth conduction telegraphy in 1845,
and published the results of his investigations in the Mining
Journal, March 31, 1849, under the heading '* Telegraph
Communication between England and France." t

Invention of the Telephone

After the invention of the telephone, in 1876, wireless
telegraphy went forward with leaps and bounds. The
marvelous sensitiveness of this instrument, which will give
audible responses under the application of less than one-
millionth of a volt of electromotive force, is largely responsible
for the great progress made along these lines. Even wireless
telephony was introduced.

Its use in a telegraph line running parallel to another line
through which telephone conversation and singing was being
carried, led to the accidental discovery of its extraordinary
sensitiveness to induction currents in 1877, by Mr. Charles
Rathbone of Albany, N. Y.t

* See "Electrical Engineer," vol. xxiii, pp. 21-51; Kerr, "Wireless Teleg-
raphy," 1898, p. 40.

t For detailed accounts of his work see Fahie's "History of Wireless
Telegraphy," pp. 32-38.

t Journal of the Telegraph, Oct. i and 16; and Nov. i, 1877. For simi-
lar observations see Telegraphic Journal, Mar. i, 1788, p. 96; Journal of the
Telegraph, Mar. 16, 1878, Dec. i, 1877; The Electrician, vol. vi, pp. 207-303.

PRACTICAL WIRELESS TELEGRAPHY 1$

These observations on inductive eflfects in telephone cir-
cuits began to be investigated; in 1877 Prof. E. Sacher of
Vienna found that signals from three Smee cells sent through
one wire 120 m. long could be distinctly heard in the telephone
in another and parallel wire 20 m. distant.*

Prof. John Trowbridge of Harvard University was the first
to systematically study the problem of electromagnetic in-
duction signalling. His attention is concentrated chiefly on
the use of interrupted or alternating currents at the trans-
mitter and a telephonic receiver; in other respects his circuit
was practically the same as Morse's (Fig. 3).t

In 1884 Trowbridge described another plan using a com-
bination of both electromagnetic induction and earth con-
duction; later he discussed the phenomena of induction,
electromagnetic and electrostatic, as distinguished from leak-
age or earth currents, and with reference to their employment
in wireless telegraphy. |

Experiments of Alexander Graham Bell

About 1882 Alexander Graham Bell made some successful
experiments along this line suggested by Trowbridge. In his
paper read before The American Association for the Ad-
vancement of Science, in 1884, he says:

"A few years ago I made a communication on the use of
the telephone in tracing equipotential lines and surfaces. I
will briefly give the chief points of my experiment, which was
based on experiments made by Professor Adams of King's
College, London. Professor Adams used a galvanometer in-
stead of a telephone.

"In a vessel of water I placed a sheet of paper. At two

* Electrician, vol. i, p. 194.

t His investigations are discussed in detail in "The Earth as a Conductor
of Electricity," Am. Acad. Arts and Sc, 1880; see also "Silliman's Am. Joum.
Sc, 1880.

t Sc. Am. Supp., Feb. 21, 1891.

l6 RADIODYNAMICS

points on that paper were fastened two ordinary sewing
needles, which were also connected with an interrupter that
interrupted the circuit about one hundred times a second.

*^Then I had two needles connected with a telephone; one
needle I fastened on the paper in the water, and the moment
I placed the other needle in the water I heard a musical soimd
in the telephone. By moving this needle around in the
water, I would strike a place where there would be no soimd
heard. This would be where the electric tension was the
same as in the needle; and by experimenting in the water
you could trace out with perfect ease an equipotential line
around one of the poles in the water.

**It struck me afterwards that this method, which is true
on the small, is also true on the large scale, and that it might
afford a solution of a method of communicating electric signals
between vessels at sea.

**I made some preliminary experiments in England, and
succeeded in sending signals across the river Thames in this
way. On one side were two metal plates placed at a distance
from each other, and on the other two terminals connected
with the telephone. A current was established in the tele-
phone each time a current was established through the
galvanic circuit on the opposite side, and if that current was
rapidly interrupted you would get a musical tone.

''Urged by Professor Trowbridge, I made some experiments
which are of very great value and suggestiveness. The first
was made on the Potomac river. I had two boats. In one
boat we had a Leclanche battery of six elements, and an in-
terrupter for interrupting the current very rapidly. Over the
bow of the boat we made water connection by a metallic plate,
and behind the boat we trailed an insulated wire, with a
float at the end carrying a metallic plate, so as to bring these
two elements about one hundred feet apart. I then took
another boat and sailed oflF. In this boat we had the same

PRACTICAL WIRELESS TELEGRAPHY 17

arrangement, but with a telephone in the circuit. In the
first boat, which was moored, I kept a man making signals;
and when my boat was near his I would hear those signals
very well — a musical tone, something of this kind: tum,
timi, tum. I then rowed my boat down the river, and at a
distance of a mile and a quarter, which was the farthest I
tried, I could still (distinguish those signals.

"It is therefore perfectly practicable fof steam vessels with
dynamo machines to know of one another's presence in a fog
when they come, say, within a couple of miles of one another,
or, perhaps at a still greater distance. I tried the experiment
a short time ago in salt water of about twenty fathoms in
depth; I used then two sailing boats, and did not get so
great a distance as on the Potomac. The distance, which we
estimated by the eye, seemed to be about half a mile; but
on the Potomac we took the distance accurately on the shore."

In 1886, convinced of the practicability of his method, BeU
says further:

"Most of the passenger steamships have dynamo engines
and are electrically lighted. Suppose, for instance, one of
them should trail a wire a mile long, or any length, which is
connected with the dynamo engine and electrically charged.
The wire would practically have a groimd connection by
trailing in the water. Suppose you attach a telephone to
the end on board. Then your dynamo or telephone end
would be positive, and the other end of the wire trailing be-
hind would be negative. All of the water about the ship
will be positive within a circle whose radius is one-half the
length of the wire. All of the water about the trailing end
will be negative within a circle whose radius is the other half
of the wire. If your wire is one mile long there is then a
large area of water about the ship which is affected either
positively or negatively by the dynamo engine and -the
electrically charged wire. It will be impossible for any ship

l8 RADIODYNAMICS

or object to approach within the water so charged in relation
to your ship without your telephone telling the whole story
to the listening ear. Now if a ship coming in this area has a
similar apparatus, the two vessels can conmiunicate with
each other by their telephones. If they are enveloped in
fog, they can keep out of each other's way. The ship having
the telephone can detect other ships in its track, and keep
out of the way in a fog or storm. The matter is so simple
that I hope our ocean steamships will experiment with it."*
This method of signalling, attempted later by Messrs.
Rathenau, Rubens, and Strecker, was finally carried to a
distance of nearly nine miles, but the advent of the work of
Maxwell and Hertz followed by the practical application of
their theories and discoveries by Marconi and others, proved
such an advance in method, and the futility of trying to
make earth conduction systems duplicate the records of the
new Hertzian-wave telegraphy was so evident that work along
that line was practically discontinued.

* Public Opinion, Jan. 31, 1886.

CHAPTER IV

ELECTROSTATIC AND COMBINED INDUCTION-
CONDUCTION TELEGRAPH SYSTEMS

Professor Dolbear's Electrostatic Telegraph

In 1882, at about the same time as A. G. Bell, Professor
Dolbear of Tufts College, Boston, was also engaged on the
problem of wireless telegraphy. His apparatus was some-
what more suggestive than any hitherto proposed and was
awarded a United States patent in March, 1882. The fol-
lowing is an extract from his patent specification:

IH. . B--ilh|||l|h

Fig. 4-

''In the diagram (Fig. 4), A represents one place and B
a distant place. C is a wire leading into the ground at A,
and D a wire leading into the ground at B ; G is an induction
coil having in the primary circuit a microphone transmit-
ter, T, and a battery, F, which has a number of cells suf-
ficient to establish in the wire C, which is connected with one
terminal of the secondary coil, an electromotive force of, say,

20 RADIODYNAMICS

loo volts. The battery is so connected that it not only
furnishes the current for the primary circuit, but also charges
or electrifies the secondary coil and its terminals C, and Hi.

"Now if words be spoken in proximity to transmitter T,
the vibration of its diaphragm will disturb the electrical con-
dition of the coil G, and thereby vary the potential of the
ground at B, and the receiver will reproduce the words spoken
in proximity to the transmitter, as if the wires CD were in
contact, or connected by a third wire.

"There are various well-known ways of electrifying the
wire C to a positive potential far in excess of loo volts, and
the wire D to a negative potential far in excess of loo volts.

"In the diagram, H, Hi, H2 represent condensers, the con-
denser Hi being properly charged to give the desired effect.
The condensers H and H2 are not essential, but are of some
benefit; nor is the condenser Hi essential when the secondary
coil is otherwise charged. I prefer to charge all these con-
densers, as it is of prime importance to keep the grounds of
wires C and D oppositely electrified, and while, as is obvious,
this may be done by either the batteries or the condensers, I
prefer to use both."

In the Scientific American Supplement, Dec. 11, 1886,
Professor Dolbear gives some additional particulars:

"My first results were obtained with a large magneto
electric machine with one terminal grounded through a Morse
key, the other terminal out in free air and only a foot or two
long; the receiver having one terminal grounded, the other
held in the hand while the body was insulated, the distance
between grounds being about sixty feet. Afterward much
louder and better effects were obtained by using ah induction
coil having an automatic break and with a Morse key in the
primary circuit, one terminal of the secondary grounded the
other free in air, or in a condenser of considerable capacity,
the latter having an air discharge of fine points at its opposite

TELEGRAPH SYSTEMS 21

terminal. At times I have employed a gilt kite carrying a
fine wire from the secondary coil. The discharges then are
apparently nearly as strong as if there was an ordinary
circuit.

"The idea is to cause a series of electrical discharges into
the earth without discharging into the earth the other termi-
nal of the battery or induction coil — a feat which I have been
told so many many times was impossible, but which certainly
can be done. An induction coil isn't amenable to Ohm's
law always! Suppose at one place there be apparatus for
discharging the positive pole of the induction coil into the
ground, say, loo times a second, then the ground will be
raised to a certain potential loo times a second. At another
point let a similar apparatus discharge the negative pole loo
times a second; then between these two places there will be
a greater difference of potential than in other directions, and
a series of earth currents, loo per second, will flow from one
to the other. Any sensitive electrical device, a galvanometer
or a telephone, will be disturbed at this latter station by
these currents, and any intermittence of them, as can be
brought about by a Morse key in the first place, will be seen
or heard in the second place. The stronger the discharges
that can be thus produced, the stronger will the earth currents
be of course, and an insulated tin roof is an excellent terminal
for such a purpose. I have generally used my static telephone
in my experiments, though the magneto will answer.

"I am still at work on this method of communication, to
perfect it. I shall soon know better its limits on both land
and water than I do now. It is adapted to telegraphing be-
tween vessels at sea.

"Some very interesting results were obtained when the
static receiver with one terminal was used. A person stand-
ing on the ground a distance from the discharging point could
hear nothing; but very little standing on ordinary stones, as

22 RADIODYNAMICS

granite blocks or steps; but standing on asphalt concrete, the
sounds were loud enough to hear with the telephone at some
distance from the ear. By grounding one terminal of the
induction coil to the gas or water pipes and leaving the other
end free, telegraph signals can be heard in any part of a big
building and its neighborhood without any connection what-
ever, provided the person be well insulated."

Explanation of Dolbear's System

Although Professor Dolbear's circuit arrangements re-
semble somewhat those of Marconi, his system lacked the
essential features which, later, were applied so successfully,
namely, electrical oscillations of high frequency at the trans-
mitter and suitable detecting apparatus at the receiver.

Dolbear's results were clearly those of electrostatic induction
and not, as he believed, due to conducting effects through
the earth; the earth connections merely served to furnish
one side of an electrostatic condenser, the other sides of
which were supplied by the elevated conductors; the same
results can be secured by using insulated metallic capacity
areas, now known as counterpoises, instead of the earth as
the lower halves of the radiating and receiving aerial systems.
This is made plain by a study of the drawings taken from his
patent specification.

The functions of the elevated condensers, H, Hi, and H2,
and of the battery b (Fig. 4), are not evident, since the under-
lying principle upon which the whole system is based does
not explain their necessity. This principle is nothing more
than a statement of the laws of electrostatic induction; it
can best be understood by a study of the properties and
action of the circuits with the imnecessary apparatus omitted.
At the transmitter we then have a voice-controlled source of
high potential, one end of which is earthed and the other con-
nected to an insidated elevated conductor. At the receiver

TELEGRAPH SYSTEMS

we have a similar elevated conductor earthed through an
electrostatic telephone. When sound waves impinge on the
microphone of the transmitter, fluctuating currents are set
up in the primary of the induction coil; these produce fluctu-
ating potentials at the terminals of the secondary winding,
which are conducted to the elevated capacity area; the
latter with the earth forms an electrostatic condenser with
the intervening air as the dielectric. The electrostatic field
of force of this condenser extends radially out and down-
wards from the aerial wire
in curved lines, as is graphi-
cally shown in the accom-
panying diagram. (Fig. 5.)
Now .if an insidated body,
such as the elevated wire
of the receiver, lies within
this field of force, potentials

stress lines of
Electrostatic Field

Elevofed Ctiar^

Conductor

Eart-h'

Fig. 5.

will be induced on it, the amplitude of which varies in unison
with the variations of potential on the transmitting aerial
wire.

Since the earthed plate of the electrostatic telephone in
the receiver remains constant at the earth's potential and
since the other plate is connected to the elevated wire and
subject to the inductive action of the transmitter, a varying
difference of potential is therefore set up between the plates,
with a consequent variation of attraction between them.
One of the plates, which is a diaphragm of flexible metal or
of some such material as thin sheet mica covered with a tin
foil conducting area, is therefore made to vibrate and repro-
duce sounds produced at the transmitter.

Lowenstein^s Electrostatic Telegraph

Mr. Fritz Lowenstein, a consulting and research engineer
of New York, engaged in radio research work, suggested a

24 RADIODYNAMICS

similar method of signalling to short distances in igi2.
This was based principally upon the marvellous sensitiveness
of his potential operated receiving device. It could be used
advantageously with the (magneto) telephone and was
therefore adapted for both telegraphy and telephony; the
telegraphic system, however, gave the best results for dis-
tance; telegraphic signals were sent, with his apparatus, from
his laboratory at 115 Nassau Street to the Liberty Build-
ing at the corner of Nassau and Liberty streets, about a
half mile distant. The transmitter consisted of a 20,000- volt
transformer, the primary of which was energized by a 500-
cycle alternating current. One terminal of the secondary
was grounded to the water pipe system; the other was con-
nected to a single, nearly vertical conductor (No. 8 stranded
copper), the upper well-insulated end of which extended to a
drop wire from the top of a three hundred-foot office building
nearby.

The receiving station near the top of the Liberty Building
consisted of a one hundred-foot length of bell wire suspended
from a pole out one of the windows and connected to Mr.
Lowenstein^s ion controller detector,* the other terminal of
which was grounded to the water pipes. The sensitive
telephone connected to the instrument clearly indicated the
Morse signals sent out at the transmitter. ^ These were made
by opening and closing the primary circuit of the transformer
with a Morse key.

Passing over the work of Thomas A. Edison, W. F. Melruish,
C. A. Stevenson, Professor Erich Rathenau, and others, we
come to another serious attack on the problem of wireless teleg-
raphy, which was executed in a masterly way by Sir William
Preece, engineer-in-chief of the postal telegraph system in
England.

* A potential-operated, ionized gas-detector and amplifier for radio-
telegraphy, radiotelephony, and wire telephony.

TELEGRAPH SYSTEMS

Preece's Induction-Conduction System

Preece's system was a combination of three previously
existing systems, namely, earth conduction, electrostatic
induction, and electromagnetic induction. Although it is
certain that each of these three phenomena played a part in
the transmission of the signals, their relative importance has
not been definitely determined. A brief explanation will
serve to make his method clear.

^he signals were transmitted between two long, horizontal
wires, one at the transmitter and one at the receiver. These

Condenser ' '^Lhten'mg-ln' Keij

r3-

Transmitting
Interrupter

Transniittinq

Battery
Hlllllllllllll—

-^Cartti

Receiving Teleptione

Fig. 6.

Earth 4-

wires were supported parallel to one another on telegraph
poles and were connected to earth plates of considerable area
at their two ends. The diagram. Fig. 6, shows the con-
nections at each station, which is a combined transmitter and
receiver.*

The pulsating currents through the sending wire and the
earth produce a variable electromagnetic and electrostatic
field, which induces a fluctuating E.M.F. in the receiving cir-
cuit. This is indicated by sounds in the telephone. The in-
duced currents are also augmented by the currents conducted
through the earth itself.

* The use of a "breaking-in" key in this circuit will be found very inter-
esting to practical operators since a number of inventors, within the last few
years, have brought forward this principle as novel for use in radio systems.

26 RADIODYNAMICS

It has been shown that the hemispheroidal mass, repre-
sented by the lines of current-flow from one plate to the other,
can be replaced electrically by a resultant conductor of defi-
nite form and position. This is illustrated in Fig. 7, where
L is the line wire, PP the earthed plates, POP, PAP, etc.,
the equipotential Knes of current-flow, and R the resultant
conductor. The induction effects occurring between two such
circuits are therefore the same as if they were composed
entirely of metallic conductors of the same physical and
electrical characteristics as the line wires with their result-
ant earth conductors. At Loch Ness, where the parallel
wires were about three miles long, the calculated depth of the

Fig. 7.

resultant earth conductor was about nine hundred feet. This
arrangement of parallel line wires with earthed ends therefore
gave all the advantages of signalling between huge, single-turn
coils, with the increased effect due to earth conduction, and
without the almost insuperable diflSculties involved in con-
structing such coils above the earth.

In March, 1898, this system was permanently established
for signalling between Lavernock Point, on the mainland,
and Flat-Holm in the Bristol Channel, a distance of over
three miles. Fifty Leclanche cells and an interrupter fre-
quency of four hundred makes and breaks per second were
used for transmitting, and a telephone served as the receiving
indicator. The signals were very distinct, and it is said a speed
of forty words a minute has been attained without diflScidty.

CHAPTER V
ELECTROMAGNETIC WAVE SYSTEMS

The profound speculations and mathematical researches of
Maxwell on the electromagnetic nature of li^t, followed by
the brilliant work of Hertz and his successors, are so familiar
to the scientific public that a brief r6sum6 of the evolution of
the art is here sufficient.

Again we see that radio signalling, like most wonders of
science, has not been an invention, in the popularly accepted
meaning of the word, but rather a gradual, step-by-step de-
velopment in which many prominent men of science have

Fig. 8.
, EE is the glass tube. P, P, the connectors, and M, the filings.

played a part. Maxwell's theories, published in 1865, laid
the foundation, and Hertz, by a long and carefully executed
series of experiments, paved the way; Hertz's successors,
men who foresaw the practical value of these discoveries,
utilized the material he laid bare for the production of a
serviceable means of communication.

The greatest need in the extension of Hertz's work to
greater distances, was a receiving wave detector of high
sensitiveness. A crude form of such a detector had, as early
as 1866 been used by S. A. Varley as a lightning arrester.
In 1890 Prof. E. Branly of the Catholic University of Paris
rediscovered the eflFects, already utilized by Varley, of Hertzian

27 •

RADIODYNAMICS

waves on the conductivity of metallic filings. He also ob-
served the restoring or decohering effect of light tapping on
the filings tube. In 1893 Sir OUver Lodge repeated Hertz's
experiments, using the '^Branly tube/' or ''coherer/' as he

Capadtyf^rea pQ-j Capacify Area\

Coherer

Fig. 9.

called it, in place of the micrometer spark gap in the Hertz
resonator. Branly's coherer is shown in Fig. 8. Lodge's
apparatus, connected for reception of signals, is shown dia-
grammatically in Fig. 9. With this apparatus he was able to
observe Hertzian waves at distances up to about 150 feet.

Early Work of Nikola Tesla

Nikola Tesla, after completing the application of his dis-
covery of the rotating magnetic field to electric motors in
1888, turned his attention to the problem of transmitting
electrical energy to a distance without wires. His earliest
plans were to transmit energy not only in small amoimts, for
purposes of communication, but also in amounts sufficient for
industrial purposes.

The first public annoimcements of these plans were made in
February and March, 1893. He delivered lectures before the
Franklin Institute in Philadelphia, and the National Electric
Light Association in St. Louis. However, in 1891, he had
already described and shown, in a lecture before a scientific
society, a method of lighting an electric lamp at a short dis-
tance without connecting wires. High-frequency oscillations
were used in these experiments, but the power of the apparatus
was small in comparison with that of his later lectures and
experiments.

ELECTROMAGNETIC WAVE SYSTEMS

In these lectures he expressed the conviction that: "It
certainly is possible to produce some electrical disturbance
sufficiently powerful to be perceptible by suitable instruments
at any point on the earth's surface."

Describing his plan in detail he says:

*'Assiune that a source of alternating currents be connected
as shown in the accompanying diagram (Fig. 10) with one of its
terminals connected to earth (convenient to the water mains)
and with the other to a body of large surface, P. When the
electric oscillation is set up, there will be a movement of electri-
city in and out of P, and alternating currents will pass through
the earth, converging to or diverging from the point C, where

7) @

Fig. 10.

the ground connection is made. In this manner neighboring
points on the earth's surface within a certain radius will be
disturbed. But the disturbance will diminish with the dis-
tance, and the distance at which this effect will still be per-
ceptible will depend on the quantity of electricity set in motion.
Since the body P is insulated, in order to displace a considerable
quantity the potential of the source must be excessive, since
there would be limitations as to the surface of P. The condi-
tions might be adjusted so that the generator or source, 5, will
set up the same electrical movement as though its circuit were
closed. Thus it is certainly practicable to impress an electric
vibration, at least of a certain low period, upon the earth.
Theoretically it should not require a great amount of energy
to produce a disturbance perceptible at great distance, or even

30 RADIODYNAMICS

all over the surface of the globe. Now, it is quite certain that
at any point within a certain radius of the source, 5, a properly
adjusted self-induction and capacity device can be set in action
by resonance. Not only can this be done, but another source
5i, similar to S or any number of such sources, may be set to
work in synchronism with the latter, and the vibration thus
intensified and spread over a large area; or a flow of electricity
produced to or from the source 5i, if the same be of opposite
phase to the source 5. Proj)er apparatus must first be pro-
duced, by means of which the problem can be attacked, and I
have devoted much thought to this subject." .

Tesla continued his investigations along these lines and in
1898 had already developed apparatus of great power giving a
pressure of four million volts and discharges extending through
sixteen feet. At that time and even today this is considered
remarkable. From 1899 to 1900 he continued his investiga-
tions and in 1900 he published, in the Century Magazine, a
long article of absorbing interest and of great suggestiveness on
*'The Problem of increasing Human Energy." Therein he
described and illustrated with actual photographs his appara-
tus for producing pressures of over twelve million volts and
capable of delivering energy at the rate of seventy-five thou-
sand horse-power.

Professor Popoflf^s Receiver

Professor Popoflf, in a communication to the Physico-
Chemical Society of St. Petersburg, in 1895, described a
form of receiving apparatus designed by him for the study
of atmospheric electricity. His circuit arrangement which is
shown in Fig. 11 is different from that of Lodge in that one
terminal of the coherer is grounded, and the other is connected
to a vertical conductor extending above the housetop. Here
is introduced the well-known method of utilizing the electric
signal bell for an automatic decoherer. Professor Popoff also

ELECTROMAGNETIC WAVE SYSTEMS

used a form of tape recorder which automatically recorded
the duration of the electrical disturbances in the atmosphere.
This apparatus and circuit arrangement is precisely the same
as that used by Marconi in his early experiments. That
Popoff foresaw the possibilities of his receiver for Hertzian
wave telegraphy is clearly evidenced by the concluding para-

FlG. II.

graph of a paper read before the Institute of Forestry of
St. Petersburg. *'In conclusion/' he says, *'I may express
the hope that my apparatus, with further improvements,
may be adapted to the transmission of signals to a distance
by the aid of quick electric vibrations (high-frequency oscilla-
tions) as soon as a means of producing such vibrations possess-
ing sufficient energy is found."

Marconi's Early Work

With Hertz's oscillator and Popofif's receiver Marconi began
his experiments on his father's estate near Bologna, Italy, in
1895. Although only 22 years of age he had already acquired
much knowledge of Hertzian waves, having studied imder

32 RADIODYNAMICS

Professor Rosa of the Leghorn Technical School, and ac-
quainted himself with the published writings of Professor
Righi of th6 University of Bologna. After a year of experi-
menting Signor Marconi went to England and filed, in the
Patent Office of Great Britain, an application for a patent,
which was duly granted.

Later Improvements

Improvements in both the more efficient generation and
reception of the electromagnetic waves have, since 1895,
chiefly engaged the attention of radio investigators. Among
the more important advances may be mentioned the intro-
duction of the Tesla high-frequency transformer for coupled
circuits by Lodge and Braun, instead of the direct spark-
excited antenna of Marconi; the discovery and adoption of
detectors suitable for use with the telephone; the introduction
of alternating current and high spark frequencies for trans-
mission; the utilization of Wien's discovery of the quenched
spark gap; and the more recent attacks on the problem of
selectivity. The recent work of Fessenden, Alexanderson,
and Goldschmidt on the direct production of high-frequency
alternating current of continuous amplitude for electric wave
telegraphy and telephony, is worthy of mention.

CHAPTER VI

POSSIBLE CONTROL METHODS FOR RADIO-
DYNAMICS — SOUND WAVES

Every teledynamic system ha^ two principal parts, namely,
(i) the apparatus for the transmission and reception of the
controlling energy, and (2) the apparatus or mechanisms to
be controlled. This broad subdivision applies to such simple
forms as the telegraph, where the energy-transmitting medium
is a metallic conductor, and the receiver a relay controlling
a soimd-produdng mechanism, as well as to the very com-
plicated systems utilizing the ether as the connecting link.

Of these two divisions the first is to us by far the most
important, if for no other reason because of the difficulty it has
presented in the practical solution of such representative
problems as torpedo control. It therefore demands careful
consideration, especially with reference to a proper selection
of the kind of radiant or other energy to be used.

The following table gives some of the most important forms
of radiant energy in ether and air, their vibration frequencies,
and detecting means capable of actuating mechanisms:

Waves

Frequency per sec.

Detector

Acoustic

16 to 35,000
50,000 to 2 billions
2 to 4000 "
4000 to 8000 "
8000 to ?

Vibratory relay-
Hertzian wave detector

Hertzian

Infra-red, or heat

Visible

Thermoelectric cells
Selenium cells

Ultra-violet

Trigger vacuum tube.

Besides these radiant energy means we may mention
earth conduction, electrostatic induction, and electromag-
netic induction.

34 RADIODYNAMICS

Choice of Control Energy

A nximber of important factors must be taken into con-
sideration in order to make the best choice of these several
control methods. Although the Hertzian wave system is
employed in nearly all of the suggested applications of radio-
dynamics, and is to all appearances the most reliable and
best, who can say that any one of these other possible methods,
if it received the proper attention, would not be much simpler,
and at the same time still more reliable?

Reliability is the factor of prime importance in the abso-
lute and accurate control of a dangerous weapon like a torpedo,
travelling, as it does, at a speed of between thirty and forty
miles per hour and carrying large quantities of highly ex-
plosive material. Simplicity, freedom from accidental or
intentional interference, and cost are other points which
demand careful thought. The maximum range at which
control is necessary, and indeed possible, is limited by vision.
This, in clear weather, does not exceed eight miles, for even
with a good binocular the torpedo cannot be seen beyond
that distance. In cloudy or stormy weather the operations
may be limited to two or three miles. This does not mean
that the usefulness of the wirelessly directed torpedo is
limited to calm, clear weather, for any attacking fleet or ship
would be subject to the same conditions, inasmuch as the
distance and accuracy of their fire is greatly affected by the
condition of the sea and weather.

Difficulties to be Overcome

The reader may think of the four-thousand mile accom-
plishments of modern radiotelegraphy and immediately con-
clude that the problem of getting a suflScient amount of
energy to the vessel is one of comparative simplicity. On
the contrary this is one of the chief difficulties, and it has only
lately begun to be surmounted.

SOUND WAVES 35

The following table will serve in a rough way to show the
comparison between transmitted and received energies in
various types of electrical energy- transmitting systems:

Watts transmitted Watts received Ratio

Power line lo^ lo* i

Cable telegraph i io~® lo"*

Telephone iq-* iq-* io"^

Radiotelegraphy lo^ lo-* io~**

From this table it may be seen that of the one hundred kilo-
watts used at a high-power radiotelegraphic transmitting
station but one ten-trillionth part is received at a distance
corresponding to the maximum working range, ix., the
range at which the received power is measured in hundred-
millionths of a watt. This range in daylight is usually in the
neighborhood of three thousand miles, but is subject to con-
siderable variation from day to day and from season to season;
the night range is also very much greater than the day range
during those parts of the year when atmospheric disturbances
cause the least amount of interference.

In long-distance radiotelegraphic sets the transmitter is of
such power (25 to 100 kw.), as would be excessive for torpedo
control in coast defence. But far more important than this
is the fact that the telephone, which is used as the receiving
indicator in wireless telegraph sets, will give readable signals
under an impressed e.m.f., of less than one-millionth of a volt,
while to trip the most sensitive relay under ideal conditions
requires about one-thousandth of a volt e.m.f. applied to
its terminals. Under the conditions of shock and vibration
aboard a small vessel in a rough sea the restoring spring of
such an instrument must be set under sufficient tension to
prevent the making of false contacts; the sensitiveness is
thereby reduced to from one-fifth to one-tenth of its highest
value. From these values we can readily see that a radio-
telegraphic receiver may easily be as much as 5000 times as

RADIODYNAMICS

sensitive as the type necessary for the absolutely reliable
control of mechanisms. Practically all systems of wireless
signalling depend for their long-distance operation on this

Fig. 12.

Prof. Fesseniden's submarine sound signalling apparatus used to detect the

presence of submarines. {Published by permission.)

extraordinary sensibility of the telephone; when used with a
relay the distance over which they are operative likewise de-
creases tremendously.

Sound Waves in Radiodynamics

The employment of sound waves in air for radiodynamics has
not been productive of any noteworthy results. Submarine

SOUND WAVES

Signalling, however, has been developed to the point where
the transmitting bell signals have been received at distances

Fig. 13.

Operator sending submarine sound signals with the Fessenden apparatus.

{Courtesy of the American Magazine.)

up to about 25 miles. Prof. R. A. Fessenden, one of the
pioneers and authorities on radiotelegraphy in the United

RADIODYNAMICS

States, signalled across Massachusetts Bay during the spring
of 1914, with a submarine sound wave apparatus which he
invented. Figs. 12, 13, 14 and 15 show Professor Fessenden
and various parts of his submarine signalling system. These

Fig. 14.
Vibrating steel diaphragm used as both transmitter and receiver in the Fessen-
den submarine signalling system. {Courtesy of the American Magazine.)

photographs are reproduced through the courtesy of the
American Magazine.*

Although little has been done with this signalling system
in adapting it to the severe requirements of torpedo control,
its possibilities are not unworthy of consideration.

The fact that most steamships, war vessels, and submarine
boats are now equipped with submarine signalling apparatus
is ample proof of the practicability of this system for fog and

* For further details of submarine signalling apparatus see: Jour. Am.
Soc. Nav. Engrs., Aug., 1914; Mar. Engr. and Nav. Archt., May, 1914; Proc.
Am. Inst. Elec. Engrs., July, 191 2.

SOUND WAVES

warning signalling. As practiced, a submerged bell, electri-
cally operated, is used as the transmitter, while a submerged
DMcrophone transforms the received sound waves into elec-
trical effects observable upon a telephone receiver; this re-
ceiving apparatus is in all respects the same in principle as
the ordinary telephone which we have in our offices and

Fig. 15.
Professor Reginald A. Fessenden taking observations on the sound waves sent
out by submarines. {Courtesy of the American Magazine.)

homes. An electric ear of this kind is usually installed on
each side of the vessel, and two telephones provided in the
pilot house for the observer. By switching from one to the
other of these the general direction of the transmitter can
usually be determined, since the receiving microphone on the
side of the boat nearest the bell will give the stronger signal.
When the signals are of equal strength in both telephones the
direction of the bell at the dangerous reef can be determined

40 RADIODYNAMICS

by swinging the ship. The practicability of apparatus based
on such an energy transfer method although not assured is
not wholly uncertain. One advantage of no mean impor-
tance is that the torpedo could be entirely submerged, offering
no target for the enemy's gun fire. Every other system ex-
cept earth conduction in practice would require a portion of
the receiving apparatus to project above the water.

By utilizing sound waves of frequencies below the audible
limit (i6 per second), the control impulses could not be
detected by the enemy unless they were provided with special
apparatus for that purpose. If such a transmitter be used
with timed mechanical elements in connection with current
amplifying devices at the receiver, it is possible that an
extremely simple and effective system of control could be
developed.* The torpedo, although invisible, could be ac-
curately located by means of two submerged microphones,
which would respond to signals sent out by the torpedo
itself. This scheme has been used in the European War
to detect the presence of hostile submarine boats. The
principal difficulties to be met in the use of submarine
soimd waves for torpedo control are the interfering signals,
which the enemy might easily send out, and the very weak
electrical effects produced by the transmitter at battle-range
distances. The former is an extremely difficult problem.
The latter might be overcome by using a simple form of
amplifier, such as De Forest's.

* Such a scheme was described by the author in a lecture on The Wirelessly
Directed Torpedo, before the Indianapolis-Lafayette section of the American
Institute of Electrical Engineers in October, 1913.

CHAPTER Vn
INFRA-RED OR HEAT WAVES

Omitting Hertzian waves for the present we come to the
infra-red rays as a possible means of effecting mechanism
operation at a distance. The great sensitiveness of the
bolometer, thermo-pile, and other thermal and thermo-
electric detectors suggests the use of these rays as a form of
wave energy capable of serving our needs.

No mention of the use of radiant heat for operating dis-
tant switches has been found in scientific literature. As a
means of telephoning to short distances, however, it was
among the first to be suggested, as previously stated.

Stimulated by the accounts of the extreme sensitivity of
radiant heat detectors and of their use in the measurement of
stellar radiations, the writer has given some thought to the
possibility of using heat waves as a control agency in a system
for the wireless direction of torpedoes.

Let us consider first the general advantages and disadvan-
tages of such a control energy, assuming that we have generat-
ing means of such power and receiving detectors of such
sensitiveness that we are able to control switches at useful
distances.

One of the first advantages, and perhaps the greatest, lies
in our ability to direct this energy at will. By means of the
highly-polished, parabolic surfaces of such metals as silver
and zinc, we can direct practically the whole of our generated
energy into a beam of parallel rays. Surfaces of silver and
zinc, when well polished, will absorb no more than two or three

42 RADIODYNAMICS

per cent of the incident radiant energy, the remaining ninety-
eight or ninety-seven per cent being reflected.

In order to secure the advantages of direction by the use of
parabolic reflectors, we must confine our source of heat to a
comparatively small area. But if the area be small the rate
at which the energy is radiated per imit of area must be
correspondingly large. A high radiation rate per imit of area
can only be obtained with a high temperature. In order then
that we may be able eflSciently to utilize heat radiations we
must have first, a source of easily controlled energy which can
readily be converted into the energy of radiant heat; second,
a means of developing an extremely high emission rate per
unit area; third, a means of limiting the radiation to a small
area; and fourth, a properly shaped reflecting surface of
material suitable for directing the heat energy developed into
a beam of parallel rays. Disregarding our primary assvunp-
tion, we must in addition be able to project these rays upon
a swiftly moving receptor ^t five miles distance mth suflScient
efi^ect to produce definite, mechanical movements at will.

These requirements are admirably met in our present high-
power searchlights. Electricity as a prime source of energy
lends itself easily to our needs because of its extreme flexi-
bility; the electric arc as a means of transforming this energy
into heat is not only extremely efficient, but fulfills the require-
ments of small area and very high temperature as well. The
energy in the visible portion of the electric arc spectrum does
not exceed ten per cent of the input energy; but with this we^
are not particularly concerned, since a "black body" receiving
surface will enable us to convert practically all of the radiation
incident upon it, including, besides all of the infra-red, the
visible, and most of the ultra-violet also.

The energy emission rate per unit of area, which is a
function of the energy density per unit of crater surface, is
exceedingly high; the energy density may reach twenty-one

INFRA-RED OR HEAT WAVES

and one half watts per square millimeter, and the temperature
may rise to the vicinity of three thousand eight himdred
degrees Centigrade. Moreover the energy of the high-tem-
perature portion is limited to a comparatively small value
by the low coefficient of thermal conductivity of the electrode
material. This allows a suf-
ficiently close approach to
the "point source" ideal de-
sired with parabolic re-
flectors, for practical utility.
Electric searchlights, or
"projectors," as they are fre-
quently called, have been
built with parabolic reflecting
mirrors sixty inches in di-
ameter. Such a projector of
the type used in the United
States Navy is shown in Fig.
i6. The power of these
projectors can easily be
raised to fifteen or twenty
kilowatts. Were it necessary,
heat-wave generators of this
kind could be constructed
ha\'ing a capacity for trans-
forming an electrical energy
of one hundred kilowatts

into the energy of radiant heat. The infra-red radiations of
the electric arc may be increased by the addition of barium
chloride to the arc electrodes.

Fig. i6.
Sixty-inch projector used with radio-
d3niamic torpedoes. (Published by per'
mission of General Electric Co.)

Invisibility

A searchlight transmitter can be installed directly on a
harbor or coast line and so masked as to be completely in-

44 RADIODYNAMICS

visible to ships several miles at sea. The electric power would
preferably be generated at a central power plant and trans-
mitted over a hidden high-tension transmission line to a
number of these hidden control stations. By means of step-
down transformers (and rotary-converters if it is necessary to
use direct-current arcs), the high tension line currents fur-
nished by the central station would be transformed to currents
of proper potential and power for the operation of the high-
power, electric-arc, heat-wave generators.

Control operators at each hidden transmitter would be in
constant communication with each other and with the military
head of the harbor defenses in order that the control operations
might be constantly in the hands of the operator in the most
advantageous position with respect to the attacking war vessels.

Selective Operation

Since heat waves as a control agency, unlike Hertzian waves,
sound waves, electromagnetic and electrostatic induction, or
earth conduction, can be directed at will, their use demands
no consideration of the selectivity problem, the solution of
which has ever been practically unattainable under the con-
ditions imposed in torpedo control. Although it is possible
to produce Hertzian waves with fronts perpendicular to the
direction of propagation, the diflSculties involved in construct-
ing reflectors of sufficient size for the wave-lengths necessary
are very great from a practical point of view. Other means
have been developed for directing Hertzian waves, among
which may be mentioned the radio-goniometer of Bellini and
Tosi, but in practice it has been found that the power of siich
transmitters is limited.

In order to prevent the enemy from projecting the beams of
their own searchlights onto the receiver of our torpedo, the
latter is provided with a gyroscope which serves to keep the
receiving heat detector always facing toward our own trans-

INFRA-RED OR HEAT WAVES 45

mitters on shore and away from the enemy at sea, a screen of
opaque material on the side toward the sea providing means
of intercepting the rays from the enemy's lights. This same
gyroscope at night serves to keep from the view of the enemy
at sea, the screened signal lights on the torpedo, which at all
times are plainly visible from shore, and which are automati-
cally operated by the control apparatus within the torpedo.
Their purpose is to permit the control operator on shore to
follow the direction of the torpedo without keeping his trans-
mitting searchlight directed upon it, and thus in continuous
view of the attacking ships, and at the same time automatically
to signal back the operations occurring on the torpedo.

The rays of the searchlight are invisible in bright daylight
imless an observer be directly in their path; this is desirable,
inasmuch as it prevents the enemy from locating the screened
control stations. At night the powerful light is a distinct
advantage in locating any attacking ships, and, when neces-
sary, in following the torpedo itself. Should it become
necessary to have the control station invisible during the night
as well as by day, suitable ray filters would be necessary.
Substances which will screen off or absorb the visible radia-
tions and allow the longer infra-red waves to be transmitted,
that is, substances which are said to be "diathermanous," are:
black fluorite, smoky quartz, black glass, and a strong solution
of iodine in carbon disulphide; gases not near the point of
condensation are also highly diathermanous.

Dispersion and Atmospheric Absorption

The best of our present-day searchlights are not capable of
producing strictly parallel rays. The non-parallelism usually
amounts to at least three or four degrees. Because of this
dispersion the beam of a searchlight which at the mirror is
sixty inches in diameter, may be five hundred or a thousand
feet in diameter at a distance of five miles. It is obvious,

46 RADIODYNAMICS

therefore, that the illumination intensity directly in front of
the searchlight will bear to the illumination intensity at five
miles a ratio equal to the ratio of the respective areas of the
beam at these points; this equals the ratio of the squares of
the radii of the beam at these points. In the case of the sixty-
inch searchlight, assuming that at five miles the beam has a
diameter of one thousand feet, this ratio would roughly equal
twenty-five thousand to one. It is possible, however, that
the dispersion could be reduced by a more careful attention t0
this useless waste of energy. No necessity has yet arisen for
such a reduction in searchlights as now used, since it is desir-
able to illuminate the entire length of modem, five-hundred-
foot battleships at such distances.

Atmospheric Absorption

Some of the energy of the rays is absorbed in the atmosphere.
If the vibrating rates of the atmospheric gases are equal to
any of the vibration rates in the projected waves, part of the
energy of those particular waves will be absorbed. In this
connection it may be possible so to choose the electrode
materials for the arc that vibration rates produced in the arc
will not be equal to those of the atmospheric gases, thecjeby
evading the energy losses due to this cause.

In foggy or rainy weather the atmosgSierii| absorption would
be materially increased because water is not very diather-
manous. It is also true, however, that in such weathei*battle
ranges are materially decreased because of the decrease in the
limit of vision, which, in turn, is brought about by mist, rain,
or fog. It is difficult to foretell whether or not the two would
decrease at the same rate.

Receiving Radiant Heat Detectors

The development of sensitive radiant heat detectors has
followed several distinct lines corresponding to the varying

INFRA-RED OR HEAT WAVES 47

phenomena of radiant energy in the form of heat waves whose
lengths are longer than 0.77 m- The length of the visible waves
lies between 0.77 m and 0.39 m, those above 0.39 m being in the
ultra-violet.

Those effects of radiant heat which have been used in the
production of sensitive detecting instruments may arbitrarily
be classified as follows:

I Volumetric expansion (chiefly of gases).

2. Thermoelectric currents.

3. Resistance change in electrical conductors.

4. Stresses in rarefied gases.

5. Linear expansion of solids.

As an example of the first may be mentioned the micro-
radiometer of Weber.* This instrument is a combination of
a differential air thermometer and a Wheatstone bridge. A
thin glass tube which contains at its center a drop of mercury
surrounded on both sides by a solution of zinc sulphate, con-
stitutes two arms of the bridge. Platinum electrodes sealed
in the bulbs at each end of the tube dip into the zinc sulphate
solution. One of the bulbs, which is made of an opaque
non-conducting material, and coated inside with lampblack,
is fitted with a fluorite window. When radiant energy enters
through the non-absorbing, fluorite window it is absorbed by
the contained gas and by the lampblack. Thus heated, the
gas expands and pushes the liquid toward the opposite bulb.
This changes the relative lengths of the mercury colimm and
of the solution between the platinum terminals; the balance
of the bridge being upset, a deflection of the galvanometer
consequently occurs. This instrument was stated to be
sensitive to a temperature change of one millionth of one
degree.

* Weber, Archiv. Sci. phys. et Nat. (3) 18, p. 347; 1887.

48 RADIODYNAMICS

Thermoelectric Detectors

These radiant heat detectors may be divided into two groups,
namely, those in which the detector and the sensitive gal-
vanometer with which it is used are two separate and distinct
instruments, and those in which the two are combined into
a single instnmaent. The thermopile is representative of the
first group, and for the second we have the radiomicrom-
eter.

Let us first consider the thermopile. From the very be-
ginning of radiant energy measurements, the power of this
form of wave energy in the ether for developing electric
currents in circuits containing junctions of dissimilar metals,
has found wide application. Tyndall, Rubens, and other
pioneers in this domain secured very satisfactory results with
the thermopile, in spite of its great heat capacity. Rubens-
has described* a linear thermopile consisting of twenty junc-
tions of iron and constantin wires about o.i mm. to 9.15 nam.
in diameter (resistance 3.5 ohms). When used with a gal-
vanometer having a figure of merit of i = 1.4 X 10""^® amperes
(resistance = 3 ohms, period = 14 seconds), a deflection of
one scale division indicated a temperature change of i^.i X
io~*. A candle at five meters gave a deflection of 10 cm. or
250 cm. at one meter. The area of the exposed face of the pile
is about 1.6 cmT^. The heat capacity was such that its
stationary temperature was reached in less than seven
seconds.

If /> = the thermoelectric power in nMcrovolts per degree
( = 53 X io~* volts for iron and constantin), n = the number
of junctions exposed, and r = the internal resistance, of the
thermopile; and if we combine the pile with a galvanometer,
which, with an internal resistance of w ohms, gives a deflection
of m millimeters per microampere, then a deflection of i mm.

* Rubens, Zs. fur Instrumentenkunde, 18, p. 65; 1898.

INFRA-RED OR HEAT WAVES 49

indicates a change in temperature at the junctions of At degrees
when

npm

The highest efficiency is obtained when the resistance of the
thermocouple is equal to the combined resistance of the
connecting wires and of the auxiliary galvanometer.

Coblentz has described* a linear thermopile of bismuth-
silver junctions which had a heat capacity low enough to attain
ninety-two per cent of its maximum temperature in two
seconds. It has a completely opaque surface, this novelty
being secured by a series of overlapping receivers; it has a high
sensitivity; the materials are sufficiently strong to withstand
rough usage; it is quick acting, and yet sufficiently massive to
permit operation in the open without being disturbed by the
cooling effect of air currents.

The efficiency of the thermocouple is such that one micro-
watt of radiant power produces about 0.02 microvolt per
thermojimction in the thermopiles of bismuth-silver, or in
larger units i watt = 0.02 volt.

At present we have no exact knowledge of the mechanical
equivalent of the radiations of large searchlights, but for
simlight we have accurate data. Upon the reasonable assump-
tion that we can develop searchlights which, with the aid of
collecting and concentrating means at the receiver, will produce
received effects at five miles equal to those produced by sim-
light without such concentrating means, we may proceed to
make calculations on a simlight-source basis. Mr. W. W.
Coblentz has kindly made for the author the following cal-
culations on the current developed in a thermocouple with
sunlight as a source:

* Various Modifications of Bismuth-Silver Thermopiles Having a Con-
tinuous Absorbing Surface, Scientific Papers of the Bureau of Standards, No.
229, p. 132

50 RADIODYNAMICS

The solar radiations reaching the earth's surface are about
i.o to 1.2 gr. cal. onT^ per minute = -^ gr. cal. cm? sec."^,
or about ^^^ watt per cm.2 per second. For a quick-acting
thermopile the receiver has an area of about 0.04 cmT^, so that
when exposed to simlight the amoimt of radiant power inter-
cepted is

— - = 0.003 watt.
IS

This would produce 0.016 X 0.003 = 48 X 10"^ volt, or a rise

in temperature of about one-half degree centigrade.

By increasing the number of couples to 100 and placing the
whole in vacuo, the sensitivity could be increased 200 times.
The e.m.f . developed would then be 200 X 48 X 10"*, or very
nearly o.oi volt. Within recent years relays have been
perfected which will operate with impressed voltages of
approximately 0.003 volt. A factor of safety is therefore,
apparent, since the received current is three times that re-
quired for operation. These rough calculations indicate that
heat-wave control systems are quite within the range of
possibility.

Our calculations are based on the assumption that we can
produce, at five miles, thermoelectric effects equal in magni-
tude to the effects produced at the earth's surface by the solar
radiations. It is probable that this assumption can be realized
in practice. Even if this were not possible, we have means of
increasing the received effects so that a much smaller heat
intensity at the receiver would produce the desired results.
The De Forest three-stage amplifier is capable of amplifying
minute received currents to from five hundred to a thousand
times their original strength. These amplifiers operate best
with pulsating or alternating received currents. It would be
a simple matter to use a current interrupter of either the
motor-driven or vibrating-buzzer type for breaking up the
direct current produced in the thermopile. This would intro-

INFRA-RED OR HEAT WAVES $1

duce some compKcations. The thermopile and galvanometer
relay, with an auxiliary relay capable of handling larger
currents would, however, form a very simple and reliable
receiver.

^ Radiomicrometersi Bolometersi and Radiometers

Three other well-known types of radiation detectors are the
radiomicrometer, the bolometer, and the radiometer. The
radiomicrometer, which was invented independently by
d'Arsonval and Boys, consists essentially of a moving-coil
galvanometer of a single-loop with a thermo-junction at one
of its ends. It is, as previously stated, a combined thermo-
couple and galvanometer.

The bolometer is simply a Wheatstone bridge, two arms of
which are made of very thin, blackened, metal strips of liigh
electrical resistance and high temperature coefficient, one or
both of which are exposed to radiation.

The radiomicrometer, because of its great delicacy, is not so
suitable for radiodynamics as the separate thermopiles and
galvanometer relays. The bolometer is an extremely sensitive
radiation detector, but careful precautions must be observed
in keeping at a constant temperature the air in which it is
contained so as to avoid the drifting of the zero position of the
auxiliary galvanometer.

The radiometer of Crookes, a scientific toy which may be
seen in many jeweller's windows, has been modified for radiant
energy measurement. Nichols* has described a radiometer
consisting of two blackened vanes of platinum attached to a
horizontal arm and suspended in a vacuum by a quartz fiber.
Although instruments of this type will detect a change in
temperature of one one-m'llionth of one degree, their extreme
delicacy and sluggishness make them less suitable than ther-
mopiles for radiodynamics.

♦ Phys. Rev., 4, p. 297; 1897.

RADIODYNAMICS

The Tasimeter

Edison's tasimeter consists essentially of a vulcanite rod and
a microphonic contact. The vulcanite rod, which has a high
coefficient of linear expansion, is made to exert a pressure on
the microphonic contact by means of a screw press. A slight
expansion of the rod, brought about by a slight increase in
temperature, causes a change in pressure on the microphonic
contact, and consequently a change in its resistance. When
the microphone forms one arm of a Wheatstone bridge the
apparatus becomes a very sensitive radiation detector.

Edison used a solid rod of hard rubber in compression
against two blocks of carbon, as shown in Fig. 17. Owing to

Compression Adjustment

Fig. 17.
Simple form of Edison's tasimeter.

the large mass of rubber in the rod and to the low coefficient of
conductivity of hard rubber, this form is sluggish in its action.
The author has modified this instrument in order to increase
its sensitiveness and to decrease the period required to attain
its maximum temperature under the action of a given intensity
of received radiation. The modification consists substantially
in substituting a sensitive telephone microphone of the carbon
granule type for the blocks of carbon, and in replacing the
hard-rubber rod with a thin strip of hard rubber. This strip
is maintained in tension by an adjustable spring. The arrange-
ment of microphone, hard-rubber strip, and adjusting screws
is shown in Fig. 18.

INFRA-RED OR HEAT WAVES

This instrument, when connected in circuit with a battery
and ammeter, will readily indicate a change in current suflSicient
to operate a relay, if influenced by the heat of a bxmsen burner
at a distance of one meter. Although not lacking in sensitive-
ness, heat detectors of this type are subject to vibration, jars,
and sounds; a weakness which disqualifies them for radio-
dynamics, particularly in the radiodynamics of torpedo control.

Thermostats

In an endeavor to provide a sensitive, quick-acting, heat-
detecting instrument which will close a circuit directly without

Fig. I 8.

the aid of a sensitive relay, the author has experimented with
various types of thermostats. After experimenting with
mercury-in-glass thermostats designed especially for quick
action, with composite-strip thermostats of both the straight
and spiral types, and with alcohol, mercury, and gas ther-
mometers, the conclusion was reached that a modification of
the differential gas thermometer would be far more suitable
than the other types, because of its high sensitiveness and
rapidity of action.

The most satisfactory form thus far produced is shown in
Fig. 19. The general scheme of this type of instrument was
suggested to the author by Prof. E. S. Ferry, of Purdue

RADIODYNAMICS

University. In the drawing A is the heat absorber of thin,
lampblacked platinum, B and Z), two glass gas-chambers,
connected by a glass tube of small bore; B is lampblacked
inside. Jlf is a thread of mercury; W-W are water or alcohol
columns whose function is to prevent the mercury from moving
by jumps under the action of the expanding gas in B; and C-C
are contact wires of platinum sealed into the glass tube so as
to make contact with the mercury thread. ,

If heat rays fall upon the platinum disc -4, they are absorbed
and their energy appears as a rise in the temperature of A.

Fig. 19.

A has a very small heat capacity because of its low specific
heat and its thinness, and it therefore requires but a small
amount of heat energy to raise its temperature. Since
platinum has a high coefficient of thermal conductivity, the
heat is rapidly conducted to the gas in the closed chamber B.
This chamber is so designed that the distance from the plati-
num to any part of the enclosed gas is small, in order that the
conduction-time-lag through the gas may be a minimum.
The inside of B is lampblacked in order to prevent escape of
heat by radiation through its walls. The temperature of the

INFRA-RED OR HEAT WAVES $$

enclosed gas therefore rises rapidly to the temperature of the
absorber. This gas, which is especially chosen for its maxi-
mum coefficient of volumetric expansion and its minimum
specific heat, expands and pushes back the liquids in the tube.
The mercury M will then short-circuit the two (!onnecting
wires C-C, thus closing the external circuit. .If the source of
heat be removed the order of actions is reversed. The, ab-
sorber A then becomes a rapid and efficient radiator, and the
heat of the gas in 5 is dissipated through conduction to and
radiation from the platinum disc A, Any change in normal
temperature, i.e., the temperature of the air in which both A
and D are contained, will not cause any appreciable change
in position of the mercury thread because pressures will be
produced in the two gas chambers which are equal and opposite.

W-W consist of some non-conducting liquid of low specific
gravity. Without some such steadying means the mercury
thread will have a tendency to move in jumps. The specific
gravity should be low in order that a slight difference in the
levels of the two columns will not require a great difference in
pressure between A and D. If mercury were used a relatively
large difference in pressure between A and D would be neces-
sary in order to produce a motion of M sufficient to bridge
contact wires just above the normal position of the mercury
surface.

The author has constructed thermostats of this type which
will operate satisfactorily in strong sunUght, an exposure of
from one to five seconds being sufficient to produce the maxi-
mum deflection of the mercury thread. The complete periods
were considerably less than twice these values.

These results can probably be improved upon. The author
has experimented with gases containing vapors of alcohol,
ether, carbon tetrachloride, and similar liquids whose satu-
rated vapors have a high coefficient of volumetric expansion.
The results of these experiments are promising.

56 RADIODYNAMICS

A differential gas thermostat of this type, if developed to the
proper sensitiveness, would be as near the ideal of a heat-wave
receiver as we can hope to reach. Its extreme simplicity and
ruggedness, and the absence of the usual sensitive relay are
its chief advantages; all other types of receiving apparatus,
whatever the nature of the control energy, require, besides
various other apparatus, a sensitive relay, usually of the
galvanometer type; this, in turn, requires a more rugged relay
for handling the electrical energy used in performing the
various operations aboard torpedoes.

Heat-wave control systems, we may therefore state, are
not only within the range of possibility but of probability as
well. The extreme simplicity and ruggedness of both trans-
mitter and receiver, the absence of masts and other aerial
targets, the satisfactory solution of the interference problem,
the near approach to complete invisibility of both transmitter
and torpedo, and the almost indiscernible form of the control
energy are factors that commend heat waves as a connecting
link between the shore and the wirelessly directed torpedo.

CHAPTER Vin
VISIBLE AND ULTRA-VIOLET WAVES

As shown by the table, the visible waves vary in frequency
from 8000 billions down to 4000 billions per second, repre-
senting the various colors from violet, down through blue,
green, and yellow to red, and including all the thousands of
intermediate shades. Quite apart from the various optical and
chemical effects these waves are capable of producing, their
chief interest to us lies in their ability to effect changes in
the electrical characteristics of various substances. These
changes can be utilized for the operation of delicate indi-
cating or relaying instruments. Selenium, described more
fully in a subsequent chapter, is the most important of these
substances affected by light. Systems of telegraphy and
telephony based on its peculiar property of changing its
electrical resistance under the influence of light, have occupied
the attention of numerous scientific men since Willoughby
Smith's discovery of that property in 1875. But no ac-
count of its application to torpedo control can be found.
The writer ventures here to present some experimental data
and observations made by him, especially in view of the
possible adoption of a light-wave selenium control system for
the Hammond dirigible torpedo.

From a number of selenium cells of varying types and re-
sistances two, made by Dr. Korn of Vienna, were chosen.
The sunlight and dark resistances of one of these were 2000
and 5200 ohms respectively; of the other, 1300 and 3000 ohms.
These two cells were to be used in selective light telegraphy
tests and it was decided first to learn the applied e.m.f.

RADIODYNAMICS

range in which the cells operated with the greatest sensitive-
ness and smallest inertia. The 2000-5200 ohm cell was first
tried. It was connected in a series circuit with a battery and
microammeter, and with a potentiometer for accurate regu-
lation of potentials. The operation was much better with

V
>

'20cm-^^*^

,i'cp^ 1 1 Y^

Yoff-' Sensitiveness Curve

*forny

Seteni

umCe

UNO,

1.4 VOLT DRY CELLS
Fig. 20.

the highest current density permissible with the micro-
ammeter, so it was decided to use a millianmieter and higher
potentials. Potentials as high as 25 volts were used and the
results are given in the curve of Fig. 20. This shows graphi-
cally the relation between applied voltage, current, resist-
ance, and the current change between light and darkness.

VISIBLE AND ULTRA-VIOLET WAVES 59

The current change is the factor of principal importance. It
is noted that this value increases directly as the voltage, and
that the highest value corresponds to the highest value of cur-
rent density permissible. It was learned that if this exceeded
five or six milliamperes for an hour or more, the cell would
get out of order, and a telephone inserted in the circuit in-
dicated that the current was varying at a rate, of several
thousand per second. The sound was an irregular hissing
or frying noise, resembling closely the soimds in a radio re-
ceiver due to heavy atmospherics, or that heard in an ordi-
nary telephone during the progress of a thimder storm in
the inmiediate vicinity. The tests were made with a i6-c.p.
carbon filament electric light, at a distance of 50 cm.

The 1300-3000 ohm cell, which we shall designate No. 2,
was given a similar test under slightly different conditions.
The i6-c.p. light was placed at a distance of 10 feet, and a
five-inch condensing lens was used to increase the intensity
of illimiination on the active surface of the cell. The curves
of Fig. 21 show the relation between the e.m.f., current,
resistance, and current change with the No. 2 cell.

By a comparison of Figs. 20 and 21, it is readily observed
that the combination of the No. 2 cell with the condensing
lens was more sensitive at a distance of 10 feet than the
No. I cell at about 20 inches. The indications of the milli-
ammeter showed that when the cells were brought from
darkness to light the resistance dropped very quickly to
about two-thirds the Resistance change value, and then to
the lowest value in about five or ten seconds. From this
observation it is obvious that the cell would operate much
more efficiently for slow variations in the light intensity than
for rapid, such as are used in light telephony, since the lagging
part of the current change represented by the change occur-
ring, say one-fiftieth of a second, after a given change in illumi-
nation, would be of no value where the variation frequency

RADIODYNAMICS

exceeded 50 per second. It would seem, therefore, that the
higher characteristics of the human voice, which may reach
vibration rates of five thousand per second, would be re-
produced with less distinctness than the lower characteristics.
This is actually the case with light telephony as well as with

4 6

1.4 volt cells

Fig. 21.

wire telephony, the inertia being too great to permit the re-
sistance to follow the rapid variations in the light's intensity;
in wire telephony, however, the inertia is mechanical rather
than electrical, except in very long distance lines where
the capacity comes into play. It was also found that the
cells were more sensitive in some parts of the active surface

VISIBLE AND ULTRA-VIOLET WAVES 6l

than in others. The five-inch condensing lens was used to
furnish a small spot of intense light with which to explore
the surface of the cell. When the diameter of this spot was
made about one-sixteenth of an inch the best results were
secured. The surface of the selenium, to secure this con-
dition, was placed very near the focal point of the lens. The
sensitive spots could then be accurately located, and in some
places the cell was several times as sensitive as in others. Ex-
perimental investigations of the cause of this spot sensitive-
ness were not made.

A test was made with the No. 2 cell with a view to de-
termine the possible value of a selective light signalling and
radiodynamic control system devised by the writer. In these
tests a light interrupter was used to effect the periodic illumi-
nation and darkening of the selenium cell at rates up to 300
per second.*

Fig. 22 illustrates the general arrangement of the apparatus
as well as the results of the test. The light used was a 4-c.p.
carbon filament electric lamp, and the interrupter was, as
shown, similar to those used on motion picture machines; it,
however, had a much larger number of blades, and, as shown
in the sketch, was attached to the shaft of a fan motor. A
rheostat and tachometer permitted variation and exact
knowledge of the speed, so that any desired interruption fre-
quency could be obtained.

At the receiver a three-inch condensing lens was used with
the selenium cell. The latter was connected in circuit with
a variable battery, a milliammeter, and the primary of a
ferric transformer. The secondary of the transformer was
connected in a series oscillatory circuit with another liunped
inductance and variable capacity of the Korda type. By
varying the capacity or inductance of this circuit, it could be

* In later tests an arc light supplied with alternating current of from 60 to
600 cydes was used to furnish the periodically fluctuating light.

RADIODYNAMICS

brought into resonance with the periodicity of the light in-
terruptions. The oscillatory currents set up in this circuit
by the action of the pulsating currents in the selenium cell
circuit, when the two were in resonant operation, were less
than one ten-millionth of an ampere. Since that value did
not give a satisfactory telephone signal, an amplifying device,

5 45

</)
u
q:

^ 50
<

o 15

' l^' J^~^~^7^''^TV\C -m^ '^' Condenser ! •§

D.C. I I ^ITf fienci^ri/ Vapor Tube ^ ^}p<r viV /1>^«*^ xJ- H ' W ^ " ** S

• -^'<^^«' /ort---^^ — n^^'^ J_l

... .^ I vK

/iofor ^'' Light Interrupter //j?*^ia

Bunsen

Amplifier

200 250

FREQUENCY

450

Fig. 22.
Resonance curve of the author's selenium, selective, light-wave, radlodynamic

control system.

due to F. Lowenstein, was used, which, in turn, effected the
operation of a telephone of the high resistance type, and a
microammeter. With this arrangement the telephone signals
received when the circuit and light interrupter were in res-
onant operation, were very loud, the interruptions of the
light being heard as a clear musical tone, equal in frequency
to the frequency calculated from the speed of the motor, and

VISIBLE AND ULTRA-VIOLET WAVES 63

the number of blades on the shutter disc. The microam-
meter mdicated a signal current of about 50 microamperes
as the maximum value for resonance adjustment.

The selectivity was so good that it was difficult to keep
the apparatus in tune, owing to slight variations in the speed
of the shutter motor caused by changes in the line voltage.
The resonance curve shows very clearly the degree of selec-
tivity obtained. It is observed that when the frequency of
the interruptions was between zero and about one hundred,
the selective circuit was forced to vibrate in its own period,
and the effect oii the receiving instrument was practically as
great as when the purely resonant operation occurred. The
amplitude of the superimposed fluctuating current^ on the
normal dark current in the selenium cell circuit, which con-
tained a considerable ferric inductance, was probably 50 times
greater for frequencies, say, below icx), than for frequencies
in the neighborhood of 800, the natural frequency of the
circuit during the test. This accounts for the fact that the
indicator currents were so high with the forced operation in
comparison with those of resonant operation. The funda-
mental vibration rate of the circuit at this particular setting
was approximately 345 complete periods per second. The
selectivity no doubt could have been improved upon by a
better design of light interrupter, which would produce
sinusoidal variation in the selenium cell's resistance, and by
using inductances of less resistance than were used in this
experiment.

Several electric lights in the room, including a mercury-arc
light and a gas light placed directly between the condens-
ing lens and the four candle-power light, did not mate-
rially affect the strength or quality of the received signals.
It is believed that the distance could have been considerably
increased or the intensity of the signal light reduced without
greatly reducing the strength of the received signals. The

64 RADIODYNAMICS

telegraphic signals were sent with an ordinary Morse key
connected in series with the signal light and operated according
to the Morse or International codes.

Selective mechanically tuned elements were also tried in
place of the tuned electrical circuit and an even greater
degree of selectivity was obtained. These tuned elements
were of the different types due to Ruhmer, Lowenstein, and
Pickard, and are known as monotone amplifones or selective
reed relays. A complete description is not permissible.
The electrical circuit is, however, to be preferred for practical
use on account of its nice adjustability and ease of handling,
and because it is not, like the amplifone, subject to jars or
sounds.

Although these experiments were rather encouraging, later
tests made with a 24-inch searchlight during both day and
night furnished conclusive evidence that, with the illumina-
tion furnished by such a source of light and the best selenium
cells procurable, the operative range of such a system would
not exceed a distance of one mile. The tests were therefore
discontinued.

Ultra-violet Radiations

Ultra-violet light has a powerful effect in facilitating the
discharge of electrons from negatively charged conductors and
entirely overcoming the hindrance ordinarily experienced.
The light waves may be conceived as shaking up the neutral
atoms condensed aroimd the electrons and setting the latter
free.

Suppose we have two conductors in a vacuum at a difference
of potential of, say, 300 volts, and that ultra-violet rays are
made to fall on the negative wire. The negative electrons
are set free to enter the vacuum and are repelled by the
negative conductor; at the same time they are attracted by
the positive conductor, and, since nothing prevents them,

VISIBLE AND ULTRA-VIOLET WAVES 6$

they pass from one to the other, and with a velocity of ap-
prpximately 6600 miles per second. (See Fig. 23.)

Although we have but little data oh distances at which these
effects are observable, we know that they can be brought
about, and a method of applying this property of ultra-violet
light at once suggests itself.

In the "Electrische Zeitung," July, 1898, Prof. E. Zickler
proposed to use this property of these radiations for teleg-

->J(?<7>&/*-*-

Vacuum Tube

4— ^4

V 'I'lni'i y

rTTtmn-

Ultra Violet Rays |ti|]Jli]

Fig. 23.

raphy. He succeeded on a small scale and believed that with
a 2S-ampere lamp and suitable reflectors, good results were
possible over several kilometers. His proposal was based on
an at first inexplicable phenomenon observed by Hertz. In
the course of his experiments on resonance it was observed that
the intensity of the sparks at the detector was greatly increased
by placing a screen between it and the exciting spark. Later
the curious effect was attributed solely to the ultra-violet
rays emitted by the exciting discharger.

For such simple apparatus as that required for exploding
mines where but one energy impulse is required, the problem
is quite simple, requiring only an electric explosive cap in
series with the battery and vacuum tube. When the rays
are directed upon the negative electrode of the vacuum tube
the discharge occurs immediately, and the current passing

66 RADIODYNAMICS

through the electric cap effects the ignition or detonation of
the explosive material.

For the control of complicated mechanisms, however, a
relay and some form of electric switching device are required.

Although ultra-violet rays have all the advantages of in-
audibility, invisibility, and simplicity of generation and
reception, in view of the known fact that the earth's atmo-
sphere very strongly absorbs their p)ower it is very probable
that operation of such a system at useful distances would
involve considerable difficulty.

CHAPTER IX
EARTH CONDUCTION

The early suggestions of Steinheil and their subsequent
application, as previously outlined, have been quite seriously
considered as a very simple substitute for the comparatively
complicated Hertzian wave apparatus for torpedo control.
In view of the simplicity of the apparatus, and of the all-
important problem of selective control offered by earth con-
duction telegraphy, experiments were conducted by the writer
in Gloucester harbor (19 12) to determine roughly its value for
torpedo control.

The general plan of the proposed system is shown graphi-
cally in the accompanying drawing (Fig. 24).

Heavy insulated wires lead from the submerged plates to
the station, where, by means of a switchboard, heavy currents
can be sent between any two of the plates. The six different
current fields thus capable of production are shown in the
drawing by the curved lines.

The receiver comprises two conducting plates, one at the
bow of the torpedo and one at or trailing behind its stern, with
insulated conducting wires extending inside to the terminals
of a sensitive relay. The necessity of so many current fields
is obvious when we consider that we must be able to operate
the sensitive relay regardless of the torpedo's direction of
motion, i.e., the direction of the current field must correspond
to the direction of extension of the receiving plates. If means
for accomplishing this are not provided it is possible to lose
control of the vessel altogether.

The first thing to determine in these experiments was

RADIODYNAMICS

whether or not it would be possible to transmit enough energy
to the receiver, at distances up to the limit of vision, with

Submerged

mrerfomfey

\ \^^

\ /

///,

^ y

If/ ^

Submerge

Contra! Sfaf-ion
Fig. 24.

apparatus of such power as is consistent with practical con-
siderations. With this end in view, apparatus was arranged
as shown in the sketch (Fig. 25), which also shows the received

20 Amp.

200

DJsfance behveen Sending Pis. ZOO Ft.
- Receiving " 6 Ft

- IOSclFI
Sending - ?S •' -

^ . Area each

*--^ •• . - . Sending " ZS •' -

I w deceived current values shovtn arel(y*AmpL

Fig. 25.

currents indicated by the Weston microammeter, for different
positions of the receiving boat in the current field. This in-
strument was connected directly between the receiving plates

EARTH CONDUCTION 69

which were fastened at the bow and stern of a ten-foot row
boat.

The transmitter consisted of a 25-volt, 120-ampere-hour
storage battery connected to two copper plates having an
effective area of about 25 square feet each. One of these
plates was the regular ground for the radio set aboard an 8-ton
house boat; the other was fixed to the bottom of a row boat,
moored about 200 feet distant.

A No. 16 bell wire, extending from the mast of the house
boat down to the row boat, served to complete the circuit.
The results are clearly shown in the drawing.

A very curious, unexplained phenomenon was observed dur-
ing these tests. The readings were taken on transmitted im-
pulses of about two seconds duration, with intervening periods
of rest, and were made in response to signals, by an assistant
on the house boat, who opened and closed the circuit bekveen
the battery and the overhead line wire extending to the distant
sending plate. In this way one battery terminal was con-
tinually connected to the earth plate beneath the boat.

In addition to the usual earth current — these currents may
be found almost anywhere on the surface of this earth and
were in this case of course independent of the sending battery
— readings were obtained which varied up to 50 microamperes
according to the position and direction of extension of the
receiving boat; and these readings gradually increased as the re-
ceiving boat neared the house boat. When the house boat plate
was disconnected from the storage battery the received current
dropped to the normal value. Signals could thus be sent, up
to distances of about 50 feet, simply by making and breaking
the connection between the battery and plate, with absolutely
no current flowing from the battery. The arrangement of
apparatus and results are shown in Fig. 26.

The following day (Sept. i, 1912) further tests were made
with increased power and distance. The transmitting current

RADIODYNAMICS

was obtained from a bank of four no- volt, 50-ampere mer-
cury-arc rectifiers, regulated by a series resistance, and meas-
ured by an ammeter. The respective areas of the transmitting

\< so Ft'

<?o

(/[OQ

25 V.
H91J

CopperGivund
P/afe

Fig. 26.

plates as well as the distances between them are given in the
drawing (Fig. 27). The leads to the earth plates of the
transmitter were composed of twenty-foot sections of No. 20
copper strips, one and a half inches wide, soldered together.

f/ov.ac.

400

too

400

Distance between Sending Plates 400 Ft
** ' " Receiving ' B Ft

Area each " * _ ^ ^9'^^%..

Senctina - SQ &, ISSqSt
Received current values shov/n onr IQr^Amp.

Fig. 27.

The maximum current obtainable was 50 amperes, and the
received current values shown were secured with this trans-
mitting current.

On Oct. 3, this distance was again increased, this time to
approximately 1000 yards between the sending plates. Fig.
28 shows the results of this test.

EARTH CONDUCTION

The received current values resulting from these different
tests show that, in a line between the two transmitting plates,
the position of the receiving plates for weakest signals is
midway, and for strongest, nearest either of the plates. With

Dish nee between Sending PI3. 3000 Ft.
Receiving - 30 Ft
Area each " - BSq.Ft.

" . ■ , Senefing - SO - " .

received current values shown are JO'%Ttp

Pig. 28.

a transmitting power of over five kilowatts, the received
currents at the position of minimum signal strength (which is
the distance determining factor), that is, at a distance of less
than one-half mile, were no more than sufficient to operate a

Fig. 29.

sensitive relay of the type necessary for torpedo control.
These results were far from encouraging and the tests were
discontinued.

A somewhat different scheme due to Mr. H. Christian
Berger, an electrical engineer of New York, was next tried.
The transmitting energy was a high-frequency oscillatory cur-

72 RADIODYNAMICS

rent, and the receiver was of the regular radio type, with two
earth connections instead of one earth and one aerial.

The earth plates were of copper, loo and 25 square feet
area, respectively, separated 400 feet, and connected, as shown,
in series with the oscillating condenser circuit. A hot wire
ammeter in this circuit indicated a current of four amperes.
The primary energy was delivered to the condenser circuit by
a 3-kw., no to 20,000- volt, 6o-cycIe transformer. (See Fig. 29.)

The receiver connections, illustrated in the small drawing
at the right, are those of a common radiotelegraphic receiver .
with the exception previously noted. The distance between
the receiver grounds was about 250 feet, and the distance
between the two sets of grounds of transmitter and receiver
was estimated at about 500 feet.

Dr. L. W. Austin, head of the U. S. Radio Laboratory in
Washington, D. C, has shown that a radiotelegraphic sender
may exert a very large amount of power for the brief periods
of time during which the condenser discharges.

Considering a condenser of 0.04 mfd., charged to a potential

of 10,000 volts, Q is equal to '— — X 10,000, or 0.0004

1,000,000

coulomb.

The work done in charging such a condenser to that poten-

^. , . , ^ V^C 10,000^ X 0.00000004 . ,

tial IS equal to , or — -, or 2 joules, or

2 2

o- 737 X 2 = 1.47 foot-pounds. It can furnish that amount
of energy in one discharge.

If the condenser is discharged through a circuit of such self-
inductance as will give a wave length of 1000 meters, the
oscillation frequency will be 300,000, and the alternations
600,000 per second. 0.0004 coulomb will create an average
current of 0.0004 X 600,000 = 240 amperes. Were the wave
length much shorter the current would be correspondingly
greater, as is shown by the following example.

EARTH CONDUCTION 73

The above condenser is discharged through an inductance
which will give a wave length of 500 meters. The alternation
frequency of this circuit would then be 1,200,000 per second.
0.0004 coulomb will create an average current of 0.0004 X
1,000,000 = 480 amperes. By this we see that the current
in an oscillatory circuit is inversely proportional to the wave
length.

If the energy of 2 joules stored in the condenser is radiated
in five complete oscillations, the rate of doing work, if the eflS.-

ciency of conversion is unity, is 2 joules in - — ^ — second =

600,000

240,000 per second = 240 kw. This shows very clearly that

although the available energy is very small, the rate of doing

work, i.e., the power of a wireless telegraph sender, may be

very great for a short period of time.

This peculiarity of a condenser discharge is, no doubt, the
basis for Mr. Berger's suggestion. The scheme is distinctly
novel, utilizing, as it does, oscillating currents of high fre-
quency, but with earth conduction, and not etheric radiation,
as the means of transferring the energy.

The tests given this system were very severe in that the
conditions imposed were far from ideal; but at that time it
was believed that if no telephone signals could be received
imder those conditions, the system would be valueless for relay
operation. No signals were received during this test and the
experiments were discontinued.

CHAPTER X

ELECTROSTATIC AND ELECTROMAGNETIC INDUC-
TION—HERTZIAN WAVES

Following the scheme of Dolbear, the author experimented
with electrostatic induction as a possible means of torpedo
control at the Hammond Radio Research Laboratory in 1912.

The transmitter consisted of a 100,000-volt transformer,
especially built for the purpose, energized by alternating
current of from 60 to 1000 cycles. One terminal of the

./«.

Transmitter

Detector "^

Fece'iver

Fig. 30.

secondary was grounded, and the other connected to the
station antenna,* which was insulated for 1,000,000 volts with
Electrose strain insulators.

The receiving apparatus consisted of an antenna,t on the
house boat Pioneer^ connected to a very sensitive form of
potential operated radio detector which will be more fully
described in a subsequent chapter.

Fig. 30 shows schematically the circuit arrangements.

* 300 ft. high, 400 ft. flat top. t 30 ft. high, 20 ft. flat top.

HERTZIAN WAVES

The curve, Fig. 31, was made by taking readings of the re-
ceived currents, as indicated by a Weston microammeter,
connected to the receiving detector. The Pioneer was
started seaward within about a hundred feet of the trans-
mitting station, and readings taken every minute near the
shore; after the steeper part of the curve had been passed
the readings were taken at longer intervals.

400

5300

e/7sfi
<nce-

Jrr£/e
nfens

ctro&i

utic 7
eived

CURRENT Ml

RECEIVED
1

'^ 1

J0(

X)
Dl

20
STAN

OEiN

30
FEET

00"

4d(

Fig. 31. '

An attempt at tuning the receiver to the frequency of the
alternating current used at the transmitter was made by in-
troducing a variable inductance of large value and a tuning
condenser in series with the antenna, and connecting the de-
tector to a point of maximima p)otential in this circuit. Fig.
32 shows this circuit.

The transmitter was then changed to the regular radio
type, the wave length being pushed far beyond the natural
period of the antenna by means of loading inductances in
both open and closed circuits. This was done to increase
the potential to the highest possible value, in order to in-

76 RADIODYNAMICS

crease the distance of operation. With an emitted wave
length of about 3000 meters, the p)otential was slightly in-
creased over that previously obtained with the transformer,
but no material increase in received results was noted.
The group frequency was 120 per second. In order to meas^
ure the electrostatic effects alone, no tuning to the high fre-
quency oscillations was attempted, the receiving antenna being

Anfenna

Iron Core fnducf once

Pdteritio

Tuning
Earth

Fig. 32.

connected only to the detector. The low-frequency tuned
antenna circuit was then substituted for this receiver as be-
fore. The curve obtained in the best series of tests (Fig. 31)
shows that with our very sensitive relay operating imder
working conditions, the . maximum range would be only
up to about 1000 feet, a distance far too short for torpedo
operation. This method of control was also abandoned.

Electromagnetic Induction

Beyond the work of Preece, Trowbridge, Edison, and
others, already mentjioned, very little has been done in the
field of electromagnetic induction for radiodynamics.

The fact that the transmitting and receiving coils or line
wires must be in parallel planes is one of the chief objections
to this system for transmitting energy impulses to a movable
boat.

The writer has not been able to find any accounts of work

HERTZIAN WAVES 77

along this line. Although the difficulties are not in them-
selves insuperable, from a practical point of view they have
been considered too great in comparison with other systems.
No effort therefore has been made to utilize electromagnetic
induction as a means of controlling dirigible, self-propelled
vessels.

Hertzian Waves

ftertzian waves, as every one knows today, are by far the
most imp)ortant means of wirelessly transmitting energy,
either for the communication of intelligence or for the con-
trol of self-acting apparatus of whatever nature. We are
not so much interested in presenting historical matter per-
taining to the very large amoimt of work done since Marconi's
first experiments; nor do we wish to burden the reader with
detailed theoretical or practical considerations of the many
phases of the radio signalling art, it being assumed that he is
sufficiently acquainted with the art as it now stands to under-
stand the accounts of its special application in the compara-
tively new field of radiodynamics; these special applications
will be hereinafter described in sufficient detail to be readily
imderstood by those possessing some knowledge of electricity.

CHAPTER XI

THE ADVENT OF WIRELESSLY CONTROLLED
TORPEDOES

Although the subject of this chapter does not include
torpedoes in general, it is nevertheless important to have
some knowledge of the ordinary torpedo, and some facts
pertaining to its advantages and disadvantages, if we wish to
obtain a clear conception of the wirelessly controlled weapon
now being perfected for modern naval warfare.

The torpedo is claimed to be an American invention, being
said to have sprung from the fertile brain of Benjamin Franklin,
who, during the Revolution, experimented with this then un-
heard of method of marine attack. The first attempt in war
of which we know was made in the harbor of Brest, on the west
coast of France, in 1801, under the orders of Napoleon. This
first test under actual war conditions was made by an Ameri-
can, Robert Fulton, the father of steam navigation. Fulton
used a submarine boat, the drawings and designs of which
have never been published. He is said to have obtained con-
siderable success in his experiments, but he failed in an
attempt to blow up an English man-of-war, whereupon
Napoleon withdrew his support, and the scheme was not
carried into practical operation.

We next hear of torpedoes in the Russian war of 1854,
when one of prodigious power was exploded in the harbor of
Cronstadt, through copper wires connecting with a galvanic
battery on shore.

Again, during our own Civil War, the torpedo made its
appearance in improved form. It was employed for harbor

ADVENT OF WIRELESSLY CONTROLLED TORPEDOES ^g

defense chiefly in and around Charleston. It was also used
with deadly effect during the Spanish-American War, and, in
the hands of the Japanese, inflicted great damage to the
Russian fleet in the battle of Fuishima Straits.

Every modern battleship is equipped with from two to
four torpedo tubes. The United States alone has over 60

Fig. 33.
The first Holland submersible.

torpedo boat destroyers, 30 torpedo boats, and 50 subma-
rines, representing a cost of at least fifty million dollars and
manned by over three thousand officers and men.

The modern torpedo, for the handling of which all these
vessels have been built, is about eight feet long and nearly
two feet in diameter at the largest part. It is propelled by a
compressed-air motor fed from tanks containing air under
about seventy atmospheres pressure, and is kept laterally

RADIODYNAMICS

stable, and on its intended course by a gyroscope. It has a
speed of from twenty-five to forty knots, a range of from one

Fig. 34.
Types of torpedoes.

thousand to four thousand yards, and carries from two to
three himdred pounds of highly explosive material, usually
gun-cotton. It is launched from a 'Horpedo tube," a form

^^^' 35-
Modem U. S. submarines.

of compressed-air gun, which on battleships and submarines
is submerged, and on torpedo boats and destroyers is so

ADVENT OF WIRELESSLY CONTROLLED TORPEDOES 8l

mounted on deck that the missile can be fired in the desired
direction without swinging the ship. Figs. 33 to 39 will aid

Fig. 36.
View of a battleship in a dry dock showing submerged toipedo tube.

in making clearer the explanations relating lo torpedoes and
to the different types of ships upon which they are used.

Fig. 37.
Deck type of torpedo tube used in launching torpedoes from torpedo boats.

Before actually firing a torpedo allowances must be care-
fully made for such variable factors as speed and direction of

RADIODYNAMICS

both the target and the firing ship, the direction and velocity
of the wind, and the condition of the sea.

Fig. 38.
U. S. S. South Carolina equipped with two submerged torpecjo tubes.

The percentage of hits at the extreme range of four thou-
sand yards is not greater than twenty-five; and when the
sea is disturbed, even at much shorter ranges the accuracy is
still less.

The torpedo boats of both surface and subsurface types are
chiefly relied upon to do the torpedoing, and, because of the

Fig. 39.
Torpedo boat destroyer entering Norfolk Navy Yard.

fact that in order to do accurate firing the distances must
not be great, these vessels are subject to the very hot fire
of the enemy's torpedo defense battery of three- and six-inch
gims. The torpedo attacks are, however, usually made under

ADVENT OF WIRELESSLY CONTROLLED TORPEDOES 83

the cover of darkness or fog; this fact, coupled with their
great speed and small size, is their only protection. If they
can approach near enough to discharge accurately a torpedo
before being discovered and illuminated by the searchlights
of the enemy, all is well; but if not, it is probable that their
thin hulls will be riddled with three-inch shells before they
can escape.

The principal advantage of the ordinary torpedo is that
usually with one well-directed shot, a small, comparatively
inexpensive craft carrying from ten to fifty men can totally,
or at least seriously, disable a huge fighting machine like a
modern dreadnought, carrying a thousand men and costing
from five to fifteen million dollars. Its disadvantages are
principally the great risk to human life accompanying its use,
the comparatively poor accuracy of the firing, and the fact
that if a shot is a failure, the five thousand dollar torpedo
cannot be recalled.

In the year 1897, when wireless telegraphy was still in its
infancy, Ernest Wilson, an Englishman, was granted a British
patent on a system for the wireless control of dirigible, self-
propelled vessels. The primary object of this invention was
to provide a weapon for use in naval warfare, which, if in the
form of a dirigible torpedo, controlled from a shore or ship
wireless installation, would be most deadly in its effect on a
hostile fleet. No mention has been found of actual apparatus
constructed according to Wilson's plans.

To Nikola Tesla, probably more than to any other investi-
gator, belongs the credit of first constructing a dirigible vessel
which could be controlled from a distance without connecting
wires. His experiments were begun in 1892 and from that time
on he exhibited a number of wirelessly-directed contrivances in
his laboratory at 35 South Fifth Avenue, New York City. In
1897 he constructed a complete automaton in the form of a
boat (Figs. 40, 41 and 42), which would steer itself in obedience

RADIODYNAMICS

to guiding impulses of Hertzian waves sent out from shore.
On Nov. 8, 1898, he was granted a United States patent on
this invention. In this patent he mentions the use of all

Fig. 40.

Nikola Tesla's telautomaton, controlled by Hertzian waves, which is the first

radiodynamic boat.

forms of control energy including electromagnetic induction,
electrostatic induction, conduction through earth, water, and
the upper atmosphere, and all forms of purely radiant energy.

ADVENT OF WIRELESSLY CONTROLLED TORPEDOES 8$

The drawings, of which there are ten, illustrate in detail the
nature and arrangement of the apparatus. These drawings
were made to scale from the completed model, which he had
in operation at that time.

I '- ~

Fig. 41.
Side view of Tesla's boat.

Wilson's was the pioneer patent in that branch of radio-
telegraphy now known as radiodynamics. Since then a large
number of patents in this field have been taken out by various
inventors, and several of those who have been so fortunate

Fig. 42.
Interior view of Tesla*s model radiodynamic torpedo.

as to secure the means, have developed their respective systems
in the effort to realize their possibilities.

Gardner of England, Wirth, Beck and Knauss of Ger-
many, Gabet and Deveaux of France, Roberts of Australia,

RADIODYNAMICS

and Tesla, Sims, and Edison of the United States have
during the last fifteen years attempted to solve the problem in
a practical way. All of these investigators save Roberts,
Simms, and Edison have applied their systems on boats
intended primarily for torpedoes, which they control by
Hertzian waves. Sims and Edison, with the cooperation
of the United States Government, developed a system for

Fig. 43.
Roberts's (Australia) wirelessly directed airship exhibited in 191 2.

controlling a dirigible torpedo through a trailing conductor,
and Roberts has applied his system to dirigible balloons. Fig.
43 shows A. J. Roberts and his wirelessly-controlled airship as
it appeared on the lecture platform. The twelve-inch induc-
tion-coil transmitter may be seen at the right on the table.
At A is the coherer, tapper, relay, and coherer battery; at B is
a rotary switch of the Tesla type; at C are several cells of a
storage battery and two signal lights; at D are two propelling
and steering motors which are mounted at the ends of a

ADVENT OF WIRELESSLY CONTROLLED TORPEDOES 87

centrally-pivotted, horizontal frame about two feet long.
WTien both are rotating the airship moves directly ahead.
Steering is accomplished by stopping one of the motors. A
single wire about 4 feet long serves as the antenna. The length
of the airship is 15 feet and the weight is approximately 16
poimds. The gas bag consists of four layers of pig intestine.
The intestines. of over 4000 pigs were used in the construction
of this bag. The maximum control distance is about 500 feet.

These inventors have had various degrees of success in
their endeavors to perfect their inventions, but apparently
none have reached the goal. It is true that they have con-
trolled the movements of vessels from a distance without the
aid of conducting wires, but at best the apparatus has worked
spasmotically, unsatisfactorily, and the greatest distance at
which their vessels have been controlled has not exceeded
one-half mile. But why, we may ask, have these able experi-
menters failed to secure the desired results when wireless
telegraphy, the mother of radiodynamics, has made such
wonderful progress?

Oa analyzing the situation we find that early in the art
potential-operated receiving devices, such as the coherer, were
used, which permitted the use of recording mechanisms. As
the art progressed ne;v^ receptive devices were discovered
which, in connection with the marvellously sensitive telephone,
proved the coherer comparatively insensitive and unreliable.
Coherers were then discarded and replaced by the detectors
and telephones, which provided a means of signalling over
vastly greater distances with the same transmitting power as
before. The new detectors, while forming a very desirable
combination with the telephone, were entirely unsuitable with
relays, and, therefore, those interested in the control of
mechanisms were compelled to retain the coherer as the
receiving detector. This is the reason for the poor success
attained in the field of radiodynamics. The coherer, being

88 RADIODYNAMICS

capricious in its action, sometimes operates when the trans-
mitting key is closed, and sometimes when no signals are sent,
possibly steering the boat to starboard when the signal should
have turned her to port, or stopping the engine when full speed
was desired. The coherer, because of its unreliability has
heretofore been the barrier to the full realization of the inven-
tion's possibilities.

CHAPTER Xn
SELECTORS

We have already discussed the possible control methods for
use in radiodynamics. The function of these, as has been
pointed out, is to operate an electromagnetic switch, or relay,
as it is called, from a distance. We have also shown how selec-
tivity in the operation of a relay can be secured by an applica-
tion of the familiar principles of resonance; for example, the
methods of tuning in radiotelegraphy to periodically recurring
characteristics of the emitted wave energy.

Since there are a number of mechanisms to be controlled,
each with a distinct operation to perform aboard the torpedo,
it is evident that we must have either a separate receiver and
relay for each mechanism, or else some kind of selector appara-
tus controlled by a single receiver and relay. As pointed out
by Hammond, we can, therefore, make two broad classifica-
tions of the control systems, namely, (i) monopulse, those in
which a single kind of impulse controls a single relay, which,
in turn, controls a means of selecting the desired circuit, and
(2) polypulse, those in which a different kind of impulse and a
separate receiver and relay are used for each circuit to be
controlled.

A further classification, depending on the type of relay-
controlled selector used by various experimenters, follows;
this classification also has two main heads, namely, {a) those
systems involving the time factor in impulse emission, and
(6) those independent of the time factor.

Under a we have:

(i) Blondel's, Gray's, and Mercadier's methods of con-

90 RADIODYNAMICS

trolling separate mechanisms by the use of tuned mechanical
or electrical elements at the receiver, and a transmitter capable
of transmitting impulses of varying group frequency.

(2) The author's system which utilizes a method of oper-
ating separate mechanisms by impulses of different length.

(3) The author's method of using a transmitter of variable
impulse frequency and a receiver with a solenoid of high self-
inductance in which the current is made to vary by change of
impulse emission rate so that its core can be made to assume
any one of a number of positions.

(4) Gardner's system in which the ratio between the length
of impulses and of the intervening periods of rest is varied, and
in which a solenoid is used at the receiver, its core assmning a
definite position for each value of that ratio.

Under b we may place the following:

(i) Tesla's method which uses one type of impulse to con-
trol a number of different mechanisms, as a clock fitted with
a hand, which, operated from a distance, could be made to stop
on any five-minute point, the hand needing to pause say two
seconds before the energy would be exerted.

(2) Walter's method, which depends on synchronous me-
chanical rotation; as two clocks, one at the transmitter and
another at the receiver, each fitted with a hand, which moved
synchronously over their respective dials, and so arranged that
when the transmitting hand is depressed and stopped, say, at
the figure six, an impulse will be sent out that effects the
pulling down and stopping of the receiving hand which is also
at six, thus closing the circuit; when the transmitting clock
hand is raised, the impulse ceases and both then resume their
synchronous rotation.

(3) There is still another method upon which modern auto-
matic telephone systems are based, namely, the method of
closing any one of a plurality of circuits by sending the correct
number of impulses; for example, we have a square figure

SELECTORS 91

divided into 100 equal squares; beginning at the lower left-
hand square let us number it o, the next above it i, the next 2,
and so on up to 9; then let the square at the right of o be
called I, the next beside it 2, the next 3, and so on to 9; the
squares above these are numbered in exactly the same way,
that is, the columns are all of the same figures. We have a
checker normally at the o position that can only be moved
twice to place it in any square, and only in two directions, i.e.,
up, and to the side. Now in order to get our checker in space
67, for instance, we move it six blocks up and seven to the
side. In the case of the loo-circuit selector illustrated by this
checkerboard, two different sets of impulses are necessary, one
which effects the raising of the contact arm to the desired row,
and another to move it laterally to the position desired.

Among the earliest devices we find that of Tesla, used also
by Orling and Braunerhjelm, Jamieson and Trotter, Roberts,
and Varicas, employing a form of rotating commutator or
its equivalent.

Of these, Tesla's, Varicas', and Roberts' only have been
actually put in practice. Varicas' boat carried out in 1901
the simple steering evolutions required but the apparatus
was quite unprepared to cope with intentional interference.
Roberts, as before stated, applied his system in 191 2 to a
small dirigible gas balloon for theatrical exhibitions. None of
these operations were carried on at any considerable distance,
probably not farther than a few hundred feet, but no authentic
data is available. All employed the primitive filings coherer.

CHAPTER XIII
EUROPEAN CONTROL SYSTEMS

The following extract from an article on ''Telemechanical
Problems in the Wireless World," by L. H. Walter, M.A.,
taken with the kind permission of the author, describes some
of the systems experimented with in Europe during the past
IS years.

Walter's Selector System

"As an example of codal selectors the system devised by the
writer in 1898 may be taken, not because it is considered the
best — for the writer is prepared to admit that in its early
form it left something to be desired — but because it is
practically the earliest comprehensive method, and also be-
cause it has served as a model upon which nimierous later
systems have been foimded, such as those due to Chimkevitch,
to Htilsmeyer, Branley and others. The system was worked
out as a selecting device suitable for any telemechanical, as
opposed to telegraphic purpose, although Righi and Dessau
in their 'Telegraphie ohne Draht,' and also Mazzoto in his
book, describe the writer's arrangement as though it were to
be used for selective wireless telegraphy, like the later system
of Anders Bull, which has many points of similarity. The
original idea involved the use of synchronous rotating discs at
the sender and receiver, both released by the act of sending a
preliminary signal. One complete revolution of the disc then
resulted, if no further impulses were received, and the arrange-
ment was then in its initial receptive state. The receiver disc
comprises a number of contact studs placed on the periphery

♦ 92

EUROPEAN CONTROL SYSTEMS 93

of the disc, corresponding to the code signal selected for one
circuit; these studs are all connected with a safety device. If
during the disc's rotation impulses are received when the
contact brush is exactly on one of the studs so connected, the
safety device has its circuit closer advanced one step for each
such correctly timed impulse, and finally makes an operative
contact when the desired evolution (steering, firing, etc.) is
carried out. Should, however, any impulses arrive when the
brush is not on a codal stud, the safety device flies back to its
initial position, thus preventing the actuation of the apparatus
by unauthorized or interfering impulses. It is well imder-
stood that the transmitter has as many codal discs as there are
circuits to be controlled, and there are a corresponding number
of safety devices. Special relays are also used for the purpose
of stopping an evolution when the next evolution is one which
cannot be carried out without conflicting with the first (e.g.,
'helm to port' and 'helm to starboard').

"Although apparatus of this type was kept at work in the
author's laboratory for several years it has never been fitted
on an actual boat, owing to the fact that the idea appeared to
be before its time, as people at that date were not inclined to
take even wireless telegraphy very seriously. HUlsmeyer's
system, however, which dates from 1906, and is practically
identical with that of the writer, was tried in Germany on a
practical scale, and is said to have proved satisfactory, al-
though it has not been possible to obtain any further particu-
lars. The much-discussed system due to Professor Branley is
also carried out on almost identical lines; his earlier arrange-
ment of 1906 being later completed, in 1907, by the addition
of a safety device like that of the writer."

Gardner's Torpedo Control

"The highly ingenious system devised by J. Gardner ap-
pears to have been the first comprehensive arrangement to be

94 RADIODYNAMICS

put into operation on a practical scale, and has proved to be
one of the most thoroughly reliable methods of controlling
vessels by means of wireless impulses.

"At the first glance the apparatus, which is based upon
an application of Watt's centrifugal governor, appears to be
unlike any of the other systems; but on looking at it from
the point of view of a selecting system it is clear that the
device combines the properties peculiar to both the classes
as already defined. The governor, with its hinged balls
maintained near the axis by means of a spring, is normally
stationary, in which condition the sliding collar on the spindle
is in the rest position, and all circuits are open. When im-
pulses are received from a suitable transmitter, a step-by-
step arrangement causes the governor spindle to rotate; the
governor balls tend to fly out against the action of the spring,
and the collar moves along the spindle, carrying with it a
contact brush which is able to pass over a series of contacts
connected to the various circuits to be controlled. When the
periods of impulses and no impulses are equal, the governor
maintains a constant speed, and it is thus possible, by vary-
ing the relative durations of the impulse periods and the
periods of etheric silence, to make the contact brush pass on
to any required contact, and to maintain it there. At the
highest speed of rotation the firing contact is made.

"One of the chief advantages of this system is that, should
anything go wrong, the *off' position is reverted to auto-
matically, and the torpedo comes to rest.

"By the kindness of Mr. J. Gardner the writer is able to
give a photograph of this interesting dirigible torpedo, which
is the only British wirelessly controlled craft that has stood
the strain of actual tests. Although these trials were carried
out when there was quite a lot of shipping about, there has
never been any mishap and this the inventor attributes to
the simple property possessed by the system of causing the

EUROPEAN CONTROL SYSTEMS

RADIODYNAMICS

vessel to rest when the impulses cease. The short funnel
which will be noticed in the photograph, Fig. 44, is for the
escape of battery gases; the aerial being supported from a
pole which j&ts in the socket just forward of the funnel."

Deveatiz's Dirigible Torpedo Boat

**The method adopted by Lalande and Deveaux is exceed-
ingly simple, but the boat represents the most ambitious
attempt in the history of wirelessly controlled apparatus.
The selector system comprises (i), a circular distribut-

ing switch, having on it the studs pertaining to the cir-
cuits to be controlled; and (2), a circuit closer which only
allows the current to pass when the distributing switch arm
has reached the desired contact stud. In the actual ap-
paratus the distributing switch has twelve studs, of which
nine lead to the nine operating circuits employed; the re-
maining three are distributed among the others and con-
stitute rest positions with a view to saving the switch arm
from having to execute a complete circle each time. Fig. 45
is a diagram of the connections.

''In order to carry out the double function mentioned, an

EUROPEAN CONTROL SYSTEMS 97

electromagnet M is provided which moves forward by one
tooth at each Hertzian impulse, a twelve-toothed step-by-step
arrangement connected to the distributor arm D, During
the period when this arm is being advanced, no closing of the
operating circuits is possible owing to the circuit closer being
opened by means of a projection on the end of the armature of
the electromagnet; this is shown at P. Thus if twelve im-
pulses are received, the distributor would describe a complete
revolution. On the other hand, if the impulses cease after the
distributor has been carried from a rest stud to one of the
operative studs, the circuit closer will complete the circuit after
a brief interval of time, which is caused to elapse owing to the
intervention of a retarding device. This latter consists of a
train of clockwork, which, by virtue of its inertia, does not
allow the circuit closer to operate at once; a delay of twice
the time required for the distributor to be moved forward by
one tooth has been found sufficient. M. Deveaux's paper,
which was published in the Bulletin of the Societe Inter-
nationale des Electriciens, in 1906, will be found to give full
information as to the circuit arrangements, but no illustra-
tions of the boat itself.

*'By the courtesy of M. Montpellier, the editor of TElec-
tricien, the writer is able to make good this deficiency, and
to give two photographs of this craft; Fig. 46 shows the vessel
when hoisted out of the water, and Fig. 47 gives a general
idea as to its appearance and the visibility of its antenna
when afloat; the French cruiser Saint Louis, shown in the
background, was watching the trials which took place off
the port of Antibes in the early part of 1906.

"The boat itself, which weighs 6700 kg., consists of two
cigar-shaped bodies formed of steel plate, one above the
other on the principle of the Sims-Edison dirigible torpedo.
The upper cylinder, 9 meters long by 45 cm. in diameter, acts
as a float; it is provided with two small masts, which serve

RADIODYNAMICS

EUROPEAN CONTROL SYSTEMS

to support the wireless antenna, consisting of five wires kept
at a height of about three meters; and these masts have
lamps about halfway up, for the purpose of facilitating
steering operations. The lower cylinder is ii meters in

Fig. 47.

length, and i meter in diameter, and contains the torpedo-
ejecting tube and a Whitehead torpedo of 450 mm. diameter;
the accimiulator battery and propelling motors are also con-
tained therein. The control apparatus is intended to be
placed in the lower cylinder, where it would be protected

lOO RADIODYNAMICS

from the enemy^s gunfire by two meters of water, but in the
trials the apparatus was placed in a sheet metal box on the
top of the upper cylinder in order to be available should any
adjustments be required. The trials were carried out over
a comparatively short radius, 400 to 1800 meters, but it is
stated that these distances could easily have been exceeded
though to what extent is not said.

*^The transmitting station from which the boat's evolutions
were controlled was on land, and had a five- wire antenna 15
meters in height; but no information is available as to the
actual wave length employed, although, from the size of the
receiving antenna, it was probably very short, of the order
of 80 to 100 meters.'*

Wirth, Beck and Knauss

Remarkable achievements in the line of torpedo control
have been accomplished in Germany, where two immanned
motor boats 33 and 50 feet in length have been steered,
stopped, started, and controlled in every way by electric
waves transmitted from the shore without the use of wires.
The system employed is the invention of C. Wirth of Nurem-
berg. It has been brought to its present stage of develop-
ment by several years of experiment, conducted by Wirth
and his cooperators, the manufacturer Beck and a merchant
named Knauss; it is protected by ntunerous German and
foreign patents.

The ^t success was attained in 1910 with an electric
laimch on a lake near Nuremberg. The vessel was 33 feet
long, and was propelled by a 5 horse power motor, and an
accimaulator battery of 80 volts and 300 ampere-hours.
The first public demonstration was given with this boat in
191 1 before the German Fleet Club; in this demonstration
the unmanned boat fired a signal shot and then set itself in
motion. Travelling at a speed of about 10 miles it was made

EUROPEAN CONiiwif^JSXSTtl^S^ \

lOl

to turn right or left or to stop completely and start again by
the controlling operator in obedience to the requests of mem-
bers of the Fleet Club. Each order was obeyed within from
one to five seconds, and signal lights flashed back the receipt
of the impulses. The manuevers were continued for several
hours.

A boat 50 feet in length was later exhibited in Berlin, at
the invitation of the German Fleet Club. An antenna of

'Antenna

Explosive Head

Receiy^inq and
ContnlApparafyi

steering Nofor

Fig. 48.
Proposed form of Wirth radiodynamic torpedo.

four wires was stretched between the cupola of the Kaiser
Pavillion and the restaurant on the shore of Lake Wann.
The transmitting apparatus which was installed at the
restaurant was of the induction coil type, and was of about
100 watts capacity. The various operations performed on
the boat were accomplished by sending impulses by means
of a Morse key. The boat was equipped with an antenna
of four wires about 15 feet high, a radio receiver capable of
adjustment to different wave lengths from the transmitter, a
distributor or selector, electric steering apparatus, signal
gims, lights, and fireworks apparatus. The tuning of the

I02 /• . : ;

• : :\ jumoi/YNAMics

apparatus could be altered by sending a long signal; this was
for the purpose of evading interference.

The general scheme of the Wirth torpedo is shown in
Fig. 48. The diagram which is here presented in Fig. 49
shows the essential parts of the control system, and the
circuit arrangements. The coherer 38, of the usual filings

type, is connected in the circuit of the battery 37 and a
sensitive relay 39. The armature of this relay, 36, serves to
close a second circuit including the battery 13, by which the
electromagnet 14 is operated. By means of the latter, there
is operated the lever 8 which serves to rotate a ratchet wheel
7 by means of a pawl in the usual way, each time an impulse
is received ; at 40 is a tapper for the coherer. Arriving impulses
cause the ratchet wheel to advance by one, two, three, etc..

EUROPEAN CONTROL SYSTEMS

103

teeth, and as the wheel is mounted integral with a contact
disc, the latter is rotated at the same time. The j&xed brush
thus comes over a metal contactor or otherwise over the in-
sulated part between the contacts according to the position of
the ratchet wheel. Should there be a contact piece under the
brush, the circuit of the battery 4 is closed and one of the
six electric motors, I-VI is set in motion. By the rotation
of the motor there is set working a spring contact device
which will be further mentioned, and such contacts act to

Vm^lk

-■

■

31 i

• * ' •* J

Fig. 50.

close the circuit of the apparatus which is to be finally worked,
such as the movement of the rudder of the boat, etc. A
second motor of the series serves to work another apparatus,
and there is used one motor of small size for each operation
to be carried out. The purpose of the motors is to furnish
a time element device, which allows distinction between long
and short impulses.

Fig. 50 shows the apparatus which is used for two dis-
tinct movements, namely, for steering to right or left. At I
is a relay which is worked by the coherer, and at II the
contact disc before mentioned. At Ilia and Illb are two
small electric motors for making the contacts, this latter

I04

RADIODYNAMICS

being carried out by the spring contact devices IVa and
rVb, one for each motor.

The coherer action sends current impulses by means of the
relay I into the electromagnet of the contact disc. According
to the number of impulses which are sent, we have the brush
placed on a metal contact or in the insulated interval. When
the brush is on one of the uneven-numbered contacts, the
motor Ilia is set working, and it acts on the spring contact
device IVa so as to operate the small contact switch noticed

at the front. Such contact
thus gives current for op-
erating the movement of
the rudder to the left by a
suitable electromagnetic de-
vice. When the brush is
on one of the even-num-
bered contacts the motor
Illb is set rimning, and it
works the corresponding
spring switch IVb so as to
give current for a second
magnetic device, for bring-
ing the rudder to the right-
hand side. The mechanism
of the spring contact device
is arranged on the retarding plan, so that it first sends out a
wave signal which is received at the sending station; two
seconds later it closes the switch.

Should the brush remain but a short time on one of the
contacts, this will give no effect, as the motor takes a certain
time to start up, and thus the motor gives a method of work-
ing by means of long contacts, but not by short ones.

When the brush is on an insulated part of the disc the de-
vice is inactive, and the rudder comes automatically to the

Fig. 51.

EUROPEAN CONTROL SYSTEMS

105

zero or central position. The signal which is sent back to
the shore station is seen on the paper strip of the receiver,
and the operator thus has a check on the working of the ap-
paratus, and can correct any wrong working by subsequent
signals. Wirth's transmitting antenna is shown in Fig. 51.

Dr. £. Branley's Control System

Dr. Branley, of Paris, in addition to various other kinds of
distant control apparatus, devised an instrument with the

Fig. 52.

purpose of protecting the receiver against a continuous stream
of sparks such as the enemy might send out in time of war.

lo6 RADIODYNAMICS

This, like a previous system of Fessenden's, utilizes breaks in
a continuous emission of energy as the signal or controlling
impulses, instead of " makes, '* with periods of rest intervening.
If interfering signals are sent continuously the apparatus can-
not be operated by any other signals, even from the controlling
station, but should the interfering signals cease for a short
time, the controlling operator can perform the desired opera-
tion by making the required number of breaks in his own
continuous stream of signals.

Dr. Branley's protective device consists of a horizontal
disc moved by clockwork, and is kept constantly in rotation
first to the right, then to the left, by electromagnets which
are acted on by distant waves. The rotation of the disc
causes a series of contacts for closing different circuits cor-
responding to the different operations to be performed. The
whole is so arranged that when a continuous stream of energy
is received the disc rotates forward and back. K the dis-
turbing signals cease for a brief period of time the control
operator sends a code signal, which acts upon the disc and its
contacts in such a way that the operation is performed.

In the present type of apparatus the waves are received
upon a new type of coherer which is shown in Fig. 52. It is a
modified form of Dr. Branley's tripod coherer, and is made up
of a polished steel cylinder at the lowest part. It is fitted on
an upright support, and from this three arms hang down by
means of pivots. The arms carry well-rounded steel projec-
tions which bear lightly on the cylinder so as to make the
coherer contact. The whole is enclosed in a vacuum chamber
in order to protect the coherer from the action of the air.
Such a coherer is useless when subject to vibration.

CHAPTER XIV

WORK OF THE HAMMOND RADIO RESEARCH
LABORATORY

Following the rotary switch scheme of Tesla, John Hays
Hammond, Jr., head of the Hammond Radio Research Labo-
ratory at Gloucester, Mass., began his experiments in the
simamer of 1910. No detailed accounts of these first experi-
ments are available, as no systematic method of keeping
records of the work had then been inaugurated, but it is
known that mechanisms designed to steer a small boat were
operated at a distance of three or four hundred feet. This
apparatus, however, was never actually used in a boat for
steering purposes.

Dming the following winter an entirely new set of control
apparatus was designed in New York from Mr. Hammond^s
plans. The object in view was to build a control apparatus,
which could be attached to existing automobile torpedoes.
The coherer receiving set, relays, rotary switch, cut-oflf and
center-stop mechanism, and batteries, were all contained in a
brass tube about one foot in diameter and six feet long.

This apparatus was set up on a float landing about a thou-
sand feet from the transmitting station. An antenna 15 feet
high and 20 feet long was improvised, and after much careful
adjustment, signals were received which were capable of start-
ing, stopping or reversing the steering motor. The transmit-
ting antenna was of the inverted L-type, about 80 feet high
and 200 feet long. An antenna current of about 2 amperes was
registered. The transmitting set was of the Clapp-Eastham
type, 60 cycle, 3 kw.

107

lo8 RADIODYNAMICS

After these preliminary tests the apparatus was set up in
a 1 2-foot gasoline launch, with a 15-foot antenna supported
by bamboo poles. Considerable trouble was experienced in
these tests. Due to the engine vibration, the sensitiveness of
the Seimmans and Halske relay, as. well as the Marconi co-
herers had to be greatly reduced. The Hertzian and inductive
effects from the gas engine caused considerable trouble until
the engine pit was entirely encased in sheet iron; this, however,
did not eliminate the coherer trouble although it decreased
it. The instruments were almost inaccessible for adjustment;
the moist, salt air made matters still worse by corroding the
multitude of contacts. Finally a determined attempt at rudder
operation was made even though the action of the apparatus
was far from what had been expected, and indeed necessary.
The motor in the tube was accordingly connected to the boat's
steering post by chain and sprockets, but when the current
was switched on the motor was found to possess less than
half the power required in turning the rudder hard over when
the boat was under way. Three weeks were spent in futile
attempts to eliminate the difficulties; then the tube and most
of its contents were relegated to what was then the scrap heap,
and now the historical collection.

Simplified Apparatus

Plans were at once formulated for the construction of much
simplified apparatus, which could be thoroughly tested under
conditions in which it could be protected from the weather,
and observed and adjusted while in operation. An old house
boat of about eight tons displacement fulfilled all the require-
ments for a floating laboratory splendidly. She was fitted
with a gasoline engine capable of driving her four knots an
hour, and forty-foot masts for supporting the antenna. This
boat is shown in Fig. 53.

Coherers and relays of highest sensitiveness combined with

HAMMOND RADIO RESEARCH LABORATORY

109

the necessary ruggedness were secured from the electrical
instrument makers in America and Europe. A steering motor
of increased size was procured and mechanically connected
to the steering wheel on the house boat by a worm-wheel
reduction gear; a hand-operated clutch permitted either radio
or manual control of the
wheel.

With this new appa-
ratus installed in the
Pioneer (as the house boat
was afterwards named),
where it was protected
from the weather in an
atmosphere that could be
kept dry and warm by a
coal stove, and arranged
for continual observation
and adjustment while in
operation, the results were
more satisfactory. The
filings coherer, however,
continued to be the chief
source of our difficulties.
Every known remedy for
the trouble was applied to
increase the sensitiveness and reliability, but despite all these,
the sheet iron protection from stray Hertzian and inductive
effects, the protective resistances and capacities for preventing
sudden rise of potential at current-breaking points, — despite
the care exercised in the selection and adjustment of jiggers,
relays, decoherers, etc., — the results were so discouraging that
it was decided to discontinue the use of the filings coherer,
and adopt the Lodge-Muirhead mercury-steel- disc coherer.
Several complete receivers of this type, which had been dis-

FiG. S3'

RADIODYNAMICS

carded from actual service, were purchased from the United
States Navy. These had become obsolete and useless be-
cause of the advent of the telephone receiving sets. The
best of these was installed on the Pioneer and was found to
be more sensitive and reliable than the filings coherer. Fig. 54
shows this receiver as installed aboard the house boat and
Fig. 55 is a detail drawing of the Lodge-Muirhead coherer.

After this change had been made the boat could be kept
under fairly good control at distances up to and over a mile.
It was steered over a prearranged course during both day

Fig. 54.

and night, and in all conditions of sea and weather. The
course was by no means simple, covering, as it did, circles
aroimd several buoys, and a complete circle aroimd the harbor.
Fishing and other vessels were continually moving about the
harbor but no great difficulty was experienced in avoid-
ing them, and, at the same time, keeping on the course.
It was foimd possible to steer the boat against either of
several upright spar buoys a mile from the point of control.
At night lights, automatically controlled by the steering
mechanism, kept the "helmsman" at the transmitting key on
shore informed of the boat's action. A white light would
shine each time an impulse took effect; in this way the con-

HAMMOND RADIO RESEARCH LABORATORY

III

trol operator on shore was immediately informed if the receiv-
ing apparatus or part of the control apparatus had gotten out
of order. As long as the rudder was in the central position no
lights save the required rimning lights were burning. As soon,
however, as the rudder moved to one side or the other a red
or green light on the yard arm would be connected, depending
on the resultant direction of
the boat, and this would con-
tinue to bum so long as the
direction of the steering mo-
tor^s rotation was not reversed.
When the rudder reached the
extreme hard-over position an
additional red or green light
would flash, the two of the
same color remaining illumi-
nated while the boat was turn-
ing in her circle of shortest
diameter. If the direction of
motion was left then the two
lights would be green in color;
if right the color would be red.
As soon as the rudder was
again started back to the cen-
ter the two lights would go
out and a single light of the
opposite color would come on; when the rudder was stopped
at the mid-position by the automatic center-stop mechanism,
the white light would again flash for an instant, signifying
that fact.

The steering of the boat was accomplished by sending
Hertzian wave impulses, which, affecting suitable receiving
and switching devices, controlled the one-fourth horse-power
electric motor mechanically connected to the steering wheel.

Fig. 55.
A is the steel disc with a polished
knife-edge; B is the small cistern of
mercury covered with a film of oil;
K is a leather wiper; H and £ are
the terminals.

112

RADIODYNAMICS

The rudder, by this means, could be made to move to port or
starboard at will, or set at any intermediate position from the
transmitting station.

During the next year some valuable additions were made
for carrying on the experimental and research work; the size

Fig. s6.

of the station was increased, two 330-foot towers (see Figs.' 56
and 57) were erected for supporting the antenna, a battery of
mercury-arc rectifiers was installed to furnish direct current
for the operation of two s-kw. soo-cycle motor generator sets,
two 100,000-cycle alternators, a 24-inch searchlight, and vari-
ous other apparatus. A 40-foot gasoline launch of 150 horse-
power and over 25 knots was built for use as a torpedo, and

HAMMOND RADIO RESEARCH LABORATORY 1 13

Fig. 57.
Installing the antenna system at the Hammond Station.

SB''

1''

^^^^^^^^v

••

_•_

Fig. s8.

114

RADIODYNAMICS

Fig. 59.

other valuable additions were made to the control system,
which permitted a greater range and more reliable operation.

The battery of four General
Electric so-ampere recti-
fiers is shown in Fig. 58.
Fig. 59 shows the s-kw.
Lowenstein Transmitter.

Steering Apparatus

A brief description of the
control apparatus is here
necessary in order to form
a clear conception of some
of the important details.

It has been previously mentioned that a control system is
composed of two main parts: (i) the transmitter and receiver,
and (2) the mechanism to be controlled. The principal parts
of the mechanism, which is the rudder control apparatus, are
the electromagnetically operated reversing switch, the steering
motor, and the source of pov. er.

The rotary switch, shown in Fig. 60, is essentially an
insulating drum fitted with contact pieces; it can be revolved,
step by step, through successive contact positions with a set
of brushes by means of an electron- agnet and pawl and
ratchet. The contact positions and blank or "neutral''
positions alternate; moreover, the contact positions are of
two kinds, one for clockwise rotation of the motor, the other
for counterclockwise rotation. The sequence of positions,
then, as the electromagnet is impulsively operated, is port,
neutral, starboard, neutral, port, neutral, and so on in the
same order.

This is easily understood when the rotary switch is looked
upon as a simple, double-pole, double-throw reversing switch
connected to the armature of the steering motor, the shunt

HAMMOND RADIO RESEARCH LABORATORY 115

field of which is continuously excited. A diagram of this con-
nection is shown in Fig. 61.

Consider the switch in the upper or neutral position, where
the armature is disconnected from the source of power. There

Fig. 60.
Electrically-operated rotary switch designed by the author and used in the
Hammond System of control. Relay at right, drum switch in the center,
and operating magnet at left. S

are two possible ways of closing the switch, corresponding to
the two possible directions of motor rotation. One of these
will, by swinging the rudder to port, cause the boat to steer
aroimd to port; the other will effect starboard motion. The
only difference between these
two reversing switches is that
with the hand type, the motor
after being stopped, can be
made to run in the same direc-
tion again without the necessity of passing over the position
for opposite rotation. With the rotary switch this cannot
be accomplished unless some auxiliary instrument be used to
prevent the motor's rotation while passing over the undesired
position.

:>gjE5

\ Field

Fig. 61.

ii6

RADIODYNAMICS

The steering motor should preferably be of the shunt type
with the field winding continuously energized. This is
important to secure quick action. Motors larger than one-
fourth horse-power cannot well be used with such a controlling
switch because the imregulated starting current becomes
excessively large. Where greater power is required for rudder
operation a pneumatic control apparatus is more effective.
The one-fourth horse-power motor was found large enough for
the 33-mile '* Radio," which had a displacement of about four
tons.

To Rpfartf Switch Magnet

tWilililMilililillliHilililililililililiHiliB

Center Stop Adjustment

jiiiiiiiiiiiiiiitiiiiiiwiiiiiiiiiiiiiiiuiiiiiiiiiii

5tarbo<.rdStop '''Xc/T^ '■<^'"d">«' ,.^J}it^Zn,
■ Adjustment '"->Gbi

— r ►

■Guide Rod .^jf^tPP J

TofiotarySmtcti ^^l<'^^ Base 7o Rotary SyfHcfi
Fig. 62.

The source of power is preferably a storage battery. It
should be of the most rugged type. An Edison 30- volt, 120-
ampere hour battery gave excellent service in the Gloucester
experiments.

A crude, but nevertheless operative, control system can be
made up of these essential parts, since with them the steering
motor, which is mechanically connected to the steering wheel,
can be started, stopped, and reversed, the worm-wheel reduc-
tion gear serving to lock the wheel in any desired position after
the power has been cut off from the motor. The value and
reliability of such a crude controller, however, is much increased

HAMMOND RADIO RESEARCH LABORATORY 117

by the use of auxiliary instruments, which make it possible to
greatly reduce the skill required of the controlling operator.
The cut-off and center-stop mechanism is one of these. It
consists essentially of a threaded shaft bearing a small traveling
block, fitted with two fingers as shown in Fig. 62. This shaft
is connected directly, or by means of a flexible shaft, to the
reduced-speed shaft of the steering motor; near each end of
the worm shaft is a platinum-tipped contact spring. At the
center is a short stiff spring provided with a contact screw on
each side.

The operation is as follows: The apparatus is so adjusted
that the central position of the traveling block corresponds to
the central position of the rudder, and the end contact springs
are so placed that the operative leg of the motor circuit is
broken by the motion of the traveling block when the rudder
reaches the extreme right and left positions. The center-stop
contacts are engaged by the fingers on the traveling block a
short time before the rudder reaches the central position.
By closing the circuit of the electromagnet which operates the
rotary switch, these contacts make electrical connections which
effect the turning of the drum to the neutral position, and
thus stop the motor. The adjustment must be very care-
fully made in order to make the rudder stop at the exact
position corresponding to straight-ahead motion of the
boat.

Suppose the boat is steering ahead. An operator at the
control station desiring to take control depresses his key once,
the necessary length of the impulse transmitted being from
one-half to one second. This impulse will move the drum to
either a port or starboard position, and is sent in order to get
his bearings. Let us assume that the boat immediately begins
to swing to starboard. The steering motor has been energized
and is swinging the rudder to the right. The time required
for the rudder to move from the center to either extreme posi-

Il8 RADIODYNAMICS

tion is from five to fifteen seconds, depending on the speed of
the steering motor. This time could be fixed at any value
within these limits by adjustment of the field weakening
rheostat connected in series with the motor^s shunt field.

The operator, then, could allow the rudder to continue its
motion to the extreme position, where it would be automati-
cally stopped by the cut-off mechanism, or it could be stopped
at any intermediate position, by sending another correctly-
timed impulse after the first. This second impulse would
simply turn the drum to the next neutral position and thus
stop the motor. If he allowed the rudder to go to the extreme
position the boat would travel in its circle of minimum
diameter until the correct number of impulses were sent to
change the rudder's position.

Since the drum was revolved to a starboard position by the
first impulse, it remains there, the motor circuit for starboard
rotation being opened by the cut-off mechanism. Obviously,
then, two impulses are required to rotate the drum to the next
port position. If these are sent, the motor will rotate in the
opposite direction, and, if no more impulses are sent within
the fixed time limit, the rudder will move to the central posi-
tion and automatically stop. This central stop, as before
explained, is effected by the automatic rotation of the drum
to a neutral position. Remembering, then, that in this case
the neutral position is followed by a starboard position, one
impulse will send the boat to starboard again and the minimum
number of impulses for port steering is three. If these are
transmitted, the rudder will turn to the extreme port, unless
stopped at some intermediate position, by sending an additional
impulse.

It is thus seen that the nucleus of the apparatus is simply a
wirelessly-operated switch, supplemented by auxiliary ap-
paratus, which automatically perform operations that would
be very difficult for the distant operator.

HAMMOND RADIO RESEARCH LABORATORY II9

In practice a difficulty developed which was only overcome
after considerable experimentation. It was found that, when
the rudder and traveling block were in their central positions,
and three impulses were sent at the maximum speed permitted
by the inertia of the various parts, the drum remained on the
undesired contact long enough to allow a considerable number
of revolutions of the steering motor in the direction opposite to
that desired. The following would be the result:

The first impulse would effect rotation in the wrong direc-
tion, the motion of the traveling block being great enough
to allow the contact finger to pass under the spring. The
second impulse would bring the next blank space into posi-
tion, stopping the block's motion; the third would effect the
desired rudder motion and the block would immediately begin
to move with the rudder in the desired direction*. After a few
revolutions, however, the center-stop finger would engage its
contacts, and as a result the motor would stop.

In this way it was found impossible to get the rudder
through the central position from one side to the other.
Tests without the automatic stop, however, clearly indicated
the futility of trying to dispose of it, — it being found im-
possible to steer a straight course because of the difficulty of
stopping the rudder at the exact point necessary for steering
directly ahead.

Attempts were made to surmoimt this difficulty by the
introduction of considerable inertia into the rotating parts
connected to the motor, so that in the brief interval of time
necessary in passing over undesired operative positions of the
rotary switch, the motor could not develop enough speed to
cause the above-mentioned difficulty. This was partially
satisfactory, but did not completely solve the problem.

The solution was finally found in a "time relay," especially
built for this purpose after our plans, in New York. This
instrument consists principally of an iron-clad solenoid with

I20

RADIODYNAMICS

a movable core, and an adjustable air dash pot. A plan view
of this relay is shown in Fig. 63.

When energized, the core is drawn up in a period of time that
can be easily varied, by adjustment of a thumbscrew, from a
fifth of a second to ten seconds. A set of heavy platinum con-
tacts is fixed on the core and an adjustable screw so that a local
circuit, carrying ten or fifteen amperes can be satisfactorily
opened and closed at the end of the "in'* stroke. A light
spring serves quickly to bring the core back to the normal
position after the solenoid is de-energized. This is facilitated

F/eM fhtme

Sof^nosd

Sack Spring Cctf

-nrWnrr©!

Dashfhf

<J I' ll B ^ B ^ - w^ — — ^-f

— -^ Coir

Fig. 63.

by a one-way valve which permits the expulsion of. the air in
the dash pot with but little retardation on the return stroke.
The solenoid windings were connected in parallel with the
electromagnet of the rotary switch, and the contacts were
connected in one leg of the battery circuit to the motor
armature. By this means the motor armature current could
not be exerted until a definite length of time had elapsed
after the impulse had been sent, and thus the undesired oper-
ative positions on the drum switch could be passed over
without difficulty. The time limit was usually set at about
one second. Another time relay of the same kind was used
for engine control. In this way short impulses of about one-

HAMMOND RADIO RESEARCH LABORATORY

121

half second duration were used for steering, and long im-
pulses of about ten seconds were used for starting or stopping
the engine. The engine control in these experiments was
effected by opening or closing the ignition circuit, the engine
being so adjusted that it would stop at the required point at
which the explosions occur. It was found possible to start
the engine in this way as long as an hour after it had been
stopped. This second time relay was also used for firing ex-

Rotary Switch Afagrret

Potent'io Sensitive Retau
Detector / ja ='

r^^^n^ T^^f T

'*-i ocfding Inductance
"1 '^'^. 'Tuning Capacity

Time Re/au .
for Engine Control (

To Engine
Clutch ' control

J Signal Liqhfs\
y.'' on Yara-aim^

Fig. 64.

plosive charges of powder placed on top of the boat's cabin.
The complete circuit is shown in Fig. 64.

During the sunmier and autumn of 191 2, with this im-
proved apparatus, the results were very encouraging. The
25-knot Radio of which Fig. 65 is a reproduction was con-
trolled with reliability and precision at ranges of over three
miles, a distance far in excess of that attained by European
investigators. Demonstrations made before the U. S. War
Department authorities proved beyond a doubt that the
dirigible torpedo would be of great use in naval warfare,
especially for coast defense.

122

RADIODYNAMICS

The operations can be carried on at night almost as well as
by day. With a special reflector of the triple-mirror type,
and a searchlight, the maneuvers of the boat can be followed
with ease from the control point, although from any other
position the reflected light, and the boat itself, are practically
invisible.

The broad idea of the Hammond torpedo control system
for coast defense is this:

One powerful transmitting station is employed and suitably
placed in some protected situation with respect to the gunfire

Fig. 65.

of the enemy. A number of operators are placed along the
shore; these different operators have wire connection with
the wireless station and telephone connection with one
another. A number of torpedoes may be used, each of which is
controlled by an impulse of specific characteristics. These
are moored at a central protected torpedo base, and one or
more can be controlled at the same time by either of the
operators at the hidden control stations. The torpedoes are
started at the base and passed on to the control of the oper-
ators in the most advantageous positions, who operate under
orders transmitted over the telephone lines by the military

HAMMOND RADIO RESEARCH LABORATORY 1 23

head of the fortifications. The wireless station is equipped
with a wave generator for each torpedo, and by means of the
wire connections, which extend from the control point to
the central station, impulses can be sent from either of these
generators by either of the control operators.

CHAPTER XV

THE SOLUTION OF THE PROBLEMS RELATED TO
BATTLE-RANGE TORPEDO CONTROL

The problem of performing a number of operations aboard
a moving vessel at distances of oVer a mile is by no means a

I20r-

100

< 60

Galena,

^itOES^rlOM

^ » liOOm.

\500'^-,

Receive R

TRAN9HirT£R

. I I I

HWA.'/OAmos.

I I

Pistance- tnfensitij received current

on "D/fn^/A" w/th Solid' Rectifier- Detectotz.

20 30

MINUTES

Fig. 66.

simple one, even from a theoretical point of view. It might
be mentioned that controlling a number of mechanisms with
but a single relay is easy in comparison with wirelessly con-

124

BATTLE-RANGE TORPEDO CONTROL

125

trolling a relay five miles away, which at the same time is
immune from accidental or intentional interference from
other sources of energy. Then, too, when we reflect that
probably less than one-billionth of the energy radiated into
space by the transmitter reaches the receiver, the quanti-
tative aspects of the problem begin to come into evidence.

Fig. 66 is a graphical representation of the current re-
ceived on board the Pioneer ^ which was first used as a torpedo
in the Gloucester experiments. The transmitting energy in
the antenna * was about two kilowatts at a wave length of
approximately 1300 meters. The group frequency was 1000
and, with the air cooled quenched spark gap, and loose in-
ductive coupling between the open and closed oscillatory
circuits, the decrement was
fairly low.

The receiving antenna as
shown in the illustration
of iht Pioneer was of the
inverted L type, 30 feet
high and with a 20-foot
flat top, the detector was fig. 67.

one of the solid rectifier

type, essentially a crystal of galena with a light spring
contact. It is shown in Fig. 67 and was designed by the
author. The current values given were read directly upon
a Weston microammeter. The readings were taken at five-
minute intervals, except in close proximity to the station,
and the distances corresponding to these intervals were
computed from the boat's speed and log readings. This
curve shows how quickly the received current drops down
within a mile, and how it remains almost constant after this
distance is well passed. The high value of the received cur-
rent within a short distance of the transmitter may be

* 300 ft. high, 400 ft. flat top.

126

RADIODYNAMICS

due to the augmentation of the Hertzian eflects by the purely
electrostatic effects, as evidenced by the curve made in the
experiments with an electrostatic telegraph (Fig. 20). The
received current at three miles was only about 3.10"^ amperes.
So far as we were able to learn there was no relay, possessing the
necessary mechanical and electrical stability, which was sensi-
tive enough to operate reliably on such a small amount of
energy. The most sensitive relay we could procure in the
United States and Europe, which was rugged enough to
operate reliably under the conditions of shock and vibration
aboard a small high-speed boat in a rough sea, required about
300.10"^ amperes. We had as high a transmitting antenna
as was practicable, the most efficient transmitting apparatus,
and the most sensitive receiving set obtainable, and yet the

breach between the available
and the required received cur-
rent, was so wide that it ap-
peared almost impossible to
bridge it. With a sender that
could deliver only one mi-
croampere at four miles, and a
receiving relay that required
300 microamperes for opera-
tion, the problem was a serious
and discouraging one.

The first step in the solu-
tion was in the improvement
of the sensitive relay. This was of the Weston pivoted galva-
nometer type, and is reproduced in Fig. 68 by the courtesy of
the Weston Electrical Instrument Company. The permanent
magnet was replaced by an electromagnet, which, by increasing
the field intensity, more than doubled the sensitiveness. Fig.
69 shows graphically the effect of variation in the field energiz-
ing current. Later the author replaced the delicate platinum

Fig. 68.

BATTLE-RANGE TORPEDO CONTROL

127

contacts by a single platinum point on the movable arm,
and an adjustable globule of mercury. This increased the
operating sensitiveness from twenty to thirty times, for only
an extremely small contact pressure was required to keep the
circuit closed under considerable vibration. These relay im-
provements therefore increased the receiver's sensitiveness
about fifty times.

100

t 60

3 60

I 40

^^._

Remode/led Wmsfon Gatvanomm
1 Relate 1 1

ter

' ' r

^■^- IW***^

3L_=-^

ll —

Ta]

'***^

V —

z 4 e

FIELD CURREliT AMPS.

Fig. 69.

Fig. 70 is a plan view of this improved sensitive relay.
T and Ti are terminals of electromagnet windings, W and
Wi, surrounding soft iron cores. When in operation T and
Ti are connected to a source of direct current. T2 and T3
are terminals of movable coil C, the pivots and mountings of
which are not shown. B is a light arm fixed to C. Terminal
T4 is connected to arm B. L is a non-oxidizable contact
piece fixed to B. M is the top of a column of mercury ex-
tending into and above the block H. The size of the globule

128

RADIODYNAMICS

M above H is adjustable by screw S. The distance of M
from L in its normal inoperative position may be varied by
the adjusting screw Si.

Ordinary instruments of this kind have permanent magnets,
but by the use of electromagnets and suitably shaped pole
pieces, a much more intense field, and consequently a greater
sensitiveness, could be secured.

Fig. 70.

When C is energized by current flowing in the right direc-
tion, arrri B carrying contact L will move toward M. L will
make contact with and move into M and establish a good
low-resistance connection in the local circuit connected to T4
and Ts- When C is de-energized, the spiral spring Q causes
B to return to the normal position. With a relay of this
description currents of a few niicroamperes could be relayed
under conditions of vibration which necessitated a current of
a hundred microamperes with the best of ordmary sensitive
relays of the solid contact type.

BATTLE-RANGE TORPEDO CONTROL

129

The next step in the solution of the control problem was
to discard the Lodge-Mnirhead coherer, and to adopt the
vacuum-tube rectifier, which was perfected in this country
by DeForest. This is about twice as sensitive as the best
solid or electrolytic rectifiers, and has the additional advantage
of being more stable, both electrically and mechanically.

2400

RecEivcn

: n>fet ffio D ftecfc ^

.1-

Distance- Intensify Received Current
on 'DtRiGiA"' witti'Totentio" Detector,

20 30 40 5b

MINUTES
12 3 4

Fig. 71.

In attempting to improve this detector, the writer dis-
covered a connection arrangement which made the detector
a true potential-operated device. The other existing forms
of vacuum detectors as well as the many forms of solid recti-
fiers, electrolytic, thermal, thermoelectric and other detectors
are practically all conceded to be current operated, and be-
cause of this fact they not only consume energy, but also

130 RADIODYNAMICS

decrease the receiver's selectivity by increasing the damping
of the receiving circuits. This change in the receiving circuit
made the instrument approximately twenty-five times as sensi-
tive for relay or indicating instrimient operation; this ca*n
be readily observed from a comparison of* Fig. 71 with Fig. 66.
Both curves were made on the same trip, one going out to
sea and the other returning, in order to insure the greatest
possible similarity in the conditions. The transmitting energy
was also kept constant, the only variable factor being the
distance.

To prove that this circuit arrangement made the detector
a potential operated device, four of these detector circuits, each
with its separate indicating instriiment, were arranged so that
they could be simultaneously in connection with an antenna
circuit tuned to distant signals. It was found that in no case
was the signal intensity in the first set decreased by connect-
ing on one or all of the other three. Moreover the signals
in all four receivers were approximately equal. The sUght
inequalities were due to difference in sensitiveness of the
separate detectors. The effect on a single indicator could be
proportionally increased by connecting it to the secondary
winding of a transformer, having separate primaries which
were connected to the separate detectors. Theoretically this
circuit furnishes a means of securing any received current
desired, simply by connecting a sufficient number of units.

With these circuits the vacuum detector can be adjusted so
that the paralyzing effect of strong signals is not encountered.
This makes the detector electrically stable and is a very im-
portant feature. The detector can also be adjusted so that the
local battery current, which we shall call the field current,
increases or decreases as desired, when the signals arrive. We
will not attempt to give a theoretical consideration of the
detector's action, but simply explain the various circuits
employed.

BATTLE-RANGE TORPEDO CONTROL

131

TT,

Fig. 72 represents a vacuum tube detector, comprising ex-
hausted glass bulb H, in which are fixed iBlament W, grid G,
and plate F, the terminals of which are
T, Ti, T2, and T3. These terminals lead
through H in the usual manner. Fi, Gi,
and Wi, show more clearly the shapes and
relative sizes of the plate, grid, and filament,
respectively.

Fig. 73 is a diagrammatic representation of
the author's circuit arrangement for use with
the instnmaent shown in Fig. 72. When used in a circuit, such
as that shown in Fig. 72, this vacuum tube is called a Poten-
tio detector. That part of the diagram included in the circle
J is the Potentio detector circuit, and the remainder is

simply one of the large number
of ways in which it may be ap-
plied in a radio receiving set.

W is the hot wire filament,
which is maintained at an in-
candescent temperature by the
battery Bi, the degree of incan-
descence being varied by resist-
ance R. G is the grid, and F
the plate or cold electrode, which
is connected through the indicating instrument I, such as a
telephone, to the positive pole of the battery B. This bat-
tery in practice consists of about thirty cells; it is connected
to W through the variable connecting means K. The grid
terminal T is connected to some point in the receiving circuit
where the highest potentials are developed by the incoming
waves.

In this receiving circuit A is the antenna, L the open cir-
cuit tuning and coupling inductance, C a variable tuning
condenser, and E the earth connection. This open receiving

Fig. 73.

132

RADIODYNAMICS

circuit is coupled to the closed resonant circuit comprising
inductance Li and condenser Ci.

Fig. 74 illustrates another type of receiving circuit employ-
ing the well-known Oudin resonator principle for increasing
the potentials.

Fig. 75 illustrates a circuit arrangement and apparatus
used in producing an indicated effect greater than can be
obtained with one detector. With ordinary current-operated
detectors only one can be used advantageously in a receiv-
ing circuit, since with a plurality of detectors requiring current
energy for their operation, the energy of the incoming waves is

Fig. 74.

Fig. 75.

divided between the detectors, and consequently no increase
in effect is obtainable. It is possible and advantageous, how-
ever, to connect a plurality of Potentio detectors to one
antenna circuit, or circuits coupled to a single antenna, in
order to obtain an indicated effect much greater than is
possible with- one Potentio or with other detectors.

In Fig. 75 the antenna A2, condenser C4, inductance L3,
and earth E form the open receiving circuit. To a point of
maximum potential, such as T5, is made a connection which
leads to the grid terminals T of a plurality of Potentio circuits
represented by O, Oi, and O2. O, Oi, and O2 are similar to
that part of Fig. 73 included in the line J, with the exception

BATTLE- RANGE TORPEDO CONTROL

133

that the primary windings P, Pi, and P2 are used with O,
Oi, and O2 respectively instead of the indicator represented
by I. D is the core of a transformer in which P, Pi, and P2
are the primaries acting conjointly on secondary S. The
latter as shown is connected to indicating instrimient Ii.
This obviously receives the effects of O, Oi, and O2 combined
when the receiving circuit A2, L5, C4, E2 is energized by
received currents.

Fig. 76 is the cascade circuit for amplification. In this cir-
cuit arrangement the received energy develops potentials in L6

Fig. 76.

LUA5

aUJ

^G. 77.

which so influence the Potentio detector O3 as to cause varia-
tions in the battery current flowing through P3. The varia-
tions of current in P3 induce corresponding variations in the
secondary winding Si. These are of higher potential and in
turn effect the induction of currents of still higher potential
in S2. The final effects at the indicator I2 are thus increased
considerably over the initial effects.

Fig. 77 represents an adaptation of the Potentio circuit
which has been found especially valuable for the operation
of indicators of the galvanometer type. Experimental results
prove it to give indicated effects on galvanometers 25 times
as great as those obtainable under similar conditions with
solid rectifiers and other well-known detectors of equal

134 RADIODYNAMICS

sensitiveness. No improvement, however, is noted in tele-
phone operation.

The antenna circuit comprising antenna A4, inductance
coil L8, condenser C6, and earth E4, is coupled to the coil L9
by means of L8. The condenser C7 must be connected
in the circuit as shown in order to secure the greatly in-
creased effect not noticeable with other detectors or circuit
arrangements.

In practice B3 and Ri are adjusted until the desired indi-
cation is secured at I3, care being taken that the applied
voltage at B3 is not too high. By experiment the adjust-
ment should be made so that a decrease in the normal current
occurs when the signal arrives. Then by varying the capacity
of C7 while signal impulses are arriving the indications at I3
may be made to remain during and after the actuating signal
has ceased. The length of this time of indication after the
signal has ceased can be increased or diminished by variation
of the capacity C7. With C7 short circuited or with the
connection to C7 broken the effects at I are very much less,
so that it can be readily understood that the presence of C7
between the cold electrode and the end of L9 not connected
to Gi fulfills the condition necessary for obtaining the de-
sired operation.

There is no danger of burning out I3 by the action of ex-
cessively strong signals, since with signals above a certain
intensity value, the current in I3 will remain at zero. The
normal field current is diminished by the incoming signals in
proportion to the strength of these signals. This is another
important feature.

The Potentio detector stood up very well under the very
severe conditions. It must be remembered, as is shown by
the received current curve (Fig. 71), that the detector must
be rugged enough to remain in perfect adjustment under the
strongest signals received within a few hundred feet of the

BATTLE-RANGE TORPEDO CONTROL 135

transmitter, and at the same time it must be sensitive enough
to operate the relay at the extreme range of eight miles. It
must be capable of performing these functions for hours at a
time, perfectly, without a single hitch, or the necessity of
adjustment. The strongest signals in our experiments in-
variably caused the familiar "blue arc" between the plate
and filament, with the usual forms of connection with this
type of detector. This necessitates opening and reclosing of
the field battery circuit to restore the normal condition of
sensitiveness.

With the Potentio this is impossible. The blue arc is
caused by too great a density in the ionic field current. There
is a critical value which varies for different bulbs depending
on the degree of exhaustion and the distances between the
plate and filament. It is only necessary to bring the field
current to the critical value either by increase in the field
battery voltage, or by superimposing the currents arising
from incoming signals upon the normal battery current
through the ionic field, to start the arc.

It is possible to obviate this trouble, but only at the ex-
pense of sensitiveness. The most sensitive adjustment is
obtained when the field current is just below the critical
point. If the incandescence of the filament or the voltage
of the field battery is reduced sufficiently, the normal field
current can be made so low that the strongest incoming
oscillations will not cause a sufficient superimposition of cur-
rent to bring its value up to the critical point. But the cost
of this freedom from arcing is a great reduction in sensitive-
ness.

The adjustment of the Potentio is such that the normal
field current is safely enough below the critical value to allow
for increases due to occasional vibrations of the plate and
filament, which reduce the distance between them, and yet
high enough to insure good sensitiveness. Instead of in-

136 RADIODYNAMICS

creasing the field current the received oscillations decrease
its value. The strongest signals, instead of causing the blue
arc, can only bring the field current down to zero from its
normal value. Thus it is seen that the signal effect of the
Potentio is a change in the normal current, — a change which
decreases its value away from instead of towards the critical
point; that instead of producing excessively strong indicator
operating currents with excessively strong signals, the
Potentio automatically prevents such an effect by ceasing to
furnish an increase in field current change when signals in-
crease above a certain critical value.

CHAPTER XVI

THE DIFFICULTIES ENCOUNTERED IN PROVIDING
PROTECTION FROM INTERFERENCE

The selectivity problem, which is by far the greatest of all
difficulties to be overcome in the successful evolution of a wire-
lessly controlled torpedo, is one of comparative difficulty,
depending upon the degree of non-interferability desired. A
selective receiver is like a safety vault. The operator at the
transmitter may be likened to the owner of a safe who alone
possesses the combination. No safes are absolutely burglar
proof, and their value depends principally on the length of
time required for a skilled cracksman to reach the inside.
Likewise no receivers are absolutely selective for the simple
reason that an operator bent on interfering can take observa-
tions and measurements on the signals sent out to the selec-
tive receiver (just as the burglar may watch the opening of
a safe by the owner), and adjust his own apparatus to emit
waves of exactly the same characteristics as those of the
transmitter designed or adjusted for the selective receiver's
operation. The burglar, instead of trying to learn the com-
bination, may use sheer force in reaching the inside of the
safe. In the same manner a hostile transmitting station can
perform the desired effect in the selective receiver, i.e., operate
the receiving indicator or relay, by the emission of very strong
signals so that forced oscillations are set up. This is known
as the "whip crack" effect, and it is believed that very few
receivers are immune from it.

The best wireless signaling sets, such as those used by the
U. S. Navy are considered very selective, and yet the inter-

137

138

RADIODYNAMICS

ference existent between them is very serious. Take, for ex-
ample: Washington (Fig. 78) is receiving a message from the
Eiffel tower station in Paris, which is sending at 3000 meters
wave length. It is easily possible for a station in California,

with an equal amount of
power, and at practically the
same distance, to make the
Paris message unintelligible
at Washington, simply by
sending signals at or within,
say, two or three per cent of
3000 meters wave length.

Again, some insignijBcant
station with little power
within a few miles of Wash-
ington, could make it practi-
cally impossible for them to
receive any messages at all
from distant stations by send-
ing out broadly tuned sig-
nals of high damping. These
highly damped, or untuned
signals, by the previously
mentioned whip crack effect, cause the receiving antennae
to vibrate in their own periods, and thereby produce a great
deal of interference.

To illustrate: Sing a clear, steady tone into a piano. The
string, which when struck emits that tone, will audibly
vibrate in resonance. Then shout loud and gruffly into the
same piano; practically every string will be set in vibration,
producing a dull roar. The first tone corresponds to the
signals sent out by a tuned transmitter; the second (noise)
to the whip crack signals emitted by an untuned trans-
mitter.

Fig. 78.

Towers of the U. S. Naval Station at

Arlington, Va.

PROTECTION FROM INTERFERENCE 139

Another comparison might serve to illustrate the degree of
selectivity necessary for torpedo control. We have three
persons A, B, and C. A and B are together at one place, and
C is, say, a mile away. The problem is to allow A to hear
what C says while B is shouting in his ear. Impossible, you
say? Yet the torpedo problem is practically an exact analogy.
We must be able to make the electromagnetic ear of the
torpedo hear our control impulses eight miles away while it

■

_2?<rf -Ji

1L/Xl L°^J«i«*^^^^^^^K

*■

Hh^H E^-

It. _

Fig. 79.
Transmitter of Telefunken 5 kw. set aboard U. S. S. South Carolina.

is at the very side of a battleship capable of almost deafening
it with the force of its own powerful signals.

It is true that we could sidetrack the real problem, and
simply use such a large amount of energy at our shore station,
that more energy could be delivered to the torpedo at eight
miles than the hostile battleship could deliver at a hundred
feet. This is possible because the amount of energy that can be
efficiently used aboard a modern battleship does not greatly
exceed 5 kw. Such a 5 kw. set is shown in Figs. 79 and 80.
This is due to the limited size of the antenna. A shore station,
with practically no limits on the size and height of its antenna,

I40

RADIODYNAMICS

can easily use loo kw. The shore station also has the advan-
tage of being able to direct its energy somewhat in the general
direction of operations. This can be accomplished either by
the use of an inverted L-type antenna, with a flat top long in
proportion to its height, as suggested by Marconi, or by
means of the Bellini-Tosi Radiogoniometer.

Fig. 8o.
Receiving set aboard U. S. S. South Carolina.

Sidetracking the real problem by using a land station of
tremendous power is, however, not the practical and efficient
solution. In the first place, although desirable, absolute
selectivity is not necessary. A receiver that will require, say,
fifteen minutes time for the enemy to learn its combination,
will, in all probablity, satisfy the requirements.

We have described the systems used by the principal in-
vestigators abroad; those who have observed closely will
have seen at once that not one of these systems is immune to
intentional interference for the simple reason that no pro-
vision is made for avoiding the broadly tuned or whipcrack
signals, that may be sent out by any transmitter.

PROTECTION FROM INTERFERENCE 141

What use, we may then ask, and well, are the various types
of codal selectors and protective devices, when any hostile
battleship can absolutely lock the receiving apparatus so
that not even the controlling operator can get in a signal,
by the simple process known to operators as "sitting on the
key."

Systems like those of Anders Bull, Walter, Branley, and
others, providing complicated apparatus, aside from not being
able to cope with interference, actually defeat their own end
by their very presence; designed to increase the reliability of
operation, they diminish it by increasing the number of
mechanisms, especially those electrically operated, which are
likely to get out of order.

The keynote of success in developing mechanisms that must
operate without adjustment is simplicity. The simplest form
of distributor that will accomplish the end in view, namely,
to close any one of a nimiber of circuits, is all that is neces-
sary and indeed is to be greatly preferred. Wirth's ap-
paratus which provides means of changing the receiver's
wave length, is somewhat nearer the solution, but it, like
the others, provides no means of getting away from forced
oscillation effects; any system that does not do this is useless
for torpedo control.

The selectivity problem cannot be solved by any form of
cOdal selector or protective device inserted in the receiving
circuits after the relay; they must be placed before the relay,
that is, they must protect it from interference if they are to
serve their purpose. Instruments like the resonance relays
and monotelephone amplifiers have this protection inherently
by virtue of their vibratory elements tuned to the spark
frequency of the transmitter, but these, as pointed out else-
where, are subject to vibration, shocks, and sounds.

In order to reach the solution we must devise systems that
not only have a high degree of selectivity for tuned signals,

142

RADIODYNAMICS

but also provide means of evading the whip crack eflfects of
broadly tuned or plain-aerial transmitters.

Interference preventers have been invented, which, to a
large extent, prevent disturbances from untuned transmitters
of whip crack signals. At Washington, in 1910, the writer
witnessed government tests of such a receiver, worked out by
Fessenden. Reception of signals from
a station about 400 miles away, at
Brant Rock, Mass., was carried on
while a five-kilowatt station less than
a mile away was sending interfering
signals. The wave lengths of the two
transmitters were different by only a
few per cent. Fig. 81 is a diagram of
this receiver. The relation between
the two sets of coils is such that when
the same current passes through the
two primaries, no current is induced
in the secondary circuit, the ' two
secondary inductances, Li and L2
being wound in opposition. By tuning each circuit separately
to the incoming signals, and then throwing one of them slightly
out of tune, the broadly tuned and whip crack signals will
divide equally between the two primaries, while the tuned
signals will be received by one side alone, their strength un-
diminished by the presence of the other circuit to groxmd.

When such a receiver is used in conjunction with a trans-
mitter of the undamped, continuous wave type, like the high
frequency alternator, or the Duddell-Thompson arc, a very
considerable degree of freedom from interference is possible
for acoustic signaling.

Whether such a system is selective enough for torpedo
control depends upon the efifectiveness of two possible methods
of producing interference. One is, to listen for the controlling

Fig. 81.

PROTECTION FROM INTERFERENCE 143

impulses, measure their wave length, and then adjust their
own transmitter to send out similar signals. Whether or not
they can do this in the time necessary for the torpedo to reach
them (probably ten minutes), is not known. Since probably
not more than twenty-five short course-correcting impulses are
necessary to guide the torpedo to a target to a distance of, say,
six miles, it is a matter of conjecture. The other interference
method is to use one of the siren interference machines in-
vented in Germany. It consists essentially of a set of rotat-
ing switches, which automatically, and in rapid succession,
cause a series of sharply tuned waves of gradually increasing
length to be emitted. This, however, as an interference de-
vice, has the disadvantage that the available power is divided
among the different wave lengths used.

Assume that the energy is 5 kw., and that we use 20 sepa-
rate wave lengths. The energy on each wave length (not
taking into consideration the difference in efficiency with
change in wave length) is one-twentieth of the total or one-
fourth kilowatt. For telephone operation this would not
apply, since that instrument would give the full indication
during the short time that the particular wave length affect-
ing it was being emitted, and thus make reception of other
signals impossible; but for relay operation unless the separate
wave lengths were each emitted for a time equal to the me-
chanical vibration period of the relay's movable element, or
longer, the effect would be equivalent to the effect of a one-
fourth kilowatt transmitter in continuous operation on the
correct wave length. Even though the rotating switches
were rotated at a speed slow enough to cause a closure of the
relay each time the correct wave length was emitted, the
fact that nineteen other similar wave lengths must be sent
out in succession, each for the same length of time, makes
the interfering impulses so far between that corrections can
be made from the control station.

144 RADIODYNAMICS

The second method, even with the limitations explained,
is probably the better of the two methods, as the shore station
could send out confusing or blind signals differing in wave
length from the steering impulses, so that the enemy afloat
would have no means of. determining which was actually the
correct one.

In order to increase the selectivity of torpedo operation to
such a point where interference is much more impractical,
Mr. Hammond and the writer worked out a number of Selec-
tive control systems. Of these only a few will be described.
Since the work done along this line at the Hammond Radio
Research Laboratory is practically the only work of this
kind in the United States, and since nothing new is forthcom-
ing from European inventors, these selective systems repre-
sent the latest improvement along this line.

CHAPTER XVn

A MEANS OF OBTAINING SELECTIVITY

Selective Transmitter-Receiver Unit. — Fig. 82 illustrates a
type of transmitter-receiver unit suggested by the writer in
191 1. H.F.A. is a high-frequency alternator, or other high-
frequency current producer, which supplies energy to Li
through interrupters Ii, I2, and key K.

The principle applied in this selectivity scheme is the same
as that brought forward by Blondel in his spark-tuned re-

HFi

LsU

5 7f^, R'l gp lip Y

c»

Fig. 82.

ceiver some time ago, but it has the additional selectivity of
one or more other circuits, besides the high-frequency and
spark-tuned circuits. Moreover, this other circuit, which is
tuned to an intermediate frequency between the two men-
tioned at the transmitter, has an inaudible periodicity, so
that the signals cannot be heard at all by an ordinary re-
ceiver. The wave length of this inaudible frequency is so
far above the wave lengths used in signaling that the ordi-
nary receiving circuits will not respond to it, and so far below
that of the spark-tuned circuits that they would give no indi-
cation even if the frequency were audible.

14s

146

RADIODYNAMICS

Supposing the stiffness of the receiving circuits is such as
to require twenty impressed oscillations to swing them up to
full amplitude, then the ratio of the different frequencies at
the transmitter should be 20 to i, that is, the transmitter
emits several frequencies, all in the same wave, the values
of which drop down in steps according to the ratio 20 to i or
the ratio found most suitable.

Consider the wave length of the emitted waves to be 1000
meters. The oscillation frequency corresponding to that
value is 300,000 per second. The oscillation frequency at
H.F.A. would then be 300,000. Allowing 20 oscillations to

UJ.

KFA. L

Sir i liio2> ...

ilcr^

Fig. 83.

Fig. 84.

the wave train, the interrupter Ii would have a. frequency of
15,000 per second. That is, at each contact of Ii, 20 com-
plete oscillations from H.F.A. would occur in Li and be
radiated from A. Dividing 15,000 by 20 we have 750, the
frequency of interrupter I2. When key K is closed antenna
A then radiates electric waves of 1000 meters length, which
are broken up into an inaudible group frequency by Ii. This
resultant signal is then broken up into a frequency of a lower
order, determined by the speed of I2.

Figs. 83 and 84 show two other ways of obtaining the same
results as with Fig. 82. In Fig. 83 G is an alternating-current
generator having a periodicity of about 7500 cycles, which
excites the field windings of high-frequency alternator H.F.A.,

A MEANS OF OBTAINING SELECTIVITY 147

the latter being rotated at such, speed as to give a 300,000-
cycle current. Th6 current delivered by H.F.A. will then
have a periodic amplitude variation of a frequency correspond-
ing to G, namely 15,000. H.F.A. delivers this periodically
varying 300,000-cycle current through interrupter I and key
K, to antenna A by means of the inductively coupled coils,
Li and L2.

When interrupter I is stationary or short circuited, an-
tenna A radiates electric waves of 1000 meters length at an
amplitude frequency of 15,000, which being above the audible
limit, will not be heard by a spark receiving set. If I is
rotating so as to give 750 contacts per second, A will radiate
this wave of two periodic characteristics at a rate of 750 per
second, which of course is audible. Thus in Fig. 83 G takes
the place of Ii, in Fig. 82, for producing the 15,000 per second
group frequency.

Fig. 84 shows another method of producing a high-fre-
quency current having two or more group frequencies within
or out of the range of audibility. B is an arc oscillatory-cur-
rent generator of the Duddell-Thompson type, fed from a
source of direct current. In shunt around the arc is a con-
denser, Ci, inductance, L2, and interrupter, I.

Consider I as being short circuited and circuit B-C-Li
open, then as is well known in the art, when B, Ci, and L2
are properly adjusted, oscillatory currents will be generated
in the circuit B-C1-L2, the frequency of the alternating
currents developed being dependent principally on the values
of Ci and L2. Now if circuit B-C-Li be closed oscillations
will be generated in it of, say, 7500 cycles. This has the
eflfect of producing a 7500 cycle amplitude variation of the
current of the circuit B~Ci-L2 and antenna A being in
resonance with B~Ci-L2, will radiate electric waves of
300,000 oscillatory frequency, and at a group frequency of
15,000 impulses per second.

148

RADIODYNAMICS

Now if interrupter I, giving 750 contacts per second, be
included in the circuit B-C1-L2, the radiated waves will be
broken up into the audible frequency of 750 per second.

The receiving circuits, as shown in Fig. 82, are tuned to the
oscillatory current frequency, the inaudible amplitude fre-
quency, and the audible group frequency. Antenna circuit
A2-L3-C and circuit L4-C1 are both tuned to the trans-
mitter oscillation frequency. By the action of rectifier Ri,
Ls receives unidirectional currents from L4-C1, thereby
energizing circuit L6-L7-C2, which is in resonance with the
frequency produced by the interrupter giving 15,000 contacts

LUs 5LLJ

■d-

-Nt

Mp pisQw

Fig. 85.

Fig. 2>6.

per second. If I2 of Fig. 82 is in operation, circuit L8-C3-P
will then be energized, and telegraphic signals may be pro-
duced at P by the transmitting key K.

Figs. 85 and 86 show two other methods of producing the
ultra audible group frequencies of the high-frequency currents.
In Fig. 85, I is a high-frequeiicy alternator supplying current
to antenna 6 through interrupter 3 and key 2, and coupling
coils 4 and 5. Motor 7 is mechanically connected to coil 5
and rotates it in such a way as to produce a periodic ampli-
tude variation, the frequency of which is ultra-audible.

In Fig. 86, antenna 8 is inductively connected to high-
frequency alternator 12 and ultra-audible frequency alter-

A MEANS OF OBTAINING SELECTIVITY 149

nator 16 by means of coupling coils 9 and 10, and 14 and 15
respectively. An interrupter 11 and key 13 are in circuit
with 12.

When the transmitter is in operation, 11 interrupts the
current from 12 at an audible rate, and by the action of 16,
the amplitude of the antenna current is varied periodically,
the periodicity being dependent upon the frequency of 16.

CHAPTER XVm

NATURE OF INDICATOR CURRENTS IN RADIO
RECEIVERS

The absolute necessity for a simple and effective inter-
ference preventer for our torpedo control system led the
author, in the fall of 191 2, to investigate the nature of the
phenomenon accompanying the reception and indication of
alternating-current waves of radio lengths.

Prof. G. W. Pierce, of Harvard University, has already
done considerable work along this line, and in his bodi on

the ** Principles of Wireless Telegraphy '* are found the

results of his extensive researches on detectors and

rectification phenomena, together with hypotheses

:r7) based on them. Although Professor Pierce's work has

been mainly along the line of determining the cause of

rectification in radio detectors, he also presents brief

but concise discussions on the nature of the received
Fig. 87.

currents in the indicator circuit.

On pages 173-174, explaining the action of solid rectifiers
in a receiving circuit like that shown in Fig. 87, he says:

**A train of incoming waves produces an alternating e.m.f.
in the antenna circuit. This e.m.f., when in one direction,
produces a large current through the detector, charging the
antenna. When the e.m.f. reverses the current from the
antenna to the ground through the carborundum is smaller,
thus leaving the antenna charged with a small quantity of
electricity. The effect of the whole train of waves is addi-
tive, so that this charge on the antenna is cumulative. The
accumulated charge on the antenna escapes through the

ISO

NATURE OF INDICATOR CURRENTS 151

telephone shunted about the carborundum, causing the dia-
phragm to move. Each subsequent train of waves causes a
similar motion of the diaphragm, which is evidenced as a note
in the telephone, equal in pitch with the train frequency of
the waves.

'*It is immaterial whether the detector permits the larger
current to flow upward, charging the antenna positively, or
permits the larger current to flow in the downward direction,
charging the antenna negatively. The explanation is the
same in both cases.

'*With very slight change this explanation can be made to
apply also to those cases in which the detector is in a con-
denser circuit coupled inductively or directly with the antenna
circuit."

Such a modification consists essentially in substituting the
stopping condenser for the capacity, and the coupling coil
for the inductance of the antenna. That the two
circuits are of the same type is seen by an inspec-
tion of Figs. 87 and 88. In both cases the detector
has the alternating e.m.f. impressed upon it and,
as Dr. Pierce told the author personally, the
charge accumulates, in the stopping condenser,
and discharges through the indicator at a rate ^^^ gg
equal to the transmitter's group frequency, and
in exactly the same manner as in the previously mentioned
circuit.

The best value for the stopping capacity, if this be true,
would be such that with signals of medium intensity, it would
be completely charged by one wave train. The resistance of
the receiving telephone also influences their best value, and
must be taken into consideration.

The application of such an explanation to relay operation
is, however, of principal interest to us. There is no reason
why the theory applied to arriving wave trains of 1000 per

152 RADIODYNAMICS

second frequency should not hold equally well for trains of
much greater length, provided the stopping condenser is
large enough to absorb all the energy delivered by the rectifier
during that longer train. Neither is there any reason ap-
parent why wave trains composed of equal amplitude oscilla-
tions should not act in the same way as do the damped trains.

Granting these suppositions, we coidd use undamped oscil-
lations in trains of any length, and a stopping condenser
sufficiently large to absorb all the energy supplied to it during
that time by the detector. At the end of the wave train then
the accimiulated charge in the condenser woidd discharge
through the relay with much greater effect than could be
obtained with short successive wave trains. Experiments
based on these suppositions were performed, but no increased
relay deflections could be obtained.

In a sketch of the action of wireless telephonic apparatus,
on page 305 of his book, Dr. Pierce says:

"The receiving apparatus is identical with that employed
in wireless telegraphy, and makes use of a receiving antenna
coupled with a circuit containing some type of rectifying
detector; e.g., an electrolytic detector, a crystal contact de-
tector, or a vacuum tube rectifier. About the detector is
shunted a sensitive telephone receiver.

"The action is as follows: If an unmodified train of electric
waves having a frequency higher than the limit of himaan
audibility (35,000 vibrations per second) arrives at the re-
ceiving station, the receiving circuit, if properly tuned, will
sustain electric oscillations which, passing through the de-
tector, will be rectified and will give a series of rectified im-
pulses to the receiving telephone circuit.

"These impulses, being all in one direction, will act as a
continuous pull on the diaphragm, — a continuous pull for
the reason that the diaphragm cannot follow the rapid suc-
cessive impulses, and because also, on account of the inductance

NATURE OF INDICATOR CURRENTS 1$$

of the telephone circuit these impulses are modified electrically
into practically continuous current through the receiver,'^

An application of this explanation for a receiver which
discriminates between spark and undamped wave signals
for relay operation at once suggests itself. If the inductance
of the telephone or relay is high enough to smooth the high-
frequency direct-current impulses into a practically con-
tinuous current, the indicator current, then, with unbroken,
undamped oscillations, is practically unvarying and uni-
directional. For spark signals or chopped continuous wave
signals of audible frequencies, the high-frequency direct-
current impulses are modified into one impulse the length of
the train, but the self-inductance of the indicator is insufficient
to appreciably affect these longer train-length impulses, so
that they pass through unmodified. However, by inserting
a choke coil of large value, the broken signals may be greatly
reduced in intensity, while the unbroken signals remain
practically the same as before, except for a decrease in ampli-
tude due to the added ohmic resistance of the choke coil. A
selective receiver based on this principle will be described in
a subsequent chapter.

That these two explanations do not agree is evident, but
it is difficult to understand why the action for continuous
waves should be other than the action for damped trains of
waves.

In November of 191 2 the writer performed some experi-
ments in the effort to verify either of Piercers theories, or to
unearth the true explanation of the nature of the received
current in the indicator circuit. These experiments, although
crude and incomplete seem to shed new light upon this little
investigated phenomenon.

The writer presents the data and conclusions derived from
these tests in the hope that they may incite further investi-
gation.

154

RADIODYNAMICS

Experimental Determination of the Nature of the Indicator-
operating. Currents in a Radio Receiver

Fig. 89 shows diagrammatically the connections and
arrangement of apparatus, and the following table gives data
relative to the apparatus used.

,-=r^m

^n!L

p s

Jf^

7 VI

~ K Ffi M

IMJ

Fig. 89.

B Storage battery.

E Ericcson test buzzer.

K Key.

V Murdock variable condenser (max. cap. 0.002 mfd.) set at 100°

Vi Murdock variable condenser (naax. cap. 0.002 mfd.) set at 120°

V2 Murdock variable condenser (max. cap. 0.002 mfd.) set at 45°

V3. Murdock variable condenser (max. cap. 0.002 mfd.) set at 60°

V4 Murdock variable condenser (max. cap. 0.002 mfd.) set at 180°

P Primary Murdock inductive tuner 69 turns.

Pi Primary Murdock inductive timer 72 turns.

S Secondary Murdock inductive tuner, contact stud No. 2.

Si Secondary Murdock inductive tuner, contact stud No. 3.

D Iron pyrite detector.

Di Iron pyrite detector.

F 3000-ohm Schmidt- Wilkes telephone receiver.

R Weston relay (microammeter movement).

Fi 300-ohm Marconi wavemeter phone.

L 2500-ohm, 8-c. p., carbon filament lamp. '

1 2500-ohm (d. c.) No. 34 copper wire coils (2) on a laminated wire

core.
H Distance of apparatus in circle from remainder, 10 feet.

Experiments and Observations

With the apparatus arranged and adjusted as shown and
in operation, the following experiments and observations were
made:

NATURE OF INDICATOR CURRENTS 155

1. Test for timing: With the coupling between the coils of
the two tuners moderately weak (secondaries about three-
fourths the way out of primaries), the tuning was fairly
sharp, the point of maximum signal intensity being capable
of determination to within i or 2 degrees on either of the
variable tuning condensers, V, Vi, or V3.

2. To prove that tertiary circuit, S1-V3, does not receive
its energy direct from primary exciting circuit, V-P, instead
of from the rectifier D, as intended: Signals in F were di-
minished to inaudibility by variation of Vi.

3. Test for difference in energy between secondary (S-Vi),
and tertiary (S1-V3) circuits: F connected across D, with
Pi disconnected, indicated a signal that was only slightly
greater than at Di.

4. With D elements out of contact, it was found necessary
to change Vi to 60 degrees for resonance, but signals at F
were very sharply tuned and much stronger.

5. R, Fi, L, and I were separately thrown in circuit with
D and Pi with the following results at F, the signal inten-
sities being in the order given.

I O.

2 R.

3 ...Fi

4.. L.

5 1. Signals very weak.

No great difference between the intensities;
signals moderately strong.

6. All apparatus included by circle H was replaced by a
closely coupled set of coils on a laminated core, a variable

Fig. 90.

]

condenser, and a telephone, all compris- -.. — ^ . -rifl-

ing a low-frequency oscillatory circuit of

such wave length as to respond to the

group frequency of the buzzer signals.

(See Fig. 90.) The signals at F2 were considerably reduced

with this arrangement, but fairly good spark timing coidd be

secured.

IS6 RADIODYNAMICS

7. Change of detectors at D: Detectors of various types,
such as the different forms of the vacumn tube rectifier,
carborundum, and electrolytic, were used at D with practi-
cally no change in results, save that in some instances the
signals through the whole series of tests were stronger or
weaker due to differences in detector sensitiveness.

Conclusions Drawn from Tests

The very fact that energy in the form of timed high-fre-
quency oscillatory currents is developed in the tertiary
circuit is a proof that the effect of a train of waves is not ad-
ditive; that the whole train of waves does not pass through
the indicator as a single pulse in one direction, but that each
separate impulse in the train passes through the indicator
without losing its distinctness, and is not smoothed down into
one impulse with the others in the train. The fact that this
tertiary circuit was 10 feet distant from the other circuits,
and the fact that when the audions were used as detectors,
the signals at F could be cut out completely by de-energizing
the filament, show conclusively that the currents in the
tertiary circuit were not set up by direct induction from the
primary exciting circuit, and that therefore they were due to
the "blow excitation" of the distinct high-frequency direct-
current impulses arriving from D, the rectifier. The fact
that there was timing, and that the selectivity was so good
that the signals at F could be rendered inaudible by varia-
tion of Vi, also strongly support this proof.

The fact that the signals at F were very nearly as strong
as when F was connected across D, indicates that the rectified
high-frequency impulses were not flattened greatly, due to
inductive resistance, as otherwise the energy delivered by
Di to F could not have been so great, and the tuning would
not have been so good.

With D out of contact the result was simply to connect V2

NATURE OF INDICATOR CURRENTS 157

in parallel with Vi, Pi being in this connecting line, the wave
length being thereby increased so that it, was necessary to
decrease Vi to 60 degrees in order to restore resonance con-
ditions; the current in Pi was therefore alternating instead
of pulsating direct, and maximum value instead of half value,
due to the chopping off action of the rectifier. The signals
at F were, therefore, much stronger.

The fact that there was no very noticeable decrease in
signal intensity when N was changed successively from O to
R, F, and L, apparently indicates two things, namely: (i) the
resistance of the detector D was very high, for additional
resistances up to 2500 ohms in its circuit with P did not
greatly change the total resistance of the circuit, since by
their addition the signals were not greatly diminished; and
(2), coils of wire wound on magnetized or j)ermanent magnet
cores present little inductive resistance to high-frequency
pulsating currents. (The coil of the Weston relay R sur-
rounds a core magnetized by the j)ermanent magnet of the
instrument; the coils of the Marconi phone, Fi, are wound
on permanent magnet poles.)

When I, the coils of copper wire inductively woimd on a
laminated core, having a resistance equal to that of the lamp^
L, was connected, the signals became very nearly inaudible.
This shows that inductances with soft, laminated iron cores
present a relatively high inductive resistance to high-frequency
pulsating currents. Since these coils had considerable dis-
tributed capacity it is believed the weak signals that were
heard were due to the conductive effects of this capacity.

The intensity of the signals was decreased to this great
extent, because the high-inductive resistance of I obliterated
the separate pulses in the train, and lumped them into one
imidirectional-current impulse the length of the train, which,
having a very low frequency, could not swing up circuit
Si-V into resonant operation; the detector Di and tele-

158 RADIODYNAMICS

phone F, therefore received no energy, and so no signals were
heard.

That this lumping action does occur was shown with
the low-frequency tuned circuit, which responded to the
group frequency of these impulses. The reduction in in-
tensity of the received current at F2 in this low-frequency
circuit was due to the fact that with the apparatus at hand,
a high resistance was inevitable in order to secure the in-
ductance necessary for obtaining the long wave length re-
quired in that circuit.

The tests with different detectors show that all give prac-
tically the same effects.

CHAPTER XrX
THE INTERFERENCE PREVENTER

The writer devised this receiver in order to utilize fun-
damental principles relating to the flow of direct and
alternating currents for the production of a highly selective
radio system.

These properties have been applied in wire telephony, and
kindred branches of the electrical arts, and, more specifically,
deal with electrical circuits and their properties. These
properties may be so varied as to make the circuit conductive
to currents of constant value, while greatly resisting the flow
of varying currents, and vice versa. In other words, by in-
serting an electrostatic condenser in a metallic circuit con-
nected to a source of alternating potentials, an alternating
current would flow, but the same circuit would present an
infinitely high resistance to the flow of a direct current.
Also by inserting a coil of high self-inductance in a metallic
circuit connected to a source of direct imvarying currents,
the resistance to direct currents would be low, while the same
circuit would greatly impede the flow of an alternating or
varying current, the extent of the impedance depending upon
the inductance of the coil, the limits between which the
amplitude of the current varies, and the frequency of the
alternations or variations.

In radio signaling systems of today two principal kinds of
electric wave producers are in general use. The older of
these is the spark system, with which electromagnetic waves
are generated by the spark discharge of a condenser. The
waves are sent out in groups, the group frequency being de-

159

l6o RADIODYNAMICS

j)endent upon the frequency of the alternating current charg-
ing the condenser, and the spark-gap setting, and the length
of the waves upon the electrical sizes of the condenser, and
the inductance through which it discharges.

The number of waves in a train is governed by the damping
of the circuit, which, in turn, dej)ends on the various sources
of energy loss, such as heating, and radiation of electro-
magnetic waves.

For example, take a 500-cycle transmitter emitting a 1000-
meter wave. The 500-cycle alternator is connected to the
condenser circuit through a step-up transformer. The con-
denser is charged during the first half of each alternation of
the primary current and discharges across the spark gap
when its potential reaches the necessary value. This dis-
charge occurs at the j)eak of the alternating-current wave in
the primary circuit, is oscillatory in nature, and the number
of oscillations in the train is dependent upon the damping.
If the damping is small 15 oscillations may occur in the de-
cadent train before the potential drops too low to overcome
the resistance of the spark gap.

The time during which the discharge takes place, therefore,
with a looo-meter wave (300,000 frequency), and 15 com-
plete cycles to the train, would be ^ — of a second, or one

150,000

ten-thousandth of a second. Thus with the 500-cycle, 1000-
meter wave transmitter, once in each one-thousandth of a
second the condenser discharges for one ten-thousandth of a
second, producing a decadent train of, say, 15 oscillations.

The other type of transmitter is the continuous wave
generator, which either by the high-frequency alternator or
the Duddell-Thompson arc, produces continuous undamped
waves. The waves, instead of being produced in decadent
trains during only one-tenth of the time, as with the spark
sets, are generated continuously and with constant amplitude.

THE INTERFERENCE PREVENTER l6l

At the receiving station the effects produced by the two
types of wave generators is somewhat different.

With the spark set the oscillatory currents developed in
the receiving antennae by the transmitter, and built up by
resonance are rectified, and flow through the indicating in-
strument. The telephone, which is used as the indicating
instrument, therefore receives a direct-current impulse for
each discharge of the transmitting condenser. These im-
pulses, although consisting of a number of separate impulses,
act as one pidl on the telephone diaphragm, which vibrates
at a rate of looo times per second, corresponding to the trans-
mitting group frequency. This periodic motion produces an
acoustic note of high pitch. Dots and dashes are distinguished
by the length of time during which the note is produced,
dots, say, one-tenth second, and dashes one-fifth to one-half
second. This note is produced in the receiving telephone
only when the transmitting key is closed.

With the imdamped wave transmitter there is no audible
variation in the received rectified current, the effect of which
is practically the same as that of a continuous direct current
in the receiving telephone. Therefore a continuous pull on
the diaphragm results so long as the sending key is depressed.

This, then, is the essential difference, from a low-frequency
consideration, between the effects of spark transmitters and
undamped wave transmitters. The former produces a
periodic received current, while the latter produces a constant
received current.

At present radio stations using these different systems pro-
duce considerable mutual interference. By the use of suitable
apparatus we may differentiate between the two kinds of
effects at the receiving station, and thereby secure a greater
degree of selectivity. %

The following description covers methods for accomplishing
the desired results, with particular reference to the circuit

l62

RADIODYNAMICS

arrangements illustrated by the drawings. Figs. 91, 92 and
93 show graphically three common types of radio trans-
mitters.

Fig. 91 illustrates a spark transmitting set. The alter-
nating-current generator G supplies current to primary P
of step-up transformer T, through the controlling key K.
Secondary S supplies high potential current for charging
condenser C, to break down the spark gap SG. When the
potential reaches the sparking value, C discharges across SG,
and through inductance L, and by electromagnetic induction
and resonance, an oscillatory current is set up in the radiating
system composed of antenna A, inductance Li, and earth E.

Fig. 91.

Fig. 92.

In Fig. 92 a continuous wave transmitter is shown. High-
frequency alternator, H.F.A., sets antenna Ai into electrical
vibration by means of coupling coils L2 and L3, as is common
in the art. The antenna is earthed at E, and signals are sent
by making a condition of resonance or dissonance between
H.F.A. and the tuned radiating system A1-L3-E1. This is
accomplished by short-circuiting or otherwise changing the in-
ductance or capacity of the radiating system with the trans-
mitter key in such a manner as to produce the desired signal.
In this way the signals may consist either of periods of work
or of rest of the radiator.

Fig. 93 illustrates an undamped wave transmitter, based

THE INTERFERENCE PREVENTER

163

on the principles of the Duddell-Thompson oscillatory arc.
The direct-current generator Gi, which preferably gives a
potential of about 500 volts, supplies direct current to the
electrodes of the arc AR, through the choke coils L4 and L5.
When properly adjusted, electric oscillations are set up in the
closed oscillatory circuit, comprising arc AR, condenser Ci,
and inductance coil L6, the frequency of which is determined
principally by the values of Ci and L6. By electromagnetic
induction and resonance oscillatory currents are produced in
the radiating system composed of antenna A2, inductance
L7, and earth E2. In order to send signals, the key K2,
which establishes resonance, is used.

.UJ

£2

u \\\^ — maxam — s.

t^ II i nM i mm i* ^*"

L-8

Fig. 93.

Fig. 94.

Figs. 94, 95 and 96 are schematic representations of re-
ceivers based on the idea of reducing interference between
spark and undamped wave systems.

Fig. 94 illustrates the circuit arrangements of a receiver
for use with an undamped wave transmitter, such as Fig. 92
or 93.

The action is as follows: By the phenomenon of electric
wave propagation and reception, when the transmitting key
is closed, alternating currents of high frequency are de-
veloped in the resonant receiving antenna system, which in-
cludes antenna A3, inductance L8, condenser C2, and earth
E3. Circuit L9-C4-D is energized, and current energy is sup-

164 RADIODYNAMICS

plied to detector D, through the stopping condenser C4. D
is a detector such as a thermal or thermoelectric; Lio is a
choke coil, and I an indicating instrument for translating the
received currents into effects observable with one or more of
the physical senses. D produces a unidirectional current in
the circuit D-Lio-I, for each wave train impressed upon it.
That is, for signals from a 5oocycle spark transmitter, D
produces a pulsating, unidirectional current in the indicating
circuit, the frequency of which is 1000 per second, equal to
the transmitting group frequency, and for signals from an
imdamped-wave transmitter. D produces a luiidirectional,
imvarying current in the indicator circuit. Therefore it is
obvious that the distinguishing difference between spark and
imdamped-wave signals is that one produces a j)eriodic re-
ceived current, while the other produces a constant received
current. The detector D, it must be imderstood, has too
much inertia to follow the high-frequency impulses of the
oscillatory current, which are of the order of 500,000 per
second, but it can and does follow the impulses correspond-
ing to the group frequency, which need not be greater than
1000 per second. This inertia or lagging action is due to the
fact that detectors of this class which are operated by the
heat developed by the incoming oscillations, cannot heat and
cool with sufficient rapidity to follow the enormously high
number of periodic variations in the heat-producing current.

Referring now to Fig. 94, choke coil Lio is of such value
as to greatly impede the flow of the periodically varying cur-
rents produced by spark transmitters, while direct currents
set up by continuous wave transmitters flow imimpeded.
For this reason the interfering effect of a near-by spark station
on a continuous wave receiving station is greatly reduced.

Fig. 95 illustrates another method of securing the same
freedom from disturbance. The receiving antenna system,
composed of A4, Lii, Cs, and E4 is coupled to the closed

THE INTERFERENCE PREVENTER

165

oscillatory circuit, comprising L12 and C6, with which it
is in resonance. Circuit L12-C6 supplies osdllatory-current
energy to detector Di, which furnishes unidirectional current
to winding W of indicating the instrument and to primary

Lii

RJL

wB ^T.

M ^^^ Di

Fig. 95.

Pi of transformer Ti. Secondary
Si is connected to winding Wi
through stopping condenser C8, and
rectifier D2 rectifies the alternating
current supplied by Si for use at
Wi.

The indicating instrument is here
represented as a relay in which M
is the moving element, but any other
form of indicating instrument may be used, or W and Wi
may be independent primaries of an induction coil, both of
which, when in operation, produce equal and opposite effects
upon a secondary coil, connected to the indicating instru-
ment, while one, operating alone, produces the signal effect.

The operation is as follows: When continuous wave signals
are received, Di supplies unidirectional currents to W and
Pi. There is no induction of current into Si, because the
currents in Pi do not vary, and therefore only W of Ii is
energized, and M is attracted, i.e., the relay is operated.

If periodic currents are delivered by Di, such as are set
up by spark transmitters, currents are induced in Si and
therefore Wi receives direct-current impulses by the action
of D2 and C8. Now Ti, W, and Wi are so proportioned that
with spark signals of the common frequencies, the magnetic
effects of W and Wi are equal and opposite. M will, there-
fore, be unaffected when group-frequency signals are received,
but wiU operate without difficulty with continuous wave
signals.

Fig. 96 represents the circuit arrangements and apparatus
necessary to prevent interference from continuous wave

l66 RADIODYNAMICS

transmitters to receivers of spark signals, such as are pro-
duced by the transmitters of Fig. 91. Antenna A6, induc-
tance L16, condenser C12, and earth E6, form the receiving
antenna circuit. Coupled to this is the closed circuit com-
Uj posed of inductance L17 and ca-

pacity C13. The two circuits are
tuned to resonance with each other
^ '*-^* — and with the transmitter. When

d c — I7I I L Itt B" — 1 ana witn tne transmitter, wnen

* r Tjcm I ftfi_q^__T energized, L17-C13 suppues energy

c«^ to detector D4, through stopping

^ condenser C14. D4 delivers imi-

▼ directional currents to primary P2

Fig. 96. ^f transformer T2. Secondary S2

is connected to telephone F2. The continuous currents
produced in the circuit D4-P2 by continuous wave trans-
mitters produce no induced currents in S2. Therefore F2
does not operate when continuous wave signals are re-
ceived. Spark signals, however, produce periodic direct
currents in P2, which by induction produce alternating cur-
rents in S2 and F2. F2 therefore receives spark signals with-
out difficulty, but remains inoperative . ^ .
for continuous wave signals. fe i " i^i^g Ala

Fig. 97 is a schematic representation — — ' "^^"^^*
of a thermal detector circuit. D is the ^' ^^'

fine wire of the thermal detector, which is connected in series
with choke coil L18, indicating instrument I2, and a source
of direct current Z, which is a battery and potentiometer.

This circuit is suitable for use with the antenna circuit
shown in Fig, 94 for the continuous wave receiver.

CHAPTER XX
DETECTORS

According to the definition adopted by the standardization
committee of the Institute of Radio Engineers, a radio de-
tector is "that portion of the receiving apparatus which, con-
nected to a circuit carrying currents of radio frequency, and
in conjimction with a self-contained or separate indicator,
translates the radio-frequency energy into a form suitable for
the operation of the indicator. This translation may be
effected either by the conversion of the radio-frequency
energy, or by means of the control of local energy by the
energy received."

A wrong impression relative to the exact fimction of a de-
tector in a wireless receiver has been prevalent among those
engaged in radio work. This misconception, as pointed out
by Professor Pierce, is that detectors are more sensitive to
electrical energy than the telephone, galvanometer, or relay is.

Detectors are necessary only because the energy of the
high-frequency received current is in an unsuitable form for
use with the indicating instruments employed. This is
obvious when we consider such instrmnents as the Hetrodyne
receiver of Fessenden's, which is an indicator so arranged
that the high-frequency currents themselves operate it — no
detector or translating device of any kind being required.

Because the frequency of the oscillations is so high (of the
order of a million per second), the moving coils of galva-
nometers, the diaphragms of telephones, or even the light
fiber of the Einthoven string galvanometer cannot follow them.
No motion, and consequently no indication therefore results.

167

l68 RADIODYNAMICS

The energy must be applied either in such a form that it
acts in one direction on the indicator, as required in the tele-
phone and galvanometer, or, if alternately in opposite direc-
tions, the frequency of the alternations must be so low that
the inertia of the moving parts of the indicator does not come
greatly into play. In the case of the telephone this frequency
should not exceed 2000 per second, about 1000 per second
being the b6st value; with the Einthoven string galvanometer
the best frequency is still lower, in the neighborhood of 100
per second; coil galvanometers have such a slow period, about
I to 10 seconds, that they, for all practical purposes, are be-
yond consideration in this respect.

True, alternating-current instruments depending on the
Thompson effect have been constructed, which give uni-
directional deflections for alternating currents of radio fre-
quency, and, like the Hetrodyne receiver, do not require a
detector, but they are so insensitive that they can be used
only where comparatively large energies are received, such
as in the wave-meter application by I)r. Seibt.^

For the operation, then, of our common and most sensitive
indicators, we require some form of translating device; this is
not, as has been supposed, for the reason that the detector is
a wonderfully sensitive instrument, but because it furnishes
a means of utilizing the marvelous sensitiveness of these
indicators.

Taken singly the detector is perhaps the most important
part of a radiodynamic system. It is to the torpedo what
the ear is to a telephone operator; all orders are received
through it; without it wirelessly directed torpedoes would be
impossible, just as the telephone would be impossible with-
out human ears. It is delicate, necessarily, because of the
slight effects it must respond to; like the human ear it must be

* Elihu Thompson, Eke. World, May 28, 1887; see also Proceedings Inst.
Radio Engineers, Vol. i, Part 3, 1913; and Phys. Review, Vol. 20, p. 226, 1905.

DETECTORS 169

able to stand up under heavy cannonading as well as to hear
weak signals from a distance; it must be rugged to withstand
the severe conditions imposed; rugged, because subject to
strong effects, both mechanical and electrical, which tend to
break down its original sensitive adjustment; rugged for the
reason that the possibility of readjustment in a dirigible
torpedo is excluded.

An ideal detector is one that is extremely sensitive, and at
the same time immune to disturbances which make readjust-
ment a necessity; one that will operate with the faintest
signals, as well as stand up under the strongest electrical and
mechanical shocks.

Although close approaches have been made to this ideal,
the perfect detector has not yet been produced. Those in
use piu-ely for signaling, i.e., radiotelegraphy and telephony,
where an operator is constantly in attendance, are near
enough for all practical purposes, but for such work as torpedo
control, they are not yet what they should be. Even though
the best, namely, those designed or modified especially for.
this purpose, do operate perfectly for hours at a time'imder
the conditions of torpedo control, yet they cannot be de-
pended upon absolutely, and absolute dependence, absolute
reliability in the detector are pre-requisites for a really suc-
cessful dirigible torpedo.

Since the first electric oscillator of Hertz, which consisted
of a bent wire with the ends very near together, a number of
different types of detector have been brought out. These
new types and modifications have been steadily improved in
sensitiveness and reliability.
Detectors may be classified under the following titles:

Coherers. Crystal rectifiers.

Magnetic detectors. Electrolytic detectors.

Thermal detectors. Electrometer detectors.

Thermoelectric detectors. Vacuum detectors.

lyo RADIODYNAMICS

A further classification may also be made which places
detectors under one of two general heads, namely, potential
operated detectors and current operated detectors.

The following table gives this classification according to the
present theories of operation for these detectors:

Potential Operated Current Operated

1. Loose contact coherers. Magnetic.
(Filings, Lodge-Muirhead, mi- Thermal.

crophonic contacts, etc.) Thermoelectric.

2. Capillary electrometer. Crystal rectifiers.

3. Potentio vacuum detector. Electrolytic detectors.

Vacuum detectors.

The potential group operate like a trigger in that they
control local sources of energy which effect indicator oper-
ation, and depend on the potential of the received currents.

The current operated group depend upon the current
effects of the received energy. In some there is a local source
of energy which is called somewhat into play by the action of
the received current. The bolometer, which comes under the
thermal class, is one of these. In others the oscillatory energy
alone affects the indicator operation. Among these is the
crystal rectifier, which, chopping off the even or odd alter-
nations in a received wave train, leaves only impulses of one
sign, positive or negative. In others still, both the incoming
energy and local energy called into play by it act upon the
indicator. The crystal rectifiers with a local battery are
examples of these.

For torpedo control a detector must be able to withstand
the heavy electrical shocks at the shortest ranges, and at the
same time be sufficiently sensitive to operate the relay at
distances up to eight or ten miles. In addition to this it
must not be affected by the mechanical vibration and shocks
met with aboard a small self-propelled craft in a rough sea,

DETECTORS 171

and remain in operative adjustment for at least one hour
under such conditions.

Coherers, as before stated, are suflSciently sensitive, but
their action is erratic; heavy received currents cause detri-
mental effects; as a whole, they are far from the solution of
the detector problem.

Magnetic detectors are very stable, both electrically and
mechanically; they will not burn out with the strongest
signals, nor lose their adjustment when subject to severe
mechanical shocks, such for instance as those arising from
heavy gun fire. Their failing, however, is insensitiveness, in
which they are below most detectors in use.

Thermal detectors, such as Fessenden's barreter and the
bolometer, are mechanically stable, but they are subject to
burnouts from strong signals, and are insensitive. The fine
platinum wire, the resistance changes in which arise from tem-
perature variations produced by the oscillatory currents flow-
ing through it, can be fused by received currents of excessive
intensity. Immunity from these burnouts can only be secured
by increasing the thickness of the fine wire, but this again
reduces the sensitiveness, which at the best is not even equal
to that of the magnetic detector.

Thermoelectric detectors employing a junction of two dis-
similar metals, such as bismuth and antimony, which, when
heated by the passage through it of oscillatory currents,
produce direct thermoelectromotive forces, have, like the
magnetic detector, the necessary stability, but they,, too, are
insensitive. They are also somewhat handicapped in having
a comparatively large heat capacity, so that a signal several
seconds long must be sent before the temperature of the
jimction rises to the maximum value for a given signal in-
tensity; likewise it requires a similar length of time for cool-
ing. Duddeirs thermogalvanometer, which is probably the
most sensitive of the combined thermoelectric detector and

172 RADIODYNAMICS

galvanometer, and of thermoelectric detectors in general,
though valuable for the piuposes of measurements, is not
sufficiently rapid or sensitive for use in a radiodynamic system.
Crystal rectifiers, sometime called also solid rectifiers,
though used in about 90 per cent of radio stations, and though
more sensitive than any of those hitherto described, are still
too low in sensitiveness for use in torpedo control work.
This has been previously pointed out in connection with the
received current curve. These also can* be burned out by
excessively strong signals, so that readjustment is necessary,
and they can be thrown out of adjustment by vibration or
gun fire.

Electrolytic detectors are about equal in sensitiveness to
the crystal rectifiers, but are not so much used as they were
before the advent of the crystal rectifiers. They, too, are
subject to burnouts, and the most sensitive tj^s, the free
point electrolytics, are not mechanically stable. The glass
point electrolytic, in which the fine wire anode is sealed in
glass and immersed in the acid electrolyte, though not possess-
ing this latter defect to so great a degree is less sensitive and
is also subject to burnouts.

The capillary electrometer detector (see Fig. 98), as in-
vented by Armstrong and Orling of England, consists of a
minute capillary glass tube filled with mercury.
The small end of this tube is immersed in an
acid solution. Under the action of a current the
electrolytic polarization of the contact causes a
change of the surface tension of the mercury.
Under this influence the mercury rises or falls in
the capillary tube. A low-power microscope is
used to observe the minute motion of the mer-
cury column. It is said a delicate capillary elec-
trometer will give a readable deflection with an applied e.m.f.
of one ten-thousandth of a volt. In order, however, to pro-

DETECTORS

173

duce a motion sufficiently to act as a relay (one-sixteenth inch),
the e.m.f. must be increased to such an extent that the sensi-
tiveness is too much reduced to make the instrument of value
for mechanism control.

Vacuum detectors* have previously been discussed in detail.
Some are potential operated, others are current operated,
according to the circuit arrangements employed. It has been
shown that with a suitable form of circuit, the vacuum de-
tector approaches nearer the ideal by far than any other

Fig. 99.

detector. Its sensitiveness is as much as 20 times as great
as the best of other detectors, and it is not subject to burn-
outs or severe mechanical shocks. It is this detector and
the circuit which makes it potential operated that has made
possible the extraordinary success attained by Mr. Hammond
in the Gloucester torpedo control experiments. It is pictured
in Fig. 99 as used in the DeForest System.

The hetrodyne receiver of Fessenden, depending on the
principle of beats for its operation, cannot be used for relay
operation, but the beats principle can be applied for ampli-
fication purposes. This will be described in another chapter.

* For detailed accounts of the very important work recently carried out by
Dr. Irving Langmuir, Dr. Lee DeForest, and others, see General Electric Review,
March 1915, May 1915, and Proceedings Inst. Radio Engrs., Sept. 1915.

174 RADIODYNAMICS

The frequency transformer, or tone wheel, of Dr. Gold-
schmidt is another application of the beats principle. Al-
though a very efficient form of detector and very satisfactory
for telephones, it is unsuitable for the operation of oiu: most
sensitive relays, which require direct current, because it, like
the hetrodyne, produces an alternating current for indicator
operation.*

* For complete description of the hetrodyne receiver and U. S. Navy test
data, see Proc. Institute Radio Engineers, Vol. i, part 3, 1913; a complete
description of the Goldschmidt frequency transformer is contained in Proc.
Inst. Radio Engrs., Vol. 2, No. i, 1914.

CHAPTER XXI
METHODS OF INCREASING RECEIVED EFFECTS

Various means for increasing the intensity of received
signals have been proposed and utilized within the past ten
years. These are called amplifiers, amplifones, variable re-
lays, intensifiers, etc., but the generally accepted term is
amplifier. It may be defined as a relay which modifies the
effect of a local source of energy in accordance with variations
in received signals and, in general, produces a larger indica-
tion than could be had from the incoming energy alone.

If a really satisfactory amplifier were available the serious-
ness of the detector problem in radiodynamics would be
greatly reduced, for then a receiving detector possessing the
necessary stability, though lacking in sensitiveness, could be
employed.

To fulfill this requirement, an amplifier must, first of all,
be capable of amplifying with a high ratio; and, next in im-
portance to this, it must neither be subject to burnouts nor
mechanical disturbances; this presupposes no necessity for
readjustment for at least several hours; simplicity is also a
very desirable element.

Amplifiers may arbitrarily be classified as follows:

1. Microphonic contact amplifiers.

2. Generator amplifiers.

3. Vacuum tube amplifiers.

4. Hetrodyne amplifiers.

Of these the microphonic contact amplifiers were the first
to be developed, and they are most used. They consist

17s

176

RADIODYNAMICS

essentially of a combined telephone receiver and transmitter,
the same diaphragm serving both. The rectified received
currents flow through the telephone electromagnet on one
side of the diaphragm the consequent vibratory ipotion of
which alters the resistance of the adjustable microphonic con-
tact on the opposite side. Those in use for radiotelegraphy
usually are so made that they will give a maximum response

Fig. 100.

only for impulses of the correct group frequency. These are
called spark-tuned or monotelephone relays. The common
types employ a diaphragm as the mechanically tuned element.
The Pickard, Ruhmer, Brown, and Telefunken amplifiers are
examples of this type. Others have a steel reed with a very
pronounced period of vibration, to increase the selectivity.
Lowenstein has constructed a very sensitive instrument of
this type. The instrument devised by F. C. Brown is shown
in Figs. 100 and loi.

This type of amplifier has the disadvantage of being subject
to vibration, jars, and sounds; it also requires frequent ad-

MEXHODS OF INCREASING RECEIVED EFFECTS 177

justment. Although exploited commerdally by several lead-
mg radio companies it has never been extensively adopted for
commercial use, even for radiotelegraphy.

The generator amplifier consists of a small generator through
the field coils of which the rectified received currents are
made to flow. The armature currents, with 9JI the charac-
teristics of the field currents, but much amplified, are used
for indicator operation. Alexanderson has built such an

Fig. ioi.
Connection diagram of Brown relay.

amplifier, which he designed especially for telephony, and
succeeded in securing amplification ratios as high as 20 to i.

It is believed that amplifiers based on this generator prin-
ciple present the most satisfactory solution of amplification
problems. They are not subject to mechanical disturbances;
they cannot be burned out, and they can be constructed for
high amplification ratios. Driven continuously by a small
electric motor, a generator amplifier would require no atten-
tion or adjustment. They also lend themselves easily to spark
tuning when a variable condenser is connected across the
field coils.

Vacuum tube amplifiers have been brought out independ-
ently by Lowenstein and DeForest. With three vacuum tube

178

RADIODYNAMICS

detectors arranged in cascade it is claimed amplification ratios
as high as 1 20 to I have been obtained. Such an arrange-
ment is shown in Fig. 102.

These instruments though possessing a high amplification
ratio, and not greatly affected by jars or vibration, have a
multiplicity of adjustments and sometimes are thrown out
of operation by very strong signals, which produce the familiar
"blue arc." Although not so desirable
as the generator amplifier, they are
much more satisfactory than the micro-
phone amplifiers, and may yet be
brought to the desired state of perfec-
tion.*

The beats principle has been applied
by Fessenden for amplification purposes
in radiotelegraphy.

In the latest form of this receiver,
which, as before stated in the chapter on
detectors, is called the Hetrodyne re-
ceiver, a local source of imdamped and
variable high-frequency oscillations is arranged so as to act
on the receiving antenna circuit, and so adjusted that the fre-
quency of its alternations is very nearly equal to the frequency
of the incoming waves . The effect of these two very nearly
equal frequencies, as in acoustics, is to form electrical beats,
or alternate additions and subtractions of the two independent
forces, of a periodicity equal to the difference between the two
original frequencies.

The incoming frequency is fixed, but the local frequency
can be altered at will, and any beat frequency desired can be
produced to suit the acoustic conditions.
When no beats are produced the two frequencies are equal;

* For complete description of the DeForest Audion Amplifier, see ProCt
Inst. Radio Engrs., Vol. 2, No. i, 1914, page 24.

METHODS OP INCREASING RECEIVED EFFECTS 179

obviously by calibrating the local source of oscillations, a
very useful means of measuring the exact wave length of a
distant transmitter is furnished.

It is said amplification ratios as high as 20 to i have been
secured with such an arrangement. The principal difl&culty
with this system, however, is a reliable generator for the local
oscillatory currents at the receiver. Arcs are troublesome
and require constant attention; high-frequency alternators
are very cumbersome (existing types weighing at least looo
pounds, and possessing a rotor which makes 20,000 r.p.m.)
and at the same time expensive. For this reason it woidd
be next to impossible to utilize this amplifying principle for
torpedo control, unless some simple and reliable wave gen-
erator be developed.*

* See Proc. Inst. Radio Engrs., Vol. i, Part 3, 1913. The author in 191 1
under the direction of Mr. Fritz Lowenstein experimented successfully with
vacuum tube rectifiers as a means of producing sustained high-frequency os-
cillations for use in beat amplifying and selective systems and also as a wave-
generator for radiotelephony. (For a very complete consideration of micro-
phonic contact ampiiners, see extracts from a paper presented before the I. of
E.E., London, which appeared in the Elec. Rev. and Western Elect., Vol. $6,
Nos. 23 and 24, "A Telephone Relay," I and U.)

CHAPTER XXn
RELAYS

The importance of a relay in a radiodynamic system is
9ec(md only to that of the detector, and its requirements are
just as exact. That is, it must have great sensitiveness,
ruggedness, stability, and small inertia.

The sensitiveness necessary in the relay to bridge a given
distance depends upon a nxunber of factors, namely, the
height and power in the transmitting antenna, and the
efficiency of the receiving detector, or detector and amplifier.
Obviously these factors must be taken into consideration
for the reason that they are interdependent. For torpedo
control it is of little consequence what the sensitiveness of any
single one of the receiving instruments is so long as the final
result, namely, the opening and closing of the relay contact,
can be reliably effected from the transmitter at the required
distance, and so long as the combination is immune to dis-
turbances of whatever nature which must be encountered.
The sole function of the detector, amplifier, and relay in
mechanism control is to open and close an electric circuit
at the will of the control operator. Any combination of the
above-named instruments that will accomplish this result
with absolute reliability is a satisfactory solution of the prob-
lems involving each of the three elements separately. That
combination, however, which is most simple, least cumber-
some, and least expensive is to be preferred.

In radiodynamic work where the distance is not limited
by vision, as it is with torpedoes, each of the elements should
have the maximum sensitiveness in order that the distance

i8o

RELAYS

l8l

of operation may be as great as possible. The desirability
of this is evident for such use as call-bell operation in radio
signaling.

Relays are commonly classified as polarized and non-
polarized. The motion of the movable element in the former
reverses with a reverse in the direction of the current energiz-
ing it, while in the latter the motion is always unidirectional.

In the polarized relays either an armature consisting of a
permanent magnet, or a coil through which the current flows,
is the movable element.

No. 554.

Fig. 103.
Polarized relay of the high-resistance type.

{Courtesy J. H. Brunnell &• Co.)

The non-polarized types usually have a soft iron armature
or core which is always attracted in one direction regardless
of the direction of the current in the electromagnet or solenoid
influencing it.

The most sensitive non-polarized relays, such as those used
in telegraph oflSces, require a current of three or four milH-
amperes to trip them. The most sensitive of the polarized
type, as developed for use with coherer receivers by the
Marconi, Slaby-Arco, Ducretet, Telefunken, and other com-
panies, require about 400 microamperes under operating con-

i82 RADIODYNAMICS

ditions. Such a rday is shown m Fig. 103. Movable coil
relays, with permanent magnet fields and solid local circuit
contacts as previously described are more sensitive than
the above ferric armature types, requiring in the neighbor-
hood of 200 microamperes for operation. When fitted with
strong electromagnetic fields and a mercury-platinum contact
arrangement, the movable coil relays can be made to operate
reliably on from about 30 to 5 microamperes, depending on
the mechanical disturbances encountered.

A very sensitive galvanometer of ordinary construction
and about 1000 ohms resistance will give a visible deflection
with less than one ten-millionth of a volt, but such an instru-
ment requires a very solid support, such as a heavy masonry
pillar, and the slightest vibration or current of air will cause
the delicately suspended coil to move. Suspension coil gal-
vanometers, though possessing very high sensitiveness, can-
not be used for relays because of their extreme delicacy.
Even uni-pivot galvanometers, such as the portable Paul
instruments, which will give a 90-degree deflection for 10
microamperes, though at least ten times as sensitive as the
author's modification of the Weston dual-pivot relay, cannot
be used for relay purposes except under ideal conditions in
the laboratory. They require leveling screws, and though
not to quite so great a degree as the suspension coil galvanom-
eter, are still much too delicate for use aboard a torpedo.

Likewise galvanometers of the vibration type like Eintho-
ven's, which are capable of use in radio receiving stations for
recording messages photographically over great distances, are
not rugged enough for torpedo control work.

The capillary electrometer can be used as a relay, but, as
before stated, its sensitiveness is not sufficiently high. -

It is believed that the remodeled Weston relay, as used by
Hammond, is the most satisfactory instrument for this kind
of work.

CHAPTER XXin
TORPEDO ANTENNJE

It is not the purpose here to discuss the many details in
connection with the ordinary types of antenna used for radio
work and means for supporting them. I wish merely to
make a few remarks on antennae for special use in torpedo
control work, and briefly to describe the most recent pro-
posals for improvement of this essential part of the receiving
apparatus.

Obviously, as shown long ago by Marconi, the receiving
antenna should be as high as possible, since the received cur-
rent increases with the height. Marconi enunciated at one
time an empirical law that, for simple vertical sending and
receiving antennae of equal height, the maximum working
telegraphic distance varied as the square of the height of the
antennae. The experiments of the General Electric Co., of
Berlin, also roughly agree with Marconi's law. Dr. L. W.
Austin has worked out a formula, which, taking into account
the antenna heights as well as the transmitting power and
atmospheric absorption, gives the approximate signaling
range of any transmitter and receiver.*

The length of the horizontal portion of an antenna is also
of some importance.

We see then that for our torpedo we require an antenna of
the greatest possible height and length. It is very doubtful
whether, with the type of craft used for torpedoes, this height

* For a discussion of this equation, see Austin, L. W., Bulletin Bureau
Standards, 191 1, Vol. VII, No. 3, pp. 315-363, "Some Quantitative Experi-
ments in Long Distance Radio Telegraphy."

183

i84

RADIODYNAMICS

could be made to exceed the length of the vessel. The best
practice, as shown in the antennae, in use on the submarine
boats of the navies of the world, substantiate this statement.

The 40-foot Radio in the Gloucester
experiments had a three-wire inverted
L-type antenna, with 6-foot spreaders
of light bamboo; it was about 20 feet
above the water and about thirty feet
long, supported by two 3-section masts
made of the lightest steel tubing con-
sistent with strength. These weighed
about 15 pounds each. The antenna
wire was of the usual phosphor-bronze
variety having 7 strands ot No. 22
wire. A single 1,000,000- volt strain
insulator between each spreader and
mast-head blocks furnished the neces-
sary overhead insulation. For the
leading-in insulation a 500,000-volt roof
type leading-in insulator was used.
This was protected from the flying
spray by an improvised hood. These
insulation precautions were taken as a
result of experiments which proved
their necessity with the potential-
operated vacuum detectors.

Experiments were made with this
antenna in the effort to increase its
effective length. By increasing its
length it would be possible to increase
its natural wave length and thus di-
minish the value of the energy absorbing loading inductances
necessary for tuning to the transmitted waves.

In this connection a field worthy of experimentation is one

\MM''-

K ' V^ -

1 ^

i"^^

|»

fjTOiKSU_gif gwB 'iw^

Fig. 104.

Common type of radio

tower.

TORPEDO ANTENNM 185

which covers the possibilities relative to variation of trans-
mitting wave length between two antennae of widely different
natural periods.*

It is well known that a transmitting antemia will operate
most jeffidently only at that wave length corresponding to
the natural period of the antenna with just sufficient induc-
tance in series for coupling to the closed circuit. If th^ wave
length be increased energy-absorbing loading inductances are
necessary; if decreased, an energy-absorbing series capacity
must be used.

The receiving oscillatory system likewise has a definite
wave length for which it will operate most efficiently, and for
the same reasons. It is known, however, that the current in
an oscillatory circuit is inversely proportional to the wave
length, so that although the receiving antenna is operating
inefficiently at a wave length below its natural wave length,
it is possible that the receiver, as a whole, works at an in-
crease in efficiency. Again, while the receiver works best
with short wave lengths, the power that can be handled by a
transmitting -antenna decreases with its natural wave length,
and so it is possible that the large transmitting powers made
possible by high, large capacity, long wave length antennae
will entirely overbalance the detrimental effects due to in-
efficiency in the reception of the waves. This presents an
interesting field for experimentation.*

At the suggestion of Dr. Lee DeForest, the "Radio's"
antenna was fitted with an extension in the form of two long
wires attached to the after spreader and reaching down to a
light wooden float 30 or 40 feet astern; the swift motion of the
boat kept the wires taut. Long pennant-like pieces of cloth

* See "Optimum Wave-length in Wireless Telegraphy," by A. H. Taylor,
Physical Review, Vol. i. No. 4, Apr. 1913, pp. 321-325. Also, "Determination
of Wave-length in Radio Telegraphy," A. S. Blatterman, Electrical World,
Vol. 64, No. 7, Aug. IS, 1914, pp. 326-329.

l86 RADIODYNAMIC^

through which light wires connected to the rear end of the
antenna were woven, and which stood out almost horizontally
from the mast head when the boat was in naotion, were also
tried. Neither method, however, was foimd of any material
benefit.

Water Antenna. A very novel form of antenna was in-
vented several years ago by Fessenden. It consists of a
stream of water thrown vertically upward through a coil of
copper tubing by a centrifugal force pump. Although possi-
bly inoperative in fresh water a torp)edo so equipped might be
practicable in salt water, which has a higher conductivity.
The hollow coil serves as a means of coupling the water
antenna to the receiving apparatus.

The apparent advantage of such an aerial conductor is that
it cannot be shot away by the enemy. No data relating to
actual use, either experimental or practical, of an antenna
of this type can be found.

The U. S. Navy has experimented with submerged receiving
antennae, for use in signaling to submarine boats equipped
with radio apparatus. The antenna consisted of a type of
conductor, very heavily insulated with rubber and other in-
sulating compounds, known as "rat- tail." The antenna wire
was thus completely insulated from the water, although be-
neath its surface. The author assisted in these tests which
were made at Washington, in 1909. Audible signals were
received with such an antenna in the Potomac riv6r at Alex-
andria, Va., about seven miles from the two-kilowatt trans-
mitter at the Washington Navy Yard.

These tests after considerable experimenting at Charleston
and Boston with submarine boats were finally discontinued.

Another type of antenna, which has a marked directive
effect, and experimented with by Dr. Franz Kiebitz, of the
General Telegraph Department, of Berlin, has aroused con-
siderable interest within the past two years. A straight wire

TORPEDO ANTENNM ' 187

is stretched horizontally a few feet above the earth, and the
receiving apparatus connected in the middle. The best
directions of reception are those to which the free ends of the
wire point. In other forms the two ends are groimded; in
still others only one end is groimded, the receiving apparatus
being connected near that end.*

* See Proc. Inst. Radio Engrs., Dec. 191 5: '* The Eflfectiveness of the Ground
Antenna in Long Distance Reception."

CHAPTER XXIV
RECENT DEVELOPMENTS

Pneumatic Steering Apparatus. — The latest development
in torpedo-control apparatus has been to discard electric
steering gear, and to adopt apparatus designed for use with

Fig. 105.

•The head telephones enable the operator to listen to the control impulses; the

instrument in front of the operator is a searchlight control apparatus.

compressed air. In Figs. 105 and 106 may be seen a control
operator at the Hammond Laboratory. Fig. 107 is a view
of this Laboratory, and Fig. 108 is a view of Hammond's
latest boat.

188

RECENT DEVELOPMENTS 189

This change has made possible a great simplification of
apparatus, and a corresponding increase in reliability; inci-
dentally it has also increased the accuracy of control because
of the swiftness with which the operations are performed.

Fig. 106.

The gratifying results now being secured with pneumatic
apparatus are ample evidence of the truth of the afore-
mentioned statement that simplicity is a highly important
factor in apparatus where adjustment is not possible; and
that even very simple electric devices are uncertain in their
action.
There are only three operations necessary for the control

190

RADIODYNAMICS

of a dirigible torpedo, namely: (i) rudder to port, (2) rudder
to starboard, and (3) engine control. The following is one

Fig. 107.

of a number of pneumatic systems devised by the author
with this "simplicity" idea in mind. In addition to the

:^f

\ 1

^ ... ..... 1^

, . 1

_Jr, * ^v '

*■

■!ff^..^-''r iK€K

ST^-^id

■^ * • * *

^^^^%mmmf4\ BT

^^^^^^^^^m0r

Fig. 108.

simple and rugged nature of the apparatus it also possesses
the advantage that, unlike other systems, it does not require

RECENT DEVELOPMENTS

191

an especially trained operator; even with the simplest of the
old systems, such as Gardner's and Hammond's, a very con-
siderable amount of practice is necessary in order to attain
expertness in the boat's control.

This system was designed in 191 2 for use with selector
systems in which a gradual back and forth rectilinear motion
of the movable selector element, as distinguished from the

W/re/ess Con fro/led
Re /ay

^-^ww^wooDoowoomooonoir-O

Rudder

Fig. 109.

Step by step circular motion of some, can be secured. Three
of the author's methods as well as that of Gardner's, are
adaptable for this purpose.

As shown in Fig. 109 the function of the movable selector
element is to control air valves, which in turn control the
energy used in performing the desired operations. A brief
description will serve to explain the action of the apparatus.

Normally the transmitting impulses are of such character

192 RADIODYNAMICS

that the valve V is partially open, thus allowing compressed
air to escape from the tank to the cylinder. At this normal
position the pressure inside the cylinder reaches a certain
value and then remains constant, due to the pull of the
large spring S, and to the action of the adjustable escape
valve E. If the valve V is opened wide the piston moves
quickly, and with great power to the left, due to the fact
that the escape valve cannot take care of this increased
inrush of air; if the valve is closed farther than the normal
position, the piston will be moved in the opposite direction
by the spring S. By this means, the rudder, as shown, can
be made to move to either side as swiftly or as slowly as de-
sired, and maintained in any position, simply by altering the
position of the steering wheel at the transmitting station.
This alters the speed, or the ratio of on to off periods, of the
impulses. Thus any inexperienced operator can steer the
boat.

For engine control a rotary valve (not shown) operated by
the solenoid, is used. This has but two kinds of positions
corresponding to start and stop. When it is desired to start
the engine, one turn of the steering wheel to the extreme
right (farther than for the hard over position) is made; the
operation for stopping is exactly the same. This can be
done quickly so that no interference with the steering evolu-
tioned need be experienced. The required air pressure is
maintained in the tank by a compressor actuated by the
propelling motor.

Another system of the writer's depends on the selecting
action of a dash-pot retarded solenoid apparatus. By send-
ing an impulse of one second, then allowing a short break,
and then holding the impulse again, number one circuit can
be operated. For the other circuits the first impulse need
only be changed to 2, 3, 4, etc., seconds, according to the
number of the circuit to be operated. The circuit continues

RECENT DEVELOPMENTS 193

to be closed as long as the last impulse is held; when it is
stopped the selector arm returns to the normal position.

Not mentioning the work now being carried on both in the
United States and in Europe on the control of trains by
control systems based on electromagnetic induction at dis-
tances of a few feet, the latest development along the lines
of distant control has been reported from France and Italy
in connection with the "F ray" naval experiments made in
the Solent. It may be worth recalling that Signor Ulivi
made a number of experiments in the presence of the French
authorities at Villers-sur-Mer in August of 1913.

"The 'F rays' were originally discovered by a professor at
the University of Nancy, and there has been considerable
controversy from time to time as to their potency, and some
have even doubted their existence. On the other hand, ac-
cording to certain reports, the effects obtained by Signor
Ulivi were wonderful, and amazed the French authorities.
No less a personage than CJeneral Joffre is said to have been
impressed by them, and to such an extent that he asked the
inventor to prepare a plan by means of which an enemy's
magazines and powder supplies might be blown up from a
distance.

"What Signor Ulivi has since done in France has remained
a profound secret; in fact it is not known whether he has done
anything at all. Immediately after the first articles had
appeared in the papers, in August of 1913, it is understood
he was asked to go to England to submit some tests to the
British Admiralty. His experiments in France were chiefly
carried out at Havre and Villers-sur-Mer. They were wit-
nessed by General Joffre, General Curieres, de Castelnau,
Major Ferrie, and a delegate of the Minister of War, Captain
Cloitre. The first tests consisted of a series of submarine
mines of which there were ten, placed at intervals of 600
meters. Signor Ulivi, at the appointed moment, touched

194 RADIODYNAMICS

a lever, and one by one the mines exploded without any
visible agent. He declared that he had done it by a con-
centration of the power of F rays. He was next asked to
blow up some powder magazines in an old hulk, which he
also did successfully.

" The technical officers who had witnessed the tests next
wanted to prepare mines in their own way and defied hi6i to
explode them. This he is alleged to have refused to do at
one moment, and a discussion arose. Were the experiments
sincere or not? The question was asked and sides were taken
at the time; but the dispute was suddenly hushed up or
dropped. The fact is that every subsequent move of Signor
Ulivi has been shrouded in mystery."*

Self-Directing Torpedoes.

The latest tendencies along torpedo-control lines have been
towards the development of apparatus which will give a tor-
pedo the power of self -direction.

In 191 2 the author, in collaboration with John Hays Ham-
mond, Jr., developed such an apparatus, which was called
an '^orientation mechanism." It is more generally known
now as the "electric dog." It is shown in Figs, no, in
and 112.

"This orientation mechanism in its present form, consists
of a rectangular box about three feet long, one and a half
feet wide, and one foot high. This box contains all the in-
struments and mechanism, and is mounted on three wheels,
two of which are geared to a driving motor, and the third,
on the rear end, is so mounted that its bearings can be turned
by electromagnets in a horizontal plane. Two five inch
condensing lenses on the iforward end appear very much like
large eyes.

* Extract from an article in the "London Times."

RECENT DEVELOPMENTS

195

"If a portable electric light be turned on in front of the
machine it will immediately begin to move toward the light,
and, moreover, will follow that light all around the room in
many complex manoeuvers at a speed of about three feet per

iPT'

•deUniwm C«ll .

P^n^ R«lat)

R«l«*|«

Wirir\9 Did9ram- CUctric D09

Fig. 1 10.

second. The smallest circle in which it will turn is of about
ten feet diameter; this is due to the limiting motion of the
steering wheel.

Upon shading or switching off the light the dog can be
stopped immediately but it will resume its course behind the

196

RADIODYNAMICS

moving light so long as the light reaches the condensing
lenses in sufficient intensity.

"The explanation is very similar to that given by Jaques
Loeb, the biologist, of reasons responsible for the flight of
moths into a flame. According to Mr. Loeb's conclusion,
which is based on his researches, the moth possesses two
minute cells, one on each side of the body. These cells are
sensitive to light, and when one alone is illuminated a sensa-

FlG. III.

Interior of Electric Dog.

tion similar to our sensation of pain is experienced by the
moth; when both are equally illuminated, no impleasant
sensation is felt. The insect therefore keeps its body in
such a position, by some manner of reflex action, as will in-
sure no pains, and in this position the forward flying motion
will carry it directly toward the source of light.

"The orientation mechanism possesses two selenium cells,
corresponding to the two light sensitive organs of the moth,
which, when influenced by light effect the control of sensitive
relays, instead of controlling nervous apparatus for pain pro-

RECENT DEVELOPMENTS 197

duction, as is done in the moth. The two relays controlled
by the selenium cells in turn control electromagnetic switches
which effect the following operations; when one cell or both
are illuminated the current is switched onto the driving
motor; when one cell alone is illuminated, an electromagnet
is energized and effects the turning of the rear steering wheel.
The resultant turning of the machine will be such as to bring
the shaded cell into the light. As soon and as long as both

Fig. 112.
Electric Dog in Action.

cells are equally illuminated in sufficient intensity, the ma-
chine moves in a straight line toward the light source. By
throwing a switch, which reverses the driving motors con-
nections, the machine can be made to back away from the
light in a most surprising manner. When the intensity of
the illumination is so decreased by the increasing distance
from the light source, that the resistances of the cells approach
their dark resistances, the sensitive relays break their respec-
tive circuits, and the machine stops.
"The principle of this orientation mechanism has been.

iqS radiodynamics

applied to the Hammond dirigible torpedo for demonstrat-
ing what is known as attraction by interference. That is,
if the enemy tries to interfere with the guiding station's con-
trol, the torpedo will be attracted to it. The torpedo is fitted
with, apparatus similar to that of the electric dog, so that if the
enemy turns their search light on it, it will immediately be
guided toward that enemy automatically.

'* In order that the search light used by the control opera-
tor may not have this same effect, use is made of a gyroscope
to keep the turn table upon which the cells are moimted,
in a fixed position relative to the earth. In this way no mat-
ter how much the torpedo turns; or in what direction it is
traveling the selenium cells will always face from the shore
and toward the attacking battleship in the open sea.

*'By means of two directive antennae, instead of two sele-
nium cells the same principle may be applied for attraction
by interference when Hertzian, instead of light waves are
used. Soimd waves might also be utilized in a similar man-
ner so that the sound reaching the torpedo (which would be
equipped with two submerged microphones made sensitive
and directive by megaphone attachments) from the pound-
ing of the battleships engines and other machinery, would
effect its attraction in a way analogous to the attraction of a
source of light for the orientation mechanism. It is just
possible, too, that similar apparatus could be used for the
detection of submarines, or for defense against them." *

The electric dog operates in a single plane, the horizontal;
the author has developed plans for extending its operations
to both horizontal and vertical planes, by using two sets of
the orientation apparatus operating at right angles to one
another. These plans include the use of all forms of radiant
enerjgy.

♦ Extract from a paper on Torpedo Control by the author in the Purdue
Engineering Review, 1914.

RECENT DEVELOPMENTS 199

With such a double orientator a new defense against the
submarine becomes possible. Captain K. O. Leon of the
Swedish navy has ahready applied the electric dog principle
to the automatic direction of torpedoes, the soun4 waves
sent out through the water from the hull of a ship acting as
the attracting stimidus; it, is but a step to apply a double
'orientator of this type to torpedoes that will seek out and
destroy any submarines within its range of hearing. This
same type of automatic director is suitable for use with
aerial torpedoes, explosive-laden mechanical moths, which
will sweep down upon the ships of the air with a sting that
will blow them into a thousand pieces. The electric dog
which now is but an uncanny scientific curiosity may within
the very near future become in truth a real "dog of war,"
without fear, without h^rt, without the human element so
often susceptible to trickery, with but one purpose; to over-
take and slay whatever comes within range of its senses at
the will of its master.

INDEX

Adams, Prof., experiments of, in
electromagnetic induction signal-
ling, IS.
Amplifiers, classification of, 175.

De Forest's, 50.

Generator, 177.

Hetrodyne, 178.

Lowenstein's, 62.

Microphonic, 175.

Monotelephonic, 141.

Vacuum tube, 177.
Antennae, Austin's law for height of,

183.

Circuit adjustment of, 134.

Marconi's law for height of, 183.

Of Kiebitz, 186.

On ''Pioneer'' 125.

On ''Radio,'' 185.

Submerged receiving, 186.

Torpedo, 183.

Water (Fessenden), 186.
Armstrong and Orling, capillary elec-
trometer, 172.
Austin, Dr. L. W., experiments by,
with radiotelegraphic sender, 72.

Formula of, for antennae height,

183.

Automatic recording telegraph, 3.

Balloon, dirigible, of Roberts, 86.
Battle-range torpedo control, 124.
Bell, Alexander Graham, experiments
of, in electromagnetic induction
signalling, 15.
Photophone of, 9.
Plan of, for marine signalling, 17.
Beck, experiments of, in torpedo con-
trol, 100.

Berger, H. Christian, apparatus of,

in earth conduction, 71.
Bolometer, 10, 41, 51.
Boys, radiomicrometer of, 51.
Branley, codal selector of, 141.

Control system of, 105.

Protective device of, 106.
Branly, experiments with Hertzian

waves, 27.
"Branly tube," or coherer, 28.
Bull, Anders, codal selector of, 141.

Capillary electrometer (Armstrong &
Orlmg), 172.

As relay, 182.
Cells, silenium, 57.

Selectivity of, 63.
Codal selector, of Anders Bull, 141.

Branley, 141.

Walter, 141.

Wirth, 141.
Coherers, 171.

Branly's, 28.
Control energy, choice of, 34.
Control systems, classification of, 89.

Beck's, 100.

Branley 's, 105.

Deveaux's, 96.

Hammond's, of torpedoes, 122.

Knauss's, 100.

Wirth's, 100.
Cooke, W. F., needle telegraph of, 3.
Crooke's radiometer, 10, 51.
Crystal rectifiers, 172.
Current, density of, 8, 9.

d' Arson val, radiomicrometer of, 51.
Davy's sound-relaying system, 10, 11.

202

INDEX

De Forest, amplifier, 50.

Vacuum-tube rectifier, 129.
Density of current between earth-
plates, 8, 9.
Detectors, 167.

Capillary electrometer, 172.

Electrolytic, 172.

Ion controller (Lowenstein), 24.

Magnetic, 171.

Potentio, 134.

Radiant heat, 46.

Thermal, 171.

Thermoelectric, 48, 171.

Vacuum, 173.
Deveaux's dirigible torpedo boat, 96.
Diathermanous materials, 45.
Dirigible torpedo boat (Deveaux),

96.
Dolbear, Prof., electrostatic system

of, 19.
Double orientation mechanism, 194.
Duddeirs thermogalvanometcr, 10,

171.
Duddell-Thompson arc, 142, 147,
160, 163.

Earth conduction, 3, 67.

Experiments in selective control,
offered by, 67.

Low resistance of, 8.

Plan of Berger, 71.

Plates (Steinheil), 9.
Edison, dirigible torpedo c/, 86.

"Tasimeter" of, 10, 52.
"Electric Dog," 194.
Electric wave producers, 159.
Electrolytic detector, 172.
Electromagnet, invention of, 3.
Electromagnetic induction, 76.

Laws of, 3.

Telegraph, 3.

First overland system of, 3.
Development of, 4.

Signalling, 15.

Electromagnetic sounder, 4.
Wave systems, 27.
Later improvements in, 32.
Marconi, early experiments of,

31-

Tesla, experiments of, 28.
Electrometer, capillary, 172.

As relay, 182.
Electrons, effect of ultra-violet rays

on, 64.
Electrostatic tei^raph systems, 19.
Of Le Sage, 4.
Of Lowenstein, 23.
Electrostatic and electromagnetic in-
duction, 74.

"F Ray," discovery of, 193.

Experiments of Uiivi in, 193.
Faraday, discovery of laws of elec-
tromagnetic induction by, 3.
Fessenden, Prof., hetrodyne receiver
of, 167, 173, 178.
Interference preventer of, 142.
Submarine signalling system of, 36.
Water antennae of, 186.
Franklin, Benjamin, experiments of, 2.

Invention of torpedo by, 78.
Frequency transformer (Gold-

schmidt), 174.
Fulton, Robert, experiments by, with
torpedoes, 78.

Gale, Prof., experiments of, in water

conductivity, 13.
Galileo, early theory of, 6.
"Galvanic excitation" of Steinheil, 8.
"Galvanic induction of" Steinheil, 8.
Galvanometers, 2.

As relays, 182.
Gardner, John, sensitive vibratory re-
lays of, II.

Torpedo control, system of, 93.
Galvanoscope, 2.
Gauss, experiments of, 2.

INDEX

203

Generator amplifier, 175.
Goldschmidt, Dr., frequency trans-
former of , 174.
Goose quills, use of, for insulation, 3.
Gray, Stephen, early discovery by, 2.

Hammond, John Hays, Jr., experi-
ments by, 107.
Steering apparatus of, 114.
Torpedo control, system for coast
defence, 122.
Hammond radio research laboratory,

work of; 107.
Heat, detectors of, 10.
Heliograph, i.
Henry, invention by, 3.
Hertzian waves, 77.
Branl/s experiments with, 28.
Lodge's experiments with, 28.
Hetrodjme receiver (Fessenden),
167, 173, 178.

Indians, signalling by, i.

Indicator currents in radio receivers,
experiments of G. W. Pierce in,
ISO.
Nature of, 150.

Induction-conduction telegraph sys-
tems (Preece's), 25.

Inductive effects in telephone circuits,

IS-
Infra-red or heat waves, selectivity
of, 44.
Use in torpedo control, 41.
Interference preventer, 159.

Of Fessenden, 142.
Ion controller detector (Lowenstein),
24.

Knauss, experiments of, in torpedo
control, 100.

Leon, Capt. K. O., experiments with
torpedoes, 199.

Le Sage of Geneva, 2.

Electrostatic telegraph of, 4.
Leyden jar, discovery of, 2.
Light telephony, 60.
Lindsay, James Bowman, experiments

of, in water conductivity, 14.
Lodge, Sir Oliver, experiments with

Hertzian waves, 28.
Lowenstein, amplifier of, 62.

Electrostatic telegraph of, 23.
Ion controller detector, 24.

Magnetic detectors, 171.
Marconi7 early experiments of, 31.
Law of, for height of antennae,

183.

Marine signalling. Bells plan for, 17.

Method of Rathman, 18.

Method of Ilubens, 18.

Method of Strecker, 18.
Microphonic amplifier, 175.
Micro-radiometer (Weber), 47.
Monotdephone amplifier, 141.
Morse, foundation of overland system,

3.
Development of overland system of,

4.
Sounder of, 4.

Experiments of, with earth con-
duction, 12.
Report of, to government, 12.
"Multipliers'* of Steinheil, 8.
Muschenbroek of Leyden, 2.

Nichol's radiometer, 51,

Orientation mechanism (" Electric
Dog"), 194.
Applied to Hammond dirigible tor-
pedo, 197.
Double, 198.

Experiments of Captain Leon with,
199.
Oersted, discovery by, 2, 4.

204

INDEX

Parabolic reflectors, 42.
Photophone, of Bell and Tainter, 9.
Pierce, Prof., G. W., experiments of,

in indicator currents in radio re>

ceivers, 150.
Pliny, early discovery by, 2.
Pneumatic steering apparatus, 188.
Potentio detector, 134.
Adjustment of, 135.
PoppofiF's receiver, description of, 30.
Preece's induction-conduction system,
description of, 25.

Radiant energy in ether and air,

vibration frequencies of, 33.
Radiant heat detectors, 46.

Classification of, 47.
Radio control, experiments in Europe,

193-
Recent developments in, 188.
Radiodjoiamic torpedo (Tesla), 85.
Radiodynamics,^ sound waves in, 36.
Radio-Goniometer (Bellini and Tosi),

44, 140-
Radiometer, 51.
Radiomicrometer of d'Arsonval and

Boys, 51.
Radio receivers, indicator actions of,
163.

Indicator currents in, 150.
Radiotelegraph, experiments with,
(Austin), 72. .
First, 10.

Power of transmitter, 35.
Range of received power, 35.
Radio tower, common type of, 184.
Rathbone, Charles, discovery by, 14.
Receivers, hetrodyne (Fessenden) ,
167, 173, 173.
Poppoff's, 30.
Selective, 137.

** Whip-crack " efifect in, 137.
Receiving wave detector, Varley's use
of, 27.

Rectifiers, crystal, 172.

Vacuum tube of De Forest, 129.
Reflectors, parabolic, 42.
Relay, capillary electrometer as, 182.

Galvanometer as, 182.

Importance of, 180.

Improvements of, 1 26.

Invention of, 5.

Non-polarued, 181.

Polarized, 181.

Resonance, 141.

Sensitive vibratory, of Gardner, n.
Resonance relay, 141.
Roberts, dirigible balloon of, 86.
Romagnesi of Trent, discovery by, 2,
4-

Sacher, Prof., E., experiments of, in
induction, 15.

Schilling, telegraph of, 2.

Schweigger, discovery by, 2, 4.

Searchlights, electric atmospheric ab-
sorption and dispersion of rays,

45.
Invisibility of rays, 43.
Selective receivers, 137.
Selective transmitter-receiver unit,

145-
Selectivity, means of obtaining, 145.
Selectors, 89.
Branley's, 92.
Codai, 141.
Hulsmeyer's, 93.
Walter's, 92.
Self-directing torpedoes, 194.

Experiments of Capt. Leon with,

199.
Orientation mechanism applied to,
199.
Semaphore system, i.
Signalling, early methods, i.
Flag, I.

Submarine (Fessenden's apparatus
for), 36.

INDEX

20S

Silenium, 57.

Cells, 57.

Selectivity of, 63.
Sims, dirigible torpedo of, 86.
Siren interference machines, 143.
Sonorescent property of substances,

10.
Sound waves in radiodynamics, 36.
Sound-relaying system, of Davy, 10.
Souftder, electromagnetic, of Morse, 4.
Steering apparatus (Hammond), 114.

Pneumatic, i88.
Steinheil, system of telegraphy of, 2.

Radio-telegraphic system of, 10.

Scheme of earth-plates of, 9.

Use of railway by, 3.

Wireless telegraph of, 6, 9.
Sturgeon, invention by, 3.
Submarine signalling. Prof. Fessen-
den's apparatus for, 36, 40.

Tainter, Sumner, photophone of, 9.
"Tasimeter," Edison's, 10, 52.
Telautomaton (Tesla), 84.
Teledynamics, development of, 4, 5.
Teledynamic system, principal parts

of, 33-
Telefuncken, transmitter of, 139.
Telegraph, automatic recording, 3.

Electrostatic, 4-23.

Electromagnetic, 4.

First invented, 2.

First overland, 3.

First in U. S., 4.

Needle, 3.

Wirdess, 6, 12.
Telephone, inductive effects in, 15.

Invention of, 14.

Wireless, 14.
Telephony, light, 60.
Tesla, Nikola, early experiments, 28.

Invention of wirelessly controlled
vessel, 83.

Radiodjoiamic torpedo ot, 85.

Tesla, Nikola, Telautomaton of, 84.
Thales, early discovery by, 2.
Theophrastus, early discovery by, 2.
Thermal detectors, 166, 171.
Thermocouple, 49.
Thermoelectric detectors, 48, 171.
Thermogalvanometer, Dudddl's, 171.
Thermo-electric pile, 9.
Thermopile, 41, 48.

Of Coblentz, 49.

And galvanometer relay, 51.
Thermostat, 53.

Torpedo, advantages and disadvan-
tages, 83.

Antennae of, 183.

Battle range, control of, 124.

Coast defense (Hammond), 122.

Control systems for, 93, 96, 100.

Demonstrations of, before U. S.
War dept., 121.

Description of, 79.

Dirigible, 86, 102.

Experiments of Lebn with, 199.

First test of, 78.

Invention of, 78.

Methods of launching, 80.

Radiodynamic (Tesla), 85.

Self-directing, 194.
Transmitter of Telefuncken, 139.
Trowbridge, Prof., John, study of
electromagnetic induction signal-
ling, IS-

Ultra-violet radiations, 64-66.
Ulivi, experiments of, in F Rays,
193-

Vacuum-detector, 173.

rectifier, of De Forest, 129.
Vacuum-tube, amplifier, 177.
Varley's use of receiving wave detec-
tor, 27.
Vibration frequencies of radiant

energy in ether and air, 33.

2o6

INDEX

Walter, codal selector of, 141.
Watson of LlandafiF, early discovery.

by, 2.
Wave systems, electromagnetic, 27,

28, 31, 32.
Waves, infra-red, 41, 44.
Weber, micro-radiometer of, 47.
Wheatstone, needle telegraph of, 3.
Automatic recording telegraph of,

"Whip-crack" efifect in receivers, 137.

Wilkins, J. W., experiments of, with
earth conduction, 14.

Willoughby Smith, discovers proper-
ties of silenium, 57.

Wilson, Ernest, invention by, of wire-
less control of vessels, ^^*

Wireless telegraphy, 6.
First, of Steinheil, 6.
Later, of Steinheil, 9.
Practical, 12.
Wireless transmission of energy, ex-
periments of Nikola Tesla, 28.
Wirelessly controlled vessels, system
for(Wilson), 83.
Invention of (Tesla), 83.
Description of, 84.
Wirth, codal selector of, 141.
Experiments of, in torpedo control,
100, 102.

Zickler, Prof. E., use of ultra-violet
rays in telegraphy, 65, 66.

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Full text of "Radiodynamics, the wireless control of torpedoes and other mechanisms"

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