LIBRARY
OF THE
UNIVERSITY OF CALIFORNIA.
Class
THE TELEGRAPHIC
TRANSMISSION OF
PHOTOGRAPHS
THE TELEGRAPHIC
TRANSMISSION OE
PHOTOGRAPHS
T. THORN E BAKER,
F.C.S., F.R.P.S., A.I.E.E.
NEW YORK
D. VAN NOSTRAND CO.
23 MURRAY AND 27 WARREN 'STREETS
1910
PREFACE
VERY little is known at present about the telegraphy
of pictures, because -the published descriptions of the *
instruments in use have been confined almost entirely
to technical journals. The desire to have news at
the earliest possible moment, and the recent demand
by the public to have the " news in pictures," has
opened up the field for a new science, which is a
peculiar mixture of electricity, optics and photo-
engraving. The telegraphed picture, at first looked
upon as a marvel, now occasions little or no surprise,
which means that it is sufficiently like an ordinary
photograph to pass muster among the other pictures
in the newspaper in which it appears.
During the last two-and-a-half yeajrs, a great deal
of experimental work has been carried out by me for
The Daily Mirror, and it has been very largely
owing to the active interest this journal has shown
in photo-telegraphy that the pioneer work in this
country has been possible. The interest displayed
in the work by the editor, Mr. Alex. Kenealy, has
never failed, and to his encouragement and enter-
prise the present position of this new branch of
telegraphic work is largely due.
210719
vi PREFACE
The descriptions given in the book of the systems
in use to-day will, I hope, make quite clear to the
reader " how it is done." Though certain portions
of the matter are intended for those already con-
versant with the general principles of electricity, the
bulk of the book has been written as simply as
possible, and if the said portions are just passed over
by the non-technical reader, I think the rest will be
of interest to him.
At the time of going to press, preparations are
being made for an endeavour to transmit photographs
by wireless telegraphy across the Wash, the Post-
master-General having courteously allowed me the
use of the experimental wireless stations at Hun-
stanton and Skegness. The last chapter, therefore,
dealing with wireless work, will make the reader
acquainted with the latest phase of photo-telegraphic
work.
T. THORNE BAKER
15, GROSVENOR GARDENS,
CRICKLEWOOD, N.W.,
March, 1910.
CONTENTS
PAGE
PREFACE . . . . . . . . . . v
LIST OF ILLUSTRATIONS . . ix
CHAPTER I.
Attempts at the Solution of the Telegraphic Transmission of
Photographs and Pictures p. i
CHAPTER II.
Professor Korn's Selenium Process Early Work with his
Original Receiver The String Galvanometer Syn-
chronism First Experiments The Early History of
Commercial Photo-Telegraphy . . . . p. 2,2,
CHAPTER III.
The Korn Telautograph Principles of Working Advantages
over Selenium Early Work with Line Pictures Experi-
ments with Telephone and Telegraph Cables Recent
Progress with the Telautograph . . . . p. 61
CHAPTER IV.
The Thorne- Baker System Differences between the Telectro-
graph and Earlier Chemical Systems Electrolytic
Records of Currents Transmitted through Long Cables
The Thome-Baker Line-balance Work with the Electro-
lytic Telectrograph p. 88
viii CONTENTS
CHAPTER V.
Considerations of the Telephone and Telegraph Lines and
their Influence on Photo-Telegraphy . . . p. 108
CHAPTER VI.
The Telestereograph of M. Belin The Early Work of Belin
Changes in his System Recent Experiments . p. 116
CHAPTER VII.
The Transmission of Photographs and Pictures by Wireless
Telegraphy p. 127
INDEX 143
LIST OF ILLUSTRATIONS
FULL PAGE ILLUSTRATIONS.
A part of the Daily Mirror Installation, showing the
Korn Telautograph and the Thorne- Baker Telec-
trograph ....... Frontispiece
Receiving a photograph on the Telectrograph . Opposite p. 100
ILLUSTRATIONS IN TEXT.
FIG. PAGE
1. Diagram of Bakewell's instrument .... 3
2. Section of a film, showing silver deposit ... 13
3. Bernochi's wireless apparatus ..... 15
4. Polarisation receiver of Rignoux and Fournier . . 17
5. Diagram of selenium cell 22
6. Photograph of selenium cell 23
7. Diagram of Korn's selenium transmitter ... 24
8. Inertia curve of selenium 27
9. Curve showing effect of light on selenium ... 28
10. Korn's compensating bridge 29
11. Curve showing compensation of inertia ... 30
12. Curve showing compensation of inertia ... 30
13. Curve showing over-compensation . . . 31
14. Section of Korn's galvanometer . -33
15. Section of interior of galvanometer . . -34
1 6. Korn's receiving apparatus . . . . -37
17. Photograph of a galvanometer as used by Prof. Korn 38
1 8. Diagram showing synchronising arrangement . . 39
19. Diagram of friction clutch ... 41
20. Photograph of the frequency meter . -43
21. Diagram of switchboard connections . . 44
22. Prof. Korn at the telephone, when awaiting the first
picture from Paris in 1907 . . 4 6
LIST OF ILLUSTRATIONS
23. Curve of selenium cell . 47
24. One of the first photographs wired by Korn's com-
pensated selenium machines ... -49
25. Photograph of King Edward, wired to London
November yth, 1907 . . 50
26. Photograph showing induction effects . . 53
27. Example of a news photograph sent from Paris . 55
28. Diagram illustrating principle of the telautograph . 62
29. Korn's telautograph transmitter . . 63
30. Diagram of stylus holder 65
31. Diagram of Korn telautograph ... -67
32. Diagram of synchronising arrangement ... 70
33. Wiring of reverser 71
34. Reception to Sven Hedin, wired from Paris to
London by Telautograph 75
35. Example of Fashion Plate wired by the Korn
Telautograph 77
36. Diagram showing duplex transmission . . -79
37. Line drawing transmitted by Telautograph . . 81
38. Example of line sketch from photograph, wired by
the Korn Telautograph from Paris to London . 83
39. Damping of oscillograph string 85
40. Example of half-tone photograph transmitted from
Berlin to Paris by Telautograph .... 86
41. Telectrograph tracing stylus 91
42. Curve showing charge and discharge of a cable . 92
43. Diagram of connections of line balancer ... 93
44. Photograph showing the balancing effect of the
Telectrograph arrangement 94
45. Portrait of first lady councillor of Liverpool. Wired
by the Telectrograph from Manchester to
London 98
46. Portrait of Mr. Howarth, telegraphed from Man-
chester to London by the Thorne- Baker Telectro-
graph . ioo
47. Half-tone single line negative image, as ordinarily
used for the Telectrograph . . . . .102
48. Finish of the St. Leger, wired by the Telectrograph . 104
LIST OF ILLUSTRATIONS xi
49. M. Riolle, Public Prosecutor in the Steinheil case ;
wired from Paris to London by the Thorne- Baker
Telectrograph . . 106
50. News photograph wired from Manchester to London
of a railway accident at Staly bridge . . .107
51. Apparatus used to record oscillograph work . . 109
52. Oscillograph record of half-tone image with no
capacity on line . ... no
53. The same with capacity, showing the elongation and
widening of the " teeth " . . . . no
54. Section of a relief photographic film . . . .117
55. Diagram of Belin's transmitter . . . . .118
56. Photograph transmitted by M. Belin's Telestereo-
graph, over an artificial line ..... 124
57. Belin's apparatus for telegraphing line pictures . 125
58. Diagram of wireless apparatus 130
59. Diagram of Marconi's Electromagnetic Detector . 132
60. Arrangement first used by the Author for the wireless
transmission of pictures . . . . . 133
61. Sketch of head and shoulders of a lady. Trans-
mitted by wireless 135
62. Diagram of the author's decoherer .... 136
63. Quartz string and selenium cell arranged for re-
ceiving and transforming up electrical oscillations . 138
64. Sketch of the King transmitted by the author's
wireless apparatus ....... 139
THE TELEGRAPHIC
TRANSMISSION OF PHOTOGRAPHS
CHAPTER I.
ATTEMPTS AT THE SOLUTION OF THE TELE-
GRAPHIC TRANSMISSION OF PHOTOGRAPHS
AND PICTURES.
THE problem of transmitting a sketch or photo-
graph over a distance by means of electricity has
occupied the minds of many engineers and scientists
for the past sixty years, but it has been up to the
present time a singularly ungrateful task, owing to
the lack of possible application. The tendency for
modern journals to be illustrated with photographs
has very greatly widened the scope for an instru-
ment by which they can be " wired/' and it is pro-
bably for this reason that so much attention has of
late been devoted to this new science.
It seems difficult on first thought to conceive how
a picture can be telegraphed. But a picture, just
like a written message, can be split up into com-
ponent parts ; the letters forming a 'word have a
distinct meaning when seen assembled together in
P.T. B
2 PHOTO-TELEGRAPHY
proper order, while the dots and dashes forming a
letter, according to the Morse code, possess simi-
larly an intelligent meaning when grouped together
in correct order ; by building up a complete picture
with dots or small areas of varying depth, size,
or density we can produce a picture in a strictly
comparable manner. One ingenious attempt at the
solution of photo -telegraphy as ingenious as it is
impracticable has been to divide up a picture into
thousands of small parts, representing each by a
certain letter of the alphabet, according to its den-
sity ; thus a light part might be called C or D, a
dark part Y or Z, and so on. The letters are tele-
graphed to an operator, who forms a fresh picture
by building it up with small " parts/' whose
densities are in accordance with the respective
letters. Such a system is indeed possible, but would
require a very great amount of time. It is the
minutes and seconds which have to be saved in
telegraphing a picture especially in these days of
rapid railway transit, where photographic plates can
be sent to the newspaper office in a few hours,
so that only very late events are telegraphed.
This book is not intended to be historical, and I
shall therefore refer only to such early processes as
have a direct bearing upon the work that is being
done to-day. Of early attempts at the transmission
of pictures, the Bakewell system deserves particular
notice, since upon it is based one of the three
BAKEWELL'S PROCESS 3
most successful modern methods of transmission.
Bakewell's machine, which created some attention
as far back as 1847, consisted of two synchronously
revolving metal cylinders one at each end of the
telegraph lines, over each of which a metal style
traced a spiral path (in the manner of the modern
phonograph). Upon one cylinder was placed a
sheet of tinfoil with the sketch drawn in ink made
with shellac, and on the receiving drum was placed
a sheet of paper prepared chemically, so that on
Battery
FIG. i.
passing an electric current through it a chemical
mark or stain was made. It appeared as seen in
Fig. i in its simplest form. A and B represent
the two cylinders, tracing over which are shown
two styles. A battery is in the circuit. It will
be readily seen that when a line in the sketch
which consists of shellac, comes under the style of
A, the current flowing through the circuit will be
broken, whereas when the bare tinfoil lies between
style and cylinder the current will flow.
This current therefore flows intermittently
through the chemically -prepared paper attached to
the drum /?, and when it flows, it causes a chemical
4 PHOTO-TELEGRAPHY
mark on the paper. Hence, when the style has
traced over the entire length of the sketch at A, the
latter will be reproduced (negatively) at B. By
suitable means it can, of course, be received posi-
tively if desired.
Such is the system which is now over sixty years
old, and many trials were made with it to telegraph
writing over distances ; here, however, the diffi-
culties met with in long cables were at once felt ;
attempts were actually made at one time in France
to use such a system commercially, but they were
soon abandoned.
Thence onwards continuous attempts were made
to solve the problem of transmitting sketches,
pictures, and photographs ; a long list of names of
these early workers might be given. But we may
well confine our attention at present to two men,
Amstutz and Shelford Bidwell, as the ideas of these
men were actually the germs of two important pro-
cesses which have now given most satisfactory
results. The latter made use of the newly dis-
covered sensitiveness to light of the metal selenium,
the former of the possibility to use the relief in a
certain form of photographic image to vary the
strength of the electric current.
On the lines followed by Bidwell, Ayrton and
Perry also made experiments, both therefore utilis-
ing selenium at the sending station. Let us suppose
that a portrait is to-be telegraphed from this station
THE SELENIUM CELL 5
to a distant receiving station. t The portrait is pro-
jected on to a screen, where light and shade and
varying tones are produced. Now suppose this
screen divided up into a thousand square sections,
each one the size of a selenium " cell," the cell
being an arrangement made with selenium, which
varies in its electrical resistance according to the
strength of the light illuminating it. This cell is
held in one section of the bright image on the
screen, then in the next, then in the next, and so
on, until finally it has been held in the whole thou-
sand sections. But each section is of a different
brightness, according to what portion of the image
is projected upon it. In each section, therefore,
that the cell was held, its electrical resistance
varied.
Now imagine you could record these variations
in resistance on a similar screen at the receiving
station. When the selenium cell was held over
section i of the image of the screen, its resistance
was, let us say, r\ ; using a battery of 100 volts,
and neglecting the resistance of any connecting
lines, the current at the receiving station would be
. Let this regulate, in any imaginable way,
r\
the strength of an electric light, which is shining
on a similar screen at the receiving station, on the
screen being placed a sheet of sensitive photo-
graphic paper. Next let the selenium cell be held
6 PHOfO-TELEGRAPHY
in the section 2, so that a slightly different part
of the image falls upon it, the resistance changing
to r 2 , and the current at the receiving station to
- ; simultaneously let the electric lamp (whose
Y i
brilliance has of course changed in the proportion
of r\ to r 2 ), shine on section 2 of the receiving
screen. If you can imagine this procedure to be
carried out over the whole photograph at the send-
ing station, the ever-varying electric lamp being
shone on always corresponding sections of the
photographic paper at the receiving station, the
movements being in all cases synchronous, you will
be able to see that on developing the sheet of papei
a photograph would be obtained, consisting of a
thousand square patches of different intensity,
which, examined from a distance, would give a
representation of the original image projected on
the screen. Such a process would in practice be
both absurd and impossible, but it enables one to
form some conception of the idea of Bidwell and
Ayrton and Perry.
The image to be telegraphed could quite easily
be a photograph printed on a transparent material,
such as celluloid, and this print fixed to a revolv-
ing glass cylinder, inside which was fixed an
electric lamp, whose rays were concentrated so as
to pass through one spot on the cylinder to a fixed
selenium cell. On then revolving the cylinder
SELENIUM DIFFICULTIES 7
and letting it also rise spirally, the pencil of light
would traverse different consecutive parts of the
picture, and the light falling on the selenium would,
of course, vary in strict accordance. Such a
method is practically similar to that actually used
by Professor Korn, as will be seen on reading the
next chapter.
Then, again, the current sent to the receiving
station, which would depend at each instant on the
density of the particular piece of photograph
through which the pencil of light was passing, could
be utilised to open or close a shutter through which
another pencil of light could be admitted to a sen-
sitive photographic film. Suppose this film on a
cylinder revolving in a precisely similar fashion to
the transmitting cylinder, and you have what prac-
tically amounts to Professor Korn's receiver.
The great practical difficulty arose, however,
from the fact that selenium, unlike the feminine
mind, could not change rapidly enough ; there are
an immense number of different tones in one small
strip of a photograph, and the constant changes in
illumination were not at all well responded to by
the selenium cell . The practical application of the
method was destined to await Professor Korn's re-
markably ingenious work on the compensation of
the " lag " in selenium cells, which only became
possible after much very ingenious mathematical
and experimental work, Korn is a master mathe-
8 PHOTO-TELEGRAPHY
matician, and photo -telegraphy is one instance
where somewhat abstruse calculations on paper
turned out to be in perfect harmony with practical
work.
In referring to the methods of Amstutz, I will
quote from an interesting article by Mr. William
Gamble, that appeared twelve years ago in the first
number of Penrose's Pictorial Annual, of which he
is the editor. Briefly, he says, the process is this :
A photograph in relief (prepared in gelatine) is
fixed to something akin to a phonograph cylinder,
so that a stylus travels over its surface, rising and
falling as the picture passes beneath it. Instead
of producing sound, like the phonograph, it is made
to vary the strength of an electric current, which
passes over a telegraph wire and actuates a similar
stylus at the other end, which, bearing on a plate
bent round a revolving cylinder, cuts a reproduc-
tion of the original, but in a series of parallel lines
(the successive " turns " of the cylinders) which
gives the effect of a half-tone block. The stylus is
sharpened like a graving tool, V-shaped, so that
as it cuts deeper it cuts wider, and in printing
produces darker or wider lines,
Amstutz, in a lengthy letter which the editor of
the Annual publishes, describes a method in which
a photographic print is made on a metallic sheet,
the half-tone of the photograph being broken up
into parallel lines, " the photo -message being re-
AMSTUTZ AND BELIN g
ceived at the distant station in an engraved manner
ready for printing."
" Theoretically/' he says, " the half-tone system
encounters no difficulties whatever. From a prac-
tical point it is not available for commercial work."
He describes the troubles that would arise from
interference effects, owing to the lack of correspon-
dence that there would be between the mesh of the
half-tone screen and the path travelled by the stylus
over the cylinder, and claims that by using the
single-line pictures referred to these troubles could
be avoided.
In all the half-tone photo -telegraphic work
single -line pictures are solely used, but at present
no satisfactory method has been obtained of
engraving the block direct during the reception.
Amstutz's idea of using a photographic image in
relief, and making the actual relief mechanically
vary an electrical resistance, has been successfully
followed up by a French inventor named Belin, but
he again cannot obtain direct engraving at the
receiving end.
Direct photo - engraving by telegraphy may
"come" some day, but not until that much desired
thing has been discovered, the variable relay. The
resistance of a telephone line two hundred miles
long may be, perhaps, 2,000 ohms. We cannot
employ very high voltages, 100 volts being con-
sidered very high ; if we divide i oo by 2,000, we
io PHOTO-TELEGRAPHY
get the maximum amount of current that could be
obtained at the receiving station one -twentieth of
an ampere ; with '05 ampere and only therefore
5 watts, it would be almost impossible to actuate
a graving tool, even to cut into some soft composi-
tion. Block -making is so rapidly done in a
modern illustrated newspaper office that such a
method is not now worth following up.
Turning next to Caselli's pan-telegraph, we find
him employing a sheet of metal with a sketch or
writing drawn upon it in insulating ink ; the sketch
on metal was stretched over a curved copper plate,
and a similar curved plate was placed at the receiv-
ing station, a sheet of paper moistened with
potassium ferricyanide solution being stretched
over it. The plates were electrically rocked,
synchronism being obtained by means of a pen-
dulum. A metal stylus traced over the sketch at
one end and over the paper at the other, the circuit
being completed through the metal plates. At the
end of each " rock " the paper and sketch were
shifted laterally, so that in each case the stylus
travelled over a line parallel to the last line traced.
When the sending style touched the metal the
current flowed and the ferricyanide was decom-
posed, a blue mark being produced. Some excel-
lent transmissions of writing, etc., were obtained
in this way at a comparatively high rate of speed.
The same system was employed by the French tele-
THE TELEWRITER n
graph engineer, Meyer, except that he used syn-
chronously revolving cylinders in place of the
curved metal plates.
Although the transmission of writing cannot be
classed with the telegraphy of photographs, it will
be, nevertheless, of interest to describe the tele-
writer, which gives a facsimile reproduction at the
receiving station of anything written or sketched
at the sending station. In writing any letter on
paper, the movement of the pen can always be re-
solved into horizontal and vertical components ;
by making these resolved movements mechanically
vary two resistances, currents of two corresponding
strengths can be transmitted to a receiving instru-
ment ; but three lines are necessary, or two lines
and an earth. The two currents when received are
used to actuate a V-shaped nib filled with ink, both
vertically and horizontally, the resultant move-
ment causing the nib to trace over the paper a
replica of whatever the transmitter draws with his
mechanical " pen." In the telautograph of Grzanna,
the two currents corresponding to the vertical and
horizontal movements of the transmitting pen are
made to actuate a mirror galvanometer, the mirror
of which can turn about two axes, so that a spot
of light traces the letters or sketch over a sheet
of photographic paper.
^These methods are only suitable for transmitting
sketches or designs that are drawn at the actual
12 PHOTO-TELEGRAPHY
time of transmission. A cartoon was in one
instance drawn by Mr. W. K. Haselden in Man-
chester and sent by him to the London office of
the Daily Mirror, but it was not so satisfactory as
the same sketch would have been had it been
photographed and then telegraphed to London ;
the pencil of the transmitter requires some prac-
tice to use it with comfort.
A method more recently worked out for the
transmission of photographs is that of Charbonelle,
a French postal engineer, in which once again the
Caselli transmitter is employed, and a series of short
currents are transmitted which correspond to the
interruptions caused by the insulating lines of a
sketch or single -line screen half-tone photograph.
He has also endeavoured to transmit by a method
that has been put to the test by almost every
engineer who has paid any attention to the problem
of photo -telegraphy, namely, by causing the deposit
of silver (or other substance) in the image of a
photographic film to act as the means of varying
the current transmitted'. This was very carefully
investigated by the author in 1907, about a year
before the publication of Charbonelle's patent, but
although results of a kind were obtained, the idea
was abandoned owing to certain fundamental diffi-
culties which will probably never be overcome.
In Fig. 2 is seen a diagrammatic representation
of a transverse section of the film of an ordinary
CONDUCTIVITY OF FILMS 13
photographic negative. Let S be a stylus travel-
ling over the film ; now consider any points
PQR, it being supposed that the film has been
coated 'on metal foil instead of glass or celluloid.
If one terminal of a battery be connected to S, the
other to the metal foil, current will flow from S to
P, in one instance the reduced silver grains form-
ing the image being represented by dots. Now
suppose the stylus to be at S', where, owing to a
light part of the picture, there is much less deposit
of silver. Assuming trie film to be of gelatine (in
a moist condition),
less current will , s - s '
ir ,>,
flow from S' to R **p~'~"'' : ' "'-' :: ?" ' : '^
than from S to "p q ^
P, as between S FIG. 2.
and P there are
many more granules of silver to render the film
more conductive. Hence, if the photograph be
rotated on a cylinder, and the stylus trace a spiral
path over its surface, the current flowing through it
to a receiver should vary in accordance with the
depth of silver deposit. I also tried using a relief
carbon image on copper foil, the gelatine being
saturated with a badly conducting medium, so that
the current passing from style to copper base would
vary inversely as the thickness of the film ; some
fair results were obtained in this -way, but the
method would be always very uncertain, as the
14 PHOTO-TELEGRAPHY
current would pass through the film in the line
of least resistance.
Charbonelle's receiver is also one that has been
suggested by some of the earlier workers ; he
passes the received current into a microphone, in
the centre of the diaphragm of which is a hardened
point ; this point of course vibrates in the same
manner as the diaphragm. The microphone is
brought down over the cylinder of the receiving
apparatus until it presses on an outer sheet of paper
wrapped round it ; under this outer paper is, first,
a sheet of carbon paper, and second, another sheet
of plain paper. As the microphone diaphragm
vibrates in response to the interruptions of the
current, so the point digs into the outer paper and
the mechanical pressure causes a carbon mark on
the inner paper. The results are stated to be good,
but the method is not likely to be of use for long
distances.
Berjonneau has worked out a method of trans-
mitting half-tone photographs made with a single -
line screen, the receiver containing a minute shutter
which cuts off or allows to pass the rays from a lamp
concentrated on a revolving sensitive film. I Have
seen a promising result obtained with his appa-
ratus,* but detailed particulars of his system are
not yet available. He has, however, made trans-
missions over a telegraph line from Paris to Eng-
* Shown at Soc. Ing. Civ., Paris.
A WIRELESS METHOD 15
hien " in four minutes seven seconds," according
to a newspaper report, " and the reproduction at
EngHien did not show any signs of lines, and might
have been made in the studio of a photographer. 1 '
An ingenious idea for transmission without wires
deserves mention here, and has been patented by
the inventor, Francesco de' Bernochi, of Turin. The
invention can never be of much practical value, and
is, in fact, a retrograde one, carrying us back to the
early experiments in wireless telephony by means
FIG. 3.
of light waves. The apparatus can be followed by
glancing at Fig. 3. Here Ci is a glass cylinder
with a transparent photographic film wrapped round
it, and light from the lamp L, after passing through
a small portion of it, is reflected by a prism on to
a selenium cell SS. This is in series with a battery
and the primary of a form of induction coil. As
light of different intensities falls on the selenium
cell, whose resistance alters in proportion, current
is induced in the secondary of the coil and influ-
ences an arc lamp, on whose circuit it is shunted ;
16 PHOTO-TELEGRAPHY
this arc, the poles of which are represented in the
diagram by PP, is placed at the focus of a parabolic
reflector RI, and its rays are therefore reflected as
a parallel beam to the receiving reflector R 2 . At
the focus of this second reflector is a selenium cell
Z, whose resistance is altered by the light falling
upon it from the reflector. This cell is in series
with a battery and mirror galvanometer, light from
a lamp N being reflected by the mirror on to a
graduated aperture H ; the collected light is
focussed upon a photographic film attached to the
drum 2, which revolves synchronously with the
transmitting cylinder Ci.
The idea is an ingenious one, and might be made
to work in practice over distances of a few hundred
yards, but not more. A suggestion was made on
somewhat similar lines to these to the author by
Mr. Sharman, in reference to Korn's selenium
machines, but for the purposes of wireless tele-
graphy the fluctuations in the resistance of the
selenium would be used to influence the undamped
oscillations given out by a singing arc, and a suit-
able receiver would record these fluctuations
photographically .
One other possible means of receiving from any
form of transmitter over short distances deserves
reference, inasmuch as it has recently received the
attention of Rignoux and Fournier for their pro-
posed television apparatus. It is well known that
POLARISING RECEIVER 17
if ju, be the refractive index of a substance, and $
the angle of polarisation for that substance, the
relation holds good.
fji = tan (/>.
If a liquid substance contained in a tube BC
(Fig. 4) be subjected to a field produced by a coil
through which current is passing, its refractive
index will be changed ; hence </> will be changed
also. If rays of monochromatic light from a
lamp L pass through one nichol prism NI, then
<D
FIG. 4.
through the tube BC of liquid (carbon disulphide),
afterwards passing through the analysing prism N 2
and thence to a photographic film attached to a
receiving drum D, the nichols being set at the polar-
ising angle, no light would reach the film unless a
current passed through the coil round BC. The
terminals of such a coil would be connected to the
line AA, either directly or through a relay, and
hence the film on D would record the impulses sent
through the coil. The sensitiveness of such an
apparatus would be very small unless a relay were
employed, and this would at once put a limit on
the speed of working, which wouid seriously
hamper its utility.
P.T. c
18 PHOTO-TELEGRAPHY
The commercial utility of photo -telegraphy only
commenced after the adoption of Professor Korn's
instruments by the Daily Mirror. Although his
selenium machines were installed in Berlin and
Paris at the same time, the Daily Mirror in
London may be said to be the only journal that
has utilised them, or any subsequent machine,
in -a really commercial way. Two of Korn's
selenium machines were installed in Stockholm
and Copenhagen in 1908, and some trans-
missions have been made by the newspapers which
took up his system, but ever since their instal-
lation of the selenium instrument in November,
1907, the Daily Mirror has systematically carried
out transmissions and has persistently endeavoured
to develop tHe really practical side. The large
amount of experimental work that I have carried
out has been done entirely for the Daily Mirror,
and the present state of efficiency of this new
science is very largely due to the substantial help
they have given to it.
This chapter has been written from a more or less
historical standpoint, and it may therefore be said
that the commercial or practical history commenced
in 1907 with the use of Korn's selenium machines.
The progress that has been made during the last
two and a -half years has been very considerable,
and has been almost entirely due to paying the
closest attention to small details. The mechanical
FUTURE PROSPECTS ig
parts of the various instruments have been made
with greater precision, the physical theory of the
selenium cell has been exhaustively worked out by
Korn, who has also made a great deal of progress
in determining the best form of string for the
galvanometers used in photographic receivers. M.
Chatenet, of L' Illustration, Paris, has done much
valuable work in connection with the preparation
of the line photographs for transmission, the
importance of which will be seen later.
History does not dip into the future, fortunately
for the historian, but it is quite clear by now that
the telegraphy of photographs has a commercial
value, and that this value will rapidly increase with
the demands for pictures made on modern journa-
lism. What other uses it will be put to remain to
be seen, but there are many possibilities. As
regards distance, where the cable renders trans-
mission too slow, "wireless" may solve the
problem, but that also remains to be seen.
Before closing this chapter, I should like to refer
once more to Mr. Gamble's article in Penrose's Pic-
torial Annual, which it is interesting to recall to-
day, since his predictions have been so well ful-
filled.
" But suppose," he says, speaking of illustrated
journalism, " it were possible to transmit the picture
over the wires with the same facility as we now
transmit the words, and suppose that the same
c 2
20 PHOTO-TELEGRAPHY
electric current rendered a transcript of the picture
in a form suited for immediately using or convert-
ing into a printing surface, what a revolution it
would effect in the methods of giving news to the
public, ... of whose craving for illustrations
editors and publishers are fully conscious. ' Quite
so,' says the practical editor, l but will such a thing
ever be possible ? I doubt it/
" Well, just to call to mind what electricity has
already given us besides telegraphy. By means of
this wonderfully potent power we transmit sound,
light, heat, and motive energy. Its latest and
perhaps most marvellous development is the utilisa-
tion of the so-called * X-rays ' to enable us to probe
the mysteries of our anatomy and search for things
hidden from mortal eye. Surely it is but a little
step to annihilate the limitations of human vision
and provide us with a means of seeing things from
afar. Undoubtedly this will be the next wonder
that electricity has in store for us."
Then, after describing Bain's chemical tele-
graph, in which at the transmitting station a metal
brush passed over large metal type letters and
closed a circuit which chemically reproduced the
letters at the receiving end, he says :
" I mention the foregoing chemical process,
because I think it will suggest to photographic
experimentalists a likely method of transmitting
pictorial records. For the letters of Bain's instru-
SOME' PREDICTIONS 21
ment substitute a half-tone enamel print on copper
showing alternate bare and covered parts, and
the point then is to find a sufficiently sensitive
transmitter."
The receiver is the part that remained to be made
sufficiently sensitive, and I cannot help thinking the
word " transmitter " was used for " receiver " by
a slip. How this sensitiveness has been obtained
will be explained in the chapter dealing with the
telectrograph.
\
CHAPTER II.
PROFESSOR KORN'S SELENIUM PROCESS EARLY
WORK WITH HIS ORIGINAL RECEIVER THE
STRING GALVANOMETER SYNCHRONISM -
FIRST EXPERIMENTS THE EARLY HISTORY
OF COMMERCIAL PHOTO -TELEGRAPHY.
THE metal selenium is, in its crystalline state,
very sensitive to light. It has been utilised in
many instances of light telephony, from which it is
obvious that it is sen-
sible of extremely rapid
changes in the illumi-
nation.
The selenium cell,
FIG. 5. so-called, takes the
form shown in Fig. 5 ; on a thin rectangular slab of
slate, steatite, or some other suitable material, two
coils of platinum wire are wound, one coil being
wound " inside " the other, so that no turn touches
another turn ; thus, in the figure, turns i, 3, 5, 7,
9 ... belong to one coil, while turns 2, 4, 6, 8,
10 . . . belong to the other. We now fill in the
spaces between the turns with selenium, so that if
the resistance between turns I and 2 were R, and
there were n turns in each of the coils, the total
THE SELENIUM CELL 23
resistance of the " cell " would be approximately
TD
-, assuming the number of turns very great and
their distance apart equal. The dimensions of the
FIG. 6.
cells made by Giltay, of Delft; Holland, are about
6-3 x 2*8 cm., and their resistance varies between
very wide limits ; thus one may have a cell whose
resistance is only 20,000 ohms, or one of
R = 250,000 11. It seems to be a general rule that
the greater the resistance of the cell the smaller its
inertia, but it is by no means always the case.
The selenium has to be kept at a definite high
temperature until it assumes the crystalline, slate -
coloured form, when it becomes electrically con-
ductive and sensitive to light. The light is appa-
rently absorbed and made to do wok in lessening
the resistance ; the physical change is not relaxed
PHOTO-TELEGRAPHY
the original state not restored immediately the
action of the light is discontinued ; the return to
normal condition is thus not instantaneous; there is a
lag, whilst over-illumination and excessive illumina-
tion may cause some long-sustained effect which has
been conveniently termed fatigue. In Fig. 6 is seen
an actual photograph of a selenium cell.
SE
FIG. 7.
The difficulties caused by these characteristics of
4^
the selenium cells will be readily understood when
we see how the cells are employed by Korn in his
system. I shall therefore describe the sending
instrument in its simplest form, after which we can
come back again to physical considerations.
The principal portion of the sending apparatus
is shown in Fig. 7. Here the light from a Nernst
lamp N is concentrated by the necessary lens system
KORN'S TRANSMITTER 25
on to the glass cylinder CO', so that the rays cross
at the point A where the pencil meets the first
surface of the cylinder. A transparent photograph
printed on a celluloid or gelatine film is wrapped
round the cylinder, so that at A the light passes
through one small point of it ; it travels thence
into the 45 prism P, by which it is reflected
upwards upon a selenium cell SE. The glass
cylinder is attached to a shaft with a screw thread,
which turns in a fixed threaded collar T, so that
when revolved by a motor it rises and turns spirally.
It is thus seen that the spot of light at A in effect
traces a spiral path over practically the whole
photograph in due course. The intensity of the
light at any instant depends on the density of the
photographic film in the portion traversed at that
instant, so that the light falling upon the selenium
cell is always varying in accordance with the density
of the photograph.
The " point " embraced by the light pencil at A
is in reality about 3X2 mm. in area, hence no
small details can be transmitted as several would
be embraced at once by the beam. This is the
reason why only portraits or very simple subjects
could be transmitted by the selenium machines.*
* More complicated pictures have been transmitted by
Korn's selenium machine by enlarging up the subject and
dividing it into three or four parts, telegraphing each separ-
ately and then joining up the telegraphed components.
26 PHOTO-TELEGRAPHY
The size of the glass cylinders used is 13 cm.
length by 7 cm. diameter, so the picture transmitted
is 22 X 13 cm. The pitch of the thread on the
axle is i mm., so that the cylinder turns 130 times
during a complete transmission ; it revolves once in
5 seconds, hence the time of transmission is just
over i i minutes. Arrangements were provided in
some of the machines to double the pitch of the
axle thread, so that a photograph could be tele-
graphed in under 6 minutes. This, of course,
meant a corresponding sacrifice of detail.
We must now return to the selenium cell and see
how its slowness to respond to the variations in
illumination cast upon it from the prism have been
largely overcome by the ingenious system of " com-
pensation " worked out and patented by Professor
Korn prior to 1907. If a certain amount of light
be falling upon the cell, so that its inertia be over-
come, and its resistance be n, then any increment,
61 in the illumination will give a decrement in the
resistance, in a way connecting the reciprocals of
the resistances r\ and r 2 as follows :
- = + a5I,
r* ri n
or if the increase in illumination be used for only a
short time /,
and /(O converges to i where t = oc F(/) is a
SELENIUM 27
function of the time, and a is (in both cases) a
constant depending on the selenium cell and its
characteristics ; a can, in fact, be termed the
" sensitiveness " of the cell.
Professor Korn has shown that where /3 and ;;/
are inertia constants of the selenium cell the change
in resistance y can be obtained for an increase
in illumination 51 from an equation of the form
current = y = abl.e ~ &
where O < ;;/ < oc ; /3 is the inertia constant and
FIG. 8.
m the exponential inertia ; for photo-telegraphic
work m should be as small as possible, and this is
obtained best by using platinum wire in the
preparation of the cell and very pure selenium ;
m can be made as low as f .
The relation between^ time and current, shown
as an inertia curve, is seen in Fig. 8. In the
figure we see the effect of suddenly illuminat-
ing the cell for a time which, expressed as the
abscissa, goes as far as the vertical dotted line ;
after the time t the illumination is cut off, but the
resistance, instead of increasing again to normal
instantly, takes a considerable time as indicated ;
28
PHOTO-TELEGRAPHY
there is considerable lag, and it may actually take
some seconds before the resistance becomes the
normal for no illumination.
Now let us see what this means in actual photo-
telegraphy. It has been seen that the transparent
photograph revolves in cylindrical form, so that
different consecutive parts of it intercept the light
beam which, after reflexion in the prism, falls on
the cell. Suppose a bright part in the photograph
Y
O I ( ( icrmn u.f t 071
FIG. 9.
is adjacent to a very dark part, the light falling on
the cell is great at the moment the bright part inter-
cepts the light, and is very small immediately after-
wards when the dark part takes its place. The
current passed through the cell should increase with
the bright part and instantly fall again when the
dark part comes ; instead, the lag in the cell inter-
venes, and it only half falls, and thus interferes
fundamentally in the process.
Various means have been tried to counteract the
COMPENSATION METHOD
29
inertia, and to my mind the most successful is the
method Korn has suggested of keeping the cell
always sufficiently illuminated to overcome it.
Thus suppose we represent the effect of light on
resistance by a curve of the form shown in Fig. 9,
the point P gives us the place on the curve after
Receiving
Galvanometer
-/v
FIG. 10.
which for every increment of light 6L the decrease
in resistance in a small time t is dbR. If suffi-
cient light OL be allowed always to fall on the cell
so that the inertia YP is overcome., the effect of
any additional light will be very rapid. The com-
pensation method of Korn gives further a much
brisker action, and the scheme is seen in Fig. 10.
Here the light which has traversed the revolving
photograph falls on the selenium cell S^i. This cell
30 PHOTO-TELEGRAPHY
is placed as one arm of a Wheatstone bridge,
a second cell S^ 2 being placed on the opposite
arm. W is a regulating resistance, and BI and
B 2 two batteries of about 100 volts, BI being
provided with a compensating variable resistance
W 2 . The galvanometer is of the "string" form,
i.e., two fine wires XY move laterally in the field
of a powerful electromagnet, whose pole pieces MM
are tunnelled with a hole. A small piece of
Tim e
FIG. n.
77,
FIG. 12. .
aluminium or magnesium foil is stuck to the wires
in the centre, and this shutter just cuts off the
light which would pass from a Nernst lamp N
through the poles. If current passes through
the wires they are laterally displaced, and
the beam of light can then reach the second
selenium cell S^ 2 . As the current transmitted to
the receiving station passes there into a precisely
similar galvanometer, the circuit is closed.
Now let us see what happens when a bright part
COMPENSATION 31
in the photograph causes light to be cast on the cell
S^i. The equilibrium of the bridge is at once upset,
current therefore passes through XY, the shutter
is displaced, and light falls, a fraction of a second
later, on to S^- We can represent the effect for an
illumination I by the two curves below (Fig. 11)
on opposite sides of the time axis. Add the two
ordinates and you get the " dead beat " curve shown
in Fig. 12. The effect is almost instantaneous, and
when the illumination ceases the current drops at
once to zero. This effect can only be obtained,
77 me
FIG. 13.
needless to say, when the two cells are well
matched ; it is easy to have over -compensation, as
shown in Fig. 13, where the current is brought
below zero, and time is thus lost in regaining a
normal condition.
It is not difficult to show that for good compensa-
tion, assuming the equations of the two cells be
(ii) ^ = 03*!.* -*"'
we must have the condition fulfilled
At
32 PHOTO-TELEGRAPHY
and that for this we must have
ai /3 t = a 2 /3 2 .
Both cells should have m as nearly equal as pos-
sible and very small the principal cell S^i should
have great sensitiveness and small inertia ; the com-
pensating cell Stf 2 should have proportionately small
sensitiveness and large inertia, so that we can fulfil
approximately the condition
d! /3i = a 2 /3 2 .
A rather interesting point is raised by the fact
that, according to Ruhmer, it is possible to sensitise
a selenium cell for a narrow region of the spectrum.
He had utilised cells of different colour sensitive-
ness with a view to duplex wireless telephony, but
it occurred to the author that possibly by colour
sensitising a cell and using light only of the colour
for the particular illumination the inertia might be
less, and possibly the sensitiveness higher ; with a
cell of " dark resistance " /, the maximum useful
v
amount of illumination only lowers this to perhaps
Y
or -, though one can obtain cells with a very large a,
resistance when dark
so that the ratio r =- ^ = 3 is as much
resistance when illumined
as 4 : i or 5 : i. Thus a cell of resistance 250,000
ohms will sometimes become reduced in resistance
to about 60,000 when illuminated with a ^candle-
power lamp held 3 inches away from it. The
THE STRING GALVANOMETER 33
maximum sensitiveness is towards the yellow-
orange portion of the spectrum, but the inertia
appears to be unaffected by the wave-length,
though Korn has patented the method of using a
selected colour. Several experiments were made
in England screening the light with colour filters,
so that light of known wave-lengths
was used for illuminating the cells.
The results of a series of measure-
ments showed that there was no
advantage, the lag being the same
as when ordinary Nernst light was
employed.
Before describing the actual re-
ceiving apparatus of Korn's selen-
ium machines it will be of interest
to see the construction of the gal-
vanometer, to which he has given
so much attention, and which is of
extreme sensitiveness, especially
when of the modified form as used in his later ' ' telauto-
graph " (see next chapter). The field magnets are
powerful, and the pole pieces measure about
5 X ii X 4 cm. These converge nearly to points
in the centres, as shown in Fig. 14. Thus they
nearly touch at AB, only sufficient room being left
for two fine silver wires to move freely between
them. The hole through the poles is* shown in the
diagram, and a sliding tube T fitted with a small
P.T. D
34
PHOTO-TELEGRAPHY
i K
i Adjusting
Screw
M
short focus lens is provided in the hole nearest the
receiving box. The shadow of a magnesium
shutter (described later) attached to the wires can
be sharply focussed upon a diaphragm by sliding
the tube T to the correct position.
A metal collar (indicated by the
dotted circle) is fixed above the
pole-pieces into which the moving
part of the galvanometer is fitted ;
this part is shown separately in
Fig. 15. The outside portion of
this (MN) is a cylindrical tube
which fits into the collar. A sliding
piece S is free to move up and
down inside the tube, and is fitted
with a screw thread, over which a
graduated adjusting nut is placed.
By turning this regulating screw, S
is moved up or down and the
tension on the wires varied. The
wires, about T^oo^h ^ ncn thick, are
attached to two very fine springs (of
FIG. 15.
the same material) fitted to S. The small shutter F,
about 2 X 1*5 mm. in area, and as thin as possible, is
gummed to the wires so that it comes on the optic
axis when the piece is fitted into the magnet collar.
The sliding portion S is insulated from the brass
tube, but is connected with a contact K. This con-
tact and another metal button C fit against two
THE STRING GALVANOMETER 35
corresponding contacts in the field magnet collar,
which are in turn connected with the sliding
contacts of the resistances already described.
The weight of the " moving part " of the galva-
nometer is almost negligible, its moment of inertia
extremely small, and with the length of wires used
a period of swing as small as y^Jo^h of a second can
be obtained. The current flows in at C and
traverses the fine wires upwards from bottom to
top, leaving them at K. The field due to each is
thus similar, hence their displacement is lateral, and
is approximately equal to
C (_ \ >< constant of galvanometer.
\?i r 2 /
We may regard the wires as elastic substances
stretched across the apparatus, where the dis-
placement D can be represented by f(e), or some
function of the elasticity ; the wires can be set in
vibration, and if one impulse be given by passing
a sudden short period current through the wires,
when displaced thereby through a distance D they
have sufficient potential energy to cause them to
swing back past the position of rest through a
distance slightly smaller than D in the same
manner as a pendulum. This is clearly shown by
the photographic records (p. no) obtained of the
movements of the shutter F recorded under various
circumstances on a moving photographic film.
This period can be made shorter by using shorter
D 2
36 PHOTO-TELEGRAPHY
" strings " or wires., but as there is a practical
limit to their fineness, we must make the factor e
increase by the strings becoming shorter ; hence the
current necessary to displace them an equal amount
becomes greater, and where selenium is used its
resistance is so high that a limit is immediately
set to the length of strings practicable. The
magnetic field may of course be increased when the
galvanometer constant K in the expression
D = CK ( ) becomes greater. The Einthoven
\r\ r*J
galvanometer, of which Korn's apparatus is a
special form, is often provided with a far greater
field than he employs.
Once in each revolution of the receiving drum
there is a distinct kick in the galvanometer, as for
the synchronising of the sending and receiving
apparatus it is necessary, as will be seen later, to
cut the current out of the galvanometer circuit and
switch it into the synchronising gear. This kick,
due to a capacity discharge front the line, was to
some extent overcome by Korn by shunting a small
resistance across the galvanometer at the terminals
K, C. To facilitate its regulation I replaced this
fixed resistance by a regulating shunt resistance of
o to 50 ohms, but it was ultimately found that the
kick could be best avoided by very careful adjust-
ment of the position of the fleeting contact through
which the synchronising current passed.
KORN'S SELENIUM RECEIVER
37
The shadow of the galvanometer foil is cast
upon a triangular aperture in a diaphragm E
(Fig. 1 6), being magnified up a good many
times by the lens T which is fitted into one pole
of the electro -magnet. This shadow prevents
the light from the lamp N reaching the small
lens O which concentrates a real image of the
aperture (when illuminated) upon the photo-
graphic film ; this revolves on the drum D, the
*o
FIG. 16.
drum being fitted into a small light-tight wooden
box. Now if the shutter is displaced, the shadow
moves to one side, and light immediately passes
through the aperture at E and exposes the film.
The more the shadow moves towards the base of
the triangular hole, the greater is the light which
reaches the film ; by using a triangular instead of a
square hole the effect of movement of the shutter
on the light transmitted to the film is obviously
amplified, and this amplification* is necessary
because the ratio of illumination to resistance of
38 PHOTO-TELEGRAPHY
the selenium in the sending apparatus is not con-
stant, but decreases as the illumination increases.
The angle at the apex of the triangle has some-
FIG. 17. Photograph of galvanometer as used
by Prof. Korn.
times to be altered to suit a particular cell, but is
usually about 50 to 60. The shutter, and hence
the shadow on E, is constantly moving more or less
towards the base of the triangle according to the
strength of the current and therefore to the density
SYNCHRONISING
39
of the photograph being transmitted. The area
of the picture received is one quarter that of the
film used in transmission.
The method of synchronising the sending and
receiving cylinders now requires explanation. A
small error in synchronisation will cause distortion
of the picture received, and great care is required
Line
To Galvanometer
To Battery
FlG. 18.
to ensure its accurate adjustment. In Fig. 18
let us suppose that C is the cylinder of the trans-
mitting apparatus, and D the receiving drum.
There is a projecting pin on the bottom of the
transmitting cylinder which once in each revolu-
tion strikes against a contact spring, throwing
it away from contact with P and into contact
with Q. When the spring is in* contact with
p_during practically the whole revolution the
40 PHOTO-TELEGRAPHY
selenium circuit flows through the line to the
receiver. When it is displaced and connects with
Q, the current from the battery has merely to pass
through a small fixed resistance, about one -tenth
that of the selenium, so that the current is some ten
times as great. As soon as the cylinder has turned
a little more,, the spring returns into contact with
P again.
Now at the receiving machine we have a similar
pin which throws over a spring N from contact with
R into contact with S. Whereas R leads to the
galvanometer, S leads to one coil of a relay as
shown, the other coil of the relay being con-
nected with the other unit of the line, together with
the other end of the galvanometer.
What happens then is that every time the pin on
the sending cylinder throws the spring against
the contact Q, a strong current is transmitted
through the line. If at that instant the corre-
sponding spring N of the receiver be also thrown
against S, the current received passes into the
relay instead of into the string galvanometer.
By making the drum D turn quicker than the
cylinder C it will obviously reach the end of its
revolution first. It is then suddenly stopped by
the check T, which strikes against a movable
steel check F. When the slower turning send-
ing cylinder has finished its revolution, the
strong current is sent, as we have seen, into
SYNCHRONISING MECHANISM
the relay, exciting the coils and causing the
small magnetised armature to be attracted to-
wards the left side in the diagram. The pla-
tinum contacts XX then touch, and current from
the local battery passes through the magnet Z.
This attracts the armature H, so that the check turns
about the fulcrum F into a position such that T
is free to move and the drum consequently again
starts running.
The motive me-
chanism driving the
drum cannot of
course stop and
start abruptly at the
end of each revolu-
tion, a friction
clutch is therefore
u
provided, as shown
in the next diagram (Fig. 19). The shaft is
cut through and two parallel faces FF fitted,
springs SS being attached to the lower one which
grip the upper one. When the motion of the
cylinder is checked, the two faces turn one against
the other. The springs are fixed to a collar C
which can be screwed over the threaded shaft,
K being a lock nut. The tension of the friction
clutch can thus be regulated.
The transmitting cylinder is, as 'already stated,
revolved at about the rate of one revolution in five
%
m
V
%
1
%
^
%
H
F
y
v.
Fm
\
(
I
1
n
FlG -
42 PHOTO-TELEGRAPHY
seconds, or in reality at about T 9 o 9 oths of this speed ; as
the receiving drum must revolve quicker, in order
to be stopped and then restarted by the synchronism
signal of the transmitter after each complete revolu-
tion, it is run at about xui tns f the speed. There is
thus a difference of 2 per cent, in the rates of the
two, which means an unavoidable elongation of the
received image.
The regulation of the motors is carried out by
means of regulating resistances and frequency
metres. The motor acts to a small extent as a
dynamo, as two sections of the armature are con-
nected to slip rings with brushes fitted, so that an
alternating current is derived from them. This
alternating current is supplied to an electro-
magnet, whose polarity at one pole -piece therefore
changes twice in each revolution of the armature.
A row of tuned steel magnetised springs is fixed
in front of the pole -piece, fixed at the base and free
to vibrate vertically. These springs are thus
attracted and repulsed at each revolution of the
motor, and if a certain spring among them be cut to
such a length that its period is equal to the period of
the alternating current, it will vibrate very freely,
while other springs not in tune will not vibrate at all .
Now several such springs, so cut that their
periods range from 97 per second to 103 per
second, are fixed at their lower ends in front of the
pole -piece pf the electro -magnet. By means of the
THE FREQUENCY METER 43
regulating switch of the motor an ordinary
variable resistance in series with the field magnets
the motor can be speeded up until, say, the spring
labelled 99 vibrates freely. The motor is then
revolving % 9 times a second, or just under 3,000
FIG. 20.
times per minute. This is the condition for the
motor of the sending apparatus. The face of the
meter is shown in Fig. 20.
Similarly at the receiving station the operator
runs his motor at just over 3,000 revolutions per
minute. Each motor is geared doWh with a worm
drive in oil, which has to work very sweetly in order
44
PHOTO-TELEGRAPHY
to prevent vibration. In many later models of
photo - telegraphic apparatus the motors are
mounted on separate stands and connected to the
driving gear by flexible shafting.
The relay used by Professor Korn for utilising
the synchronising current to close the magnetic
FIG. 21.
check release circuit is a Siemens & Halske polar-
ised relay. A polarised relay is not necessary
unless it be sufficiently sensitive to work with
a current equal in intensity to the line current for
the galvanometer. The Siemens & Halske relay
can be rendered more or less sensitive at will by
regulating the distance of one magnet from the
armature it has to attract, keeping the other
magnet fixed.
THE SWITCH-BOARD 45
The whole arrangement of Professor Korn's
selenium instruments has now been described, and
there remains only the description of the actual
commercial working to be given. It is clear
that there must be some means of communication
between the operators of the sending and receiving
machines . As a metallic circuit is necessary owing
to the weakness of the current transmitted, tele-
phone lines are employed, and these must be quite
isolated and free from annunciators or shunts. A
convenient arrangement is made by which the
operator can switch at will the line into his instru-
ment or into the telephone. The switchboard is
shown in Fig. 21 .
There are two change-over telephone switches
on the board as shown. The change-over contacts
of one are connected to two terminals AA, which
lead to the receiving machine, denoted by G for
convenience. One of these lines passes first through
the milliampere metre MA to indicate the strength
of the line current. The change-over contacts of
the other switch go to the telephone line. It will
be seen that when the switches are in the position
shown the telephone line goes direct to the tele-
phone T, and the machine terminals are in connec-
tion with a 1,000 <Q resistance R. When switched
over towards the right the machine is in connection
with the telephone line, and the telephone instru-
ment is out of circuit. The three terminals C give
46 PHOTO-TELEGRAPHY
100 and 200 volts to the selenium cells in the
manner already shown in the compensation
diagram, while current is led from P to the motor
and galvanometer magnets.
It is hardly necessary to say that accumulators
'mm
FIG. 22. Prof. Korn at the telephone, when awaiting
the first picture from Paris in 1907.
are essential in order to ensure smooth running and
constant current.
Much trouble is experienced with some selenium
cells, while others will last without any bother for
many months. The " fatigue " often spoken of is
really a permanent lag in the cells; a definite
physical change appears gradually to take place in
FAULTS OF SELENIUM
47
the selenium with the result that they are less
sensitive to light, and the ratio of their " light
sensitiveness " to " dark sensitiveness " becomes
less. They are sometimes enclosed in glass cells
which are sealed and exhausted, but this is not
done in the case of Professor Korn's machines. A
cell is liable sometimes to get into a certain state
which renders the current " intermittent/' i.e.,
continuous but always
variable, the variation
amounting perhaps to
10 or 20 per cent. This
trouble would appear to
be due to bad contact
somewhere, but it is in
reality a fault of certain
old cells. The most
successful working of
the selenium machines
was obtained after
adopting the method patented in 1908 by Professor
Korn for keeping the cell always slightly illuminated,
so that the inertia was overcome. If the curve given
in Fig. 23 represent the effect of light of increasing
intensity upon the current (or reciprocal resistance
of the cell), then that portion of the curve shown
would be the best to use for photo-telegraphy, where
r*
the ratio - is more or less constant ; {hat part of the
/n this portion
1 1 1 u m ina tio n
FIG. 23.
48 PHOTO-TELEGRAPHY
curve to the left of the first vertical line represents the
amount of light continually falling on the cell before
any additional illumination from the photographic
transparency falls upon it. Within the portion
2\c*
selected -^- is almost constant, and on it will depend
largely the shape of the triangular aperture in the
receiving diaphragm.
The first photograph wired by Korn's new sele-
nium machines was received from Berlin at the
office of the French illustrated weekly paper,
L? Illustration, in October, 1907. It was a photo-
graph of President Fallieres, and came through
with considerable success. The first night of the
trials Berlin-Paris, Professor Korn and his wife,
his assistant Herr Will, and several post office
officials, and some of the leading newspaper men
of Paris, were present. As the telephone lines were
to be required for an hour or two, it was necessary
to make the experiments very late, and the line was
promised for midnight. After some minutes we
got the connection with Berlin, but there was an
annunciator bridged across it, and we could get
practically no current at Paris. Every effort was
made by the Director of Telephones, and we all
waited patiently until after two o'clock in the morn-
ing, with no result, and finally everyone was obliged
to leave, feeling both tired and disappointed.
On the next occasion, however, the picture of
FIRST TRANSMISSIONS
49
Fallieres was received, and a photograph wired to
Berlin from Paris. At Berlin Dr. Glatzel was
in charge, the instrument being installed at the
office of the Lokal Anzeiger.
A few days later Professor Korn left for London,
leaving M. Chatenet at
Paris as operator, and
I brought the Daily
Mirror instrument
with me to London.
The Paris and London
instruments had been
made by J. Carpentier,
the well-known scien-
tific instrument maker
of the Maison Rhum-
korff.
The Paris-London
photo-telegraphic ser-
vice was inaugurated
on November 7th,
1907, when Professor
Korn received the first
photograph from Paris at the Daily Mirror office.
Every facility was then and has since been given by the
officials of the General Post Office, and much courtesy
has been shown throughout by Major O'Meara, Mr. F.
Tandy, and other of the chief telephone engineers
of this country. The two above officials were
FIG. 24. One of the first photo-
graphs wired by Korn's com-
pensated selenium machines.
50 PHOTO-TELEGRAPHY
present at the first Paris-London trial, and attended
the lecture given by Professor Korn on that
FIG. 25
occasion. The photograph first wired to London
was one of King Edward VII., and it is repro-
duced in Fig. 25. The original was an exceed-
LINES IN PHOTOGRAPHS 51
ingly good photograph, eminently suited to
the selenium process, and it is a peculiar
fact that, as far as an actual face is con-
cerned, that photograph still remains the most
perfect ever transmitted, putting aside the purely
technical peculiarity of the stripes or bands of which
it is composed. These lines in the photograph
correspond to the threads of the screw axle ion which
depends the upward travel of the receiving drums,
and they make an angle with a line drawn hori-
zontally across the greatest length of the picture of
approximately sin~ J (-p-l. The lines can be got
rid of by placing the small lens which concentrates
the light from the triangular diaphragm upon the
film at a greater distance from the film, but the
sharpness of definition of the photograph then at
once suffers. This may sometimes be all the better
in the case of a portrait where the diffusion renders
the result much more " photographic/' But the
sharpest definition is necessary where any attempt is
made to telegraph a picture with any small detail
in it. " Small detail " is in itself a limited term,
as only very bold and simple subjects can be trans-
mitted with apparatus of this size, and hence its
almost exclusive application to the telegraphy of
portraits. The lens above referred to should cast
an image of the triangular aperture on the film
which is almost a point.
E 2
52 PHOTO-TELEGRAPHY
More contrast could be got in the received pic-
tures by placing over the diaphragm a graduated
glass, made by exposing a photographic plate to a
fixed light some distance away and gradually
uncovering it, so that on development one end
is very dense, the other very transparent, density
graduating into transparency. By cementing such
a glass to the diaphragm so that at the apex you
have a dense part gradually becoming more trans-
parent as you approach the base, the effect is to get
far more light through as the shutter uncovers the
triangular hole than would be the case otherwise.
About the time of the first trials with Korn's sele-
nium apparatus, the submarine telephone lines link-
ing this country with France were rather faulty,
and it was only occasionally that we were able to
have line for experimental purposes. The average
business telephone call lasts six minutes, and in
these early days we wanted it for at least half an
hour ; hence, when one or more lines were " down,"
the pressure on the others was so great that the
telephone authorities were quite unable to give us
the use of one. The consequence was that experi-
ments were few and far between, and often we found
the line quite good for the purposes of ordinary
telephony unsuitable for our own trials. This
state of affairs continued for some months, but in
the spring matters improved, and we were able to
make numerous experiments, generally obtaining
EARLY EXPERIMENTS
53
FIG. 26.
the line for about half -an -hour soon after eight
o'clock. The results were affected by various
factors, the chief of them being leakance. Three-
quarters of a milliampere is about the minimum
54 PHOTO-TELEGRAPHY
current possible to work with, and we frequently
only received about half. The optical arrange-
ments could, of course, be easily modified to com-
pensate for this, but unless the tension in the
galvanometer strings was above a certain figure,
its action was uncertain.
Induction from other lines was very marked at
certain times, and at first it was thought that this
was due to weather conditions. The observed
facts, however, showed this not to be the case ;
induction effects were chiefly due to line condi-
tions. The two systems of telegraphy, Morse and
Baudot, gave marked induction effects, and tele-
graphic experts declared they could actually read
Morse messages on some of the photographs.
Induction effects can be seen on looking at the
photograph shown in Fig. 26, where they cross
the photograph at regular intervals.
The photographic image, as will have been
gathered, consists really of one long spiral line of
varying thickness and intensity, which becomes
resolved into parallel lines when the image is
changed from its cylindrical form and laid out flat.
The thickness of the line is increased by the in-
duction, hence the dots and dashes are graphically
represented in the received photograph.
In the Baudot telegraphic system there is a
periodic current, and the stripes seen are at
regular intervals across the picture. These marks
EARLY TROUBLES
55
were at first presumed to be due to some mechanical
trouble.
cd
CU
OH
ed
CD
d
ri
<-W
o
'E.
W
Photographs telegraphed from Paris now became
a fairly regular feature in the Daily Mirror y and a
56 PHOTO-TELEGRAPHY
great many people, among them some of our lead-
ing scientific men, began to watch the results with
curiosity. Some of them doubtless wondered
whether the system would ever have much com-
mercial utility, and the limit set to the process
owing to one being confined to the transmission of
portraits made this easily understood. It was not
until the installation of Korn's telautograph (see
next chapter) that the enormous possibilities of
photo-telegraphy became clear.
The Franco -British Exhibition took place in
1908, opening in May, and the selenium machines
were exhibited there by the Daily Mirror in a small
pavilion erected for the purpose. The drawback
to such a method of demonstration was that, beyond
watching the movement of the galvanometer shutter
and the revolving photographic transparency, little
was to be seen. A trunk line was installed, and
photographs were received from Paris at the pavi-
lion each evening that the line was available. A
picture of the King was transmitted at four o'clock
on the afternoon when His Majesty formally opened
the exhibition.
The great fire which occurred in September,
1908, and burnt the Paris telephone exchange to
the ground, will doubtless be remembered. This
effectually put a stop to photo -telegraphic experi-
ments, and little more was done except to give
demonstrations to the visitors. As a general rule
THE MANCHESTER STATION 57
the whirring noise of the motors excited the
curiosity of people outside the little pavilion, and
large crowds endeavoured to come inside, a queue
some fifty yards long occasionally awaiting their
turns outside. The pavilion would get so full that
those farthest away from the barrier could see
nothing. On one such occasion two elderly ladies
squeezed their way in, and after waiting patiently
some ten minutes and seeing nothing but the backs
of other people they came out again, and the
following conversation ensued :
FIRST LADY : " How very wonderful it is ! "
SECOND LADY: "Extraordinary! Marvellous!"
FIRST LADY : " Did you see anything ? "
SECOND LADY : " No, I could see nothing. Did you see
anything ? "
FIRST LADY : " Nothing."
The demonstrations continued until the close of
the exhibition, by which time they badly needed
overhauling. This took some time, and when
finished, it was decided to instal one of them at
Manchester, in order to facilitate the transmission
to London of north -country pictures.
The instrument was placed at the offices of the
Manchester Courier, the installation being as follows:
One 80 ampere hour no volt set of accumulators, with
charging board, etc., for the motor, lamp and magnet.
One 2 ampere hour 210 volt set of accumulators for the
selenium cell line circuit.
Trunk Telephone and change-over switches as described.
58 PHOTO-TELEGRAPHY
The line from Manchester was shorter and more
satisfactory for the selenium machine than the
Paris- London line, and the results obtained were
very fair. Photographs were frequently tele-
graphed to Manchester and published in the Man-
chester Courier, while every evening some portrait
of topical interest was sent from Manchester to
London. Soon after this service began, the Paris
lines were again available, and the Paris-London
service was again continued.
Several experiments were made with a view to
transmitting landscapes or sporting pictures instead
of simple portraits by dividing the original picture
into two or three parts and telegraphing one part at
a time, afterwards joining up the sections. This
method is quite plausible in theory, but unfortu-
nately only worked out in practice in the labora-
tory. Each portion takes twelve minutes to
transmit, and often during such time the condi-
tion of the lines would vary sufficiently to render
the next portion quite different in character.
These differences could have been made good
by retouching, had the time available permitted
of it. But it must be remembered that where
a photograph is telegraphed, it is usually sent
at a late hour, and if much time be spent on
the retouching, it may be too late for publica-
tion.
The public is very suspicious, and scientific men
JOURNALISTIC USES 59
are apt to ignore or disbelieve things with which
they are not personally intimate, and the opinion,
I know, prevailed at one time that many of the
telegraphed pictures were greatly retouched or
" faked " before they were printed in the paper.
Let me say here, therefore, once for all, that tele-
graphed pictures have, of necessity, less retouching
than the ordinary photographs, and unless they
arrive over the wire tolerably good in quality they
are absolutely useless. The idea that the results
were faked arose from mere ignorance of the vital
conditions under which commercial photo -tele-
graphy is possible.
The selenium machines were kept running at
Manchester and Paris until Professor Korn had
completed tests between Berlin and Paris with his
telautograph. They served a useful purpose, as
they inaugurated a new branch of electrical science
which is destined to play an important part in
modern illustrated journalism. An instance of the
criminalistic possibilities of photo-telegraphy was
shown in 1908, when a man named Hedemann,
whose photograph was telegraphed from Paris to
London and published in the Daily Mirror, was
recognised by someone in London who knew him
and gave important information to the police.
Professor Korn is at present endeavouring to
render more satisfactory his compensation of the
lag in the selenium cell, and eventually to prepare
60 PHOTO-TELEGRAPHY
instruments based on selenium for experiments
across the Atlantic. Herr Riihmer, whose work in
connection with wireless telephony is well known,
and who has contributed many valuable papers on
the physical properties of selenium,, claims now to
have completely overcome inertia in certain new
cells he has made. He is using selenium cells in
experimental trials to transmit by electricity a visual
image of an object or person, but as his work con-
cerns television and not the telegraphy of pictures,
it will not be discussed here.
CHAPTER III.
THE KORN TELAUTOGRAPH PRINCIPLES OF
WORKING ADVANTAGES OVER SELENIUM-
EARLY WORK WITH LINE PICTURES EXPE-
RIMENTS WITH TELEPHONE AND TELEGRAPH
CABLES RECENT PROGRESS WITH THE
TELAUTOGRAPH.
THE telautograph as arranged by Professor Korn
is really a combination of Caselli's transmitter with
the Einthoven galvanometer and photographic
receiver as used in the selenium machines. From
the very first the stringent limitation to simple por-
traits dictated by the use of the selenium instru-
ments was felt, and with the introduction of the
telautograph a new and commercial field of work
was opened up. There are doubtless a great
number of important or interesting men and
women in the world, but there are every day
hundreds of interesting " news snapshots/' and
while portraits of the former become more or less
exhausted at times, the " photo d j actualite " is
always obtainable and commands interest.
The first function of the telautograph was to
telegraph sketches or drawings in line, the sketches
62
PHOTO-TELEGRAPHY
being drawn with a pen and some ink that was
essentially an electric insulator upon a metal base.
Thus the first materials sent to me by Professor
Korn were some sheets of copper foil, a quill pen
and some ink composed of an alcoholic solution of
shellac strongly tinted with a violet aniline dye.
Now, if we draw a sketch on copper with this ink,
and connect the under side of it, i.e., the plain
FIG. 28.
copper side, with one pole of an electric battery B
(see Fig. 28), the other pole of which is connected
to one terminal of a galvanometer G, and we
connect the other galvanometer terminal with a
pen P, this consisting of, say, a darning needle,
and we now draw the " pen " slowly over the surface
of the sketch, we shall see that whenever the pen
crosses a line of the drawing, i.e., a shellac line,
the galvanometer needle is at zero, while when the
pen is in contact with the bare metal correspond-
ing to the paper of an ordinary sketch the galva-
nometer needle is deflected.
THE TELAUTOGRAPH
In this simple experiment you see the whole prin-
ciple of the telautograph, essentially different from
the system described in Chapter II. ; the galvano-
meter G represents the receiving apparatus, the
sketch on copper and the needle tracing over it
represent the transmitter. We shall now see how
this system works out in practice. A diagram-
BE
i
(NJIIIW. : 1
\w
FIG. 29.
matic representation of the transmitter is shown in
Fig. 29.
On a substantial iron base two uprights are
fixed, and the metal drum D fits on flanges on
a steel shaft which turns between centres ; this
cylinder is turned true in the lathe. Along the
top is a cylindrical steel bar FG, and over this
slides a substantial tube PQ to which is fitted
the carrier of the steel "pen" or stylus. An
arm fitted with a half -nut N projects from one end
of the tube, and the right-hand part of the steel
64 PHOTO-TELEGRAPHY
shaft is cut with a thread, about 20 threads per
centimetre ; W represents the cog wheel of the
motive arrangement, so that as the shaft turns the
nut N slides along and so imparts to the stylus S a
lateral motion, hence the stylus traces a spiral path
over the surface of the picture, which is fixed round
the revolving drum D.
The motive power is again a motor with two
slip rings fitted to the armature, so that alternating
current is generated for the actuation of a frequency
meter. The motor turns at 3,000 revolutions per
minute, and the speed is geared down so that the
cylinder revolves once in two seconds. As the
receiving apparatus is placed on the same table as
the transmitter, and contains as its essential part
the string or Einthoven galvanometer, it was found
necessary to mount the motor on a separate stand
and to connect it with flexible shafting. In the
most recent apparatus the motor and gear box are
mounted together on a stand fixed rigidly to the
wall, and flexible shafting connects the gear box
with the cog wheel that engages with the wheel W
shown in the diagram.
The dimensions of the cylinders used at London
and Manchester are 63*5 mm. diameter and
130 mm. length. In the apparatus first installed
by Professor Korn at Berlin and Paris he employed
a small cylinder the same size as the receiving
drum, but it is a considerable advantage to have
THE STYLUS 65
the transmitting cylinder double the size of that
used in the reception.
The stylus consists essentially of a finely -pointed
needle, and ordinary gramophone needles set in
a suitable holder have been used with success ; the
best form of stylus is one originally designed by
Mr. Sanger Shepherd, and its form is indicated in
the diagram. The stylus, made of steel or other
suitable material, is of the shape shown, and has a
small tube put through it about the middle, which
acts as an axis. Two needle-point
bearings fit into this finely-drilled
tube, so that it is free to turn with
minimum friction ; one end of the
stylus is bent downwards and is
pointed sharply, the other has a hole through it to
which is attached a tension spring, so that the
pressure of the style on the cylinder can be regulated.
The sparking at the point of contact is apt, if not
sufficiently well overcome, to quickly blunt the stylus,
and Mr. Shepherd prepared several with iridium
points let into the steel " head " ; these proved very
satisfactory, but were eventually replaced by a
modification which was designed to facilitate the trial
of needles of various materials, working at different
angles to the surface of the drum. This design is
shown in Fig. 30.
Here H is the head of the stylus, drilled so that a
needle AB can be fitted into it and clamped by the
P.T. F
66 PHOTO-TELEGRAPHY
screw S ; TT is the finely-drilled tube into the ends
of which the needle points fit. Steel needles, sharply
pointed, are at present in use in these holders, and
the tension is set such that the point does not scratch
soft lead foil when attached to the drum.
These remarks regarding the stylus apply to the
Daily Mirror machines, a somewhat different
arrangement being employed by Professor Korn.
The mechanism of the stylus is, however, a matter
of the greatest importance, as is also the shape of
its point and the angle that it makes with, the surface
of the drum.
The sparking at the point of contact of stylus
with copper foil sketch may be almost overcome
by shunting across it a condenser of about i to 1*5
microfarad capacity ; the extent of sparking is pro-
bably dependent to some extent on the self-induc-
tion of the line and may not therefore be always
equal. Sodium sulphate cells have been used by
Korn with great success also.
A battery of from 30 to 60 volts is usually
employed at the sending station, and the amount
of current received at London from Paris averages
between 6 and 1 2 milliamperes ; from Manchester
between 9 and 18 milliamperes.
The function of the transmitter is clearly to send
an electric current to the receiver, which is broken
constantly, the duration of the brakes depending on
the width of the shellac lines of which the sketch
THE TELAUTOGRAPH
67
is constituted. We shall now see how this inter-
mittent current is utilised to form a photographic
image in the receiving apparatus.
Fig. 3 1 gives a diagrammatic representation of
the sending and receiving stations . At the former
we have the drum D and stylus S and the battery B.
At the receiving station we have a drum DI half the
size of the transmitting drum, so that the received
Sending
Station
Receiving
Station
FIG. 31.
picture is one-quarter the size of the sketch trans-
mitted. This drum revolves in a light-tight box,
and is fitted with a steel shaft cut with a screw
thread 100 to the inch, or about four to the
millimetre. The shaft turns in a fixed nut, so that
a lateral motion is given to the revolving drum,
its motion thus corresponding precisely to, that .of
the transmitting cylinder. A sliding lens is fitted
in the centre of the front of the " dark box," and
in front of it is placed an ebonite screen, with an
adjustable slit fitted centrally and opposite the lens.
Any light passing through the slit is focussed by
the lens as a small spot of light on DI, and if the slit
K 9.
68 PHOTO-TELEGRAPHY
were always illuminated by a constant amount of
light, a sensitive photographic film wrapped round
the drum DI would receive a long, thin, spiral line of
exposure .
Now, however, imagine a line drawn from the
centre of the filament of the Nernst lamp N to the
slit, this line produced coinciding with the optic
axis of the small sliding lens in the dark box. A
condensing lens C projects the light from N upon
the ebonite screen in which the slit is fitted.
The light passes through holes bored in the pole-
pieces of a powerful electro -magnet M, across the
field of which is stretched a single flat silver wire
WW, and the shadow of this wire is thrown sharply
over the slit, the adjustment being carried out by
means of the sliding lens L. The magnet is excited
by 1 1 o volts i ampere from a battery of secondary
cells, and the current from the connecting telephone
line is passed through WW.
When current flows, this wire is laterally dis-
placed, and consequently its shadow rises above the
slit and allows the light from N to reach the
sensitive film on DI. Should the current received
be more than is required just to uncover the slit,
the necessary amount of extra resistance may be
inserted in series with the line.
A small battery opposing the line current may be
inserted at E as shown, and a regulating resistance
R shunted across the galvanometer. By means of
THE BACK CURRENT 69
the latter the movement of the wire WW can be
readily controlled, for if the line resistance be w\
and the resistance at R be w 2 , then the ratio of the
current entering the " string " WW to that
absorbed by the shunted resistance will be . In
w\
considering displacements of the string which are
very small compared with its length, we may regard
the displacement as proportional to the current.
Hence, by varying w%, w\ remaining constant, the
displacement can either be regulated to work with
a slit of any desired width or to accommodate a
current received of any strength, the width of slit
remaining constant.
In much of the work the battery E was put in
series with the resistance R, so that current flowed
continuously through the string and gave it a dis-
placement opposite in direction to that caused by
the line current. This procedure conduces to
" dead-beatness," and it brings the string back to
the zero position very rapidly the moment the line
current is interrupted. The ratio of the " reverse "
current to the " line " current is best varied to suit
the circumstances, but if the latter be fairly uniform,
the most desirable plan from the operator's point
of view is to keep E and R constant, and to adjust
the movement in the string caused by the line
current by means of a regulating resistance in series
with the line.
70 PHOTO-TELEGRAPHY
The currents transmitted by this system being
considerably greater than those practicable with the
selenium apparatus a somewhat different system of
synchronising the two instruments is required.
It becomes necessary, in fact, to reverse the direc-
tion of the current at the moment of synchronising.
The drum of the receiving apparatus is revolved
about i per cent, faster than the transmitting drum,
and finishes its revolution rather before the trans -
N
mitter, as in the case of the selenium machines.
When the turn is completed the drum is checked by
a metal stop, and the galvanometer circuit auto-
matically thrown out, a relay circuit being switched
in in its place. The transmitting drum on com-
pleting its turn causes a fleeting contact to be made
in the reverse direction to that of the line current,
and this actuates the relay, which, being polarised,
is only sensitive to current in the one direction.
The relay closes the local circuit which removes
the check by means of an electro -magnet, and both
CURRENT REVERSERS 71
drums therefore start off on a fresh revolution in
unison.
The reverser is of various forms, and is, of
course, used in most electrical instruments which
require similar synchronisation. One pattern of it
is seen in Fig. 32. Here, M, N are two steel
tongues with platinum contacts attached to a bar
which can rotate about a fulcrum 1 F ; it is held in
position by a spring S, the end of which is attached
,
> 1
j, -i
f \ \
FIG. 33.
to a point T, in this case in the bed -plate.
A represents a projecting pin on the cylinder or
drum, which, in the position shown, depresses the
end of the bar and consequently causes the tongues
M, N to rise. As soon as the drum has travelled a
little further round, the pin A is out of the way,
hence the spring S pulls the tongues M, N down
again into their normal position.
The next diagram (Fig. 33) represents the revers-
ing arrangement. M, N are again the tongues,
while P, Q and R, S are four platinum contact pins.
72 PHOTO-TELEGRAPHY
In the normal position of the springs they press
against the pins R, S, which are connected in the
manner shown to the terminals of the " line."
When the synchronising pin comes into contact
with the bar the tongues are raised into close
contact with the pins P, Q, so that clearly the
polarity at the line terminals is reversed. P, Q are
the receiving circuit relay pins of the transmitter,
while R, S are for the galvanometer circuit.
Towards the end of the year 1908 Professor Korn
installed one of his telautographs at the offices of
L' Illustration in Paris, another being at the Lokal
Anzeiger offices in Berlin, under the supervision of
his colleague, Dr. Glatzel, and a sketch was trans-
mitted with considerable success, the subject being
that of an aeroplane flight. The subject was
topical, and the picture was published the following
morning in Le Matin, with an article, descriptive
of the event, entitled " Prodigious." And considering
the fact that a complicated news picture had been
wired some 800 miles in ten minutes, that would
have taken several hours to come by train, for
the first time in history, the enthusiasm of the
Matin was certainly justified. I arrived in Paris
the. following morning and saw large crowds
of people looking at the photographic print,
which was displayed in the way customary with
the Matin in their windows facing the Boule-
varde. A few days later a telautograph was being
TELAUTOGRAPH EXPERIMENTS 73
constructed by Mr. Sanger Shepherd for the Daily
Mirror, and every effort was made to finish it in
time for the King's visit in January, 1 909, to Berlin.
Pictures were wired from Berlin to Paris of His
Majesty driving through the streets of Berlin, and
from those further pictures were prepared by M.
Chatenet, which he attempted to re -transmit from
Paris to London. But the London telautograph
had only been tested a day or two previously, and
was not in anything approaching good adjustment,
and the results were not good enough for publica-
tion. This was after attempting the transmissions
from about i A.M. to 3 A.M. Results soon began
to come through with regularity, however, and the
telautograph became a useful means of obtaining
news pictures from the Continent.
An interesting break in the telautograph trans-
missions was caused by the great Postal strike in
France, which was at its worst during the summer
of 1909. The pressure on the telephone lines was
very great at this time, as so much correspondence
was carried on by means of the telephone, and it was
only occasionally that the Post Office was able to
spare a line for the photo -telegraphic work. On
one occasion a picture was being transmitted, and
the adjustments had taken a minute or two longer
than usual ; the line could only be spared for about
fifteen minutes, and when this time had elapsed the
officials were obliged to cut our line. The picture
74 PHOTO-TELEGRAPHY
was only about two -thirds transmitted, and the
result was that the photograph was only received in
part ; needless to say, the more important part of
the subject was missing, and the result was quite
useless for publication.
Experiments were carried out between Berlin and
Paris, using one line only and an earth " return " ;
the current received in this way was about 5 milli-
amperes, and sufficient to work the apparatus satis-
factorily.
A second English telautograph was begun in
February, and an effort was made to have it ready
and installed at Manchester in time to telegraph
down to London the finish of the Grand National
race at Aintree in March. A change was made at
the same time in Manchester, the photo -telegraphic
installation being removed from the office of the
Manchester Courier to a new office specially
equipped for the work. A few days before the race
took place the new telautograph was taken to Man-
chester, and through the courtesy of the Post Office
officials there a trunk line was put in and tested just
in time to enable one experimental picture to be
wired through. The finish of the race was taken
by a press photographer, and the plate taken by a
Daily Mirror motor car to the station at Aintree,
and brought thence by train to Manchester. It
was then developed and a fish-glue print of the
picture was prepared and at once wired to London.
ADVANTAGES OF TELAUTOGRAPH 75
Such instances as this show how by means of
photo -telegraphy a newspaper can publish a picture
of some event a clear day before another paper. A
few critics are still sceptical, and say : " Would
not the public prefer to wait the extra day and have
FIG. 34. Reception to Sven Hedin, wired from Paris
to London by Telautograph.
a better picture the original? ' The answer is :
" No." Just as the public prefer to have a brief
telegram about an important event rather than wait
another day for the full report, so they prefer
to have a graphic representation, i.e., a photo-
graph, immediately. The advantage to the Daily
Mirror of having interesting pictures by wire before
76 PHOTO-TELEGRAPHY
any other paper is, in fact, obvious. During the
great trial of Madame Steinheil photographs that
had been taken in court late in the afternoon were
telegraphed to London soon after 7 o'clock. The
time of preparation of the photographs is, of course,
a factor of importance ; in the earlier days it was
customary for an artist to draw a line sketch of the
photograph to be telegraphed, and this sketch was
then copied in the camera, and a fish-glue print
made from the negative on copper foil. But
various improvements in the apparatus have gradu-
ally rendered possible the transmission of half-tone
photographs, and thus the work of the artist is
done away with, together with his time.
The preparation of these half-tone photographs
will be more fully considered in the chapter dealing
with the telectrograph, but mention may here be
made of the work done by M. Chatenet, which has
helped considerably in determining the best means
of producing them.
The progress in transmission has been due, as
stated above, to continual small improvements in
the apparatus. The galvanometer is the most
delicate, as well as the most vital, part of the instru-
ment, and it is the greater perfection of the moving
part of the galvanometer that has contributed to
the improved nature of the results.
A very small period is necessary in the " string/'
and its weight must be very small and its strength
THE GALVANOMETER
77
comparatively great. A flat silver string appears
to be more rapid than any form of phosphor-
FIG. 35. Example ot Fashion Plate wired by the
Korn Telautograph.
bronze, and the length of it free to swing is usually
about 5 cm. An improvement introduced recently
78 PHOTO-TELEGRAPHY
by Professor Korn is to have a flat string slightly
twisted, and the most recent galvanometers have
been provided with a collar, which can be turned
through a small angle, and this has a micrometer
scale to it, so that the angle through which the
ribbon is twisted can be accurately determined.
By using a wide slit in front of the receiving
box so that more light is admitted to the receiving
drum, with a consequent larger movement of the
shadow of the ribbon or string, it is possible to
receive the picture direct on photographic paper.
This is important, as it saves one operation in the
photographic work, and a minute or two fre-
quently decides whether a picture can be " got
in " an early edition of the paper or not.
The inertia of the photographic sensitive film
plays an interesting part in the more brilliant
results obtained direct on sensitive paper. When
the wider slit is used the tension of the galvano-
meter string is made less so that the shadow
will rise to the necessary extent to quite open
the slit. As it rises and falls each time there
is a current sent through the string, the light
is obviously greatest at the moment when the
slit is totally uncovered and is least at the two
instants when the slit is just a little opened and
nearly closed. Now before light can produce a
developable effect in a photographic film it has to
overcome the chemical inertia of the film, and unless
DUPLEX TRANSMISSIONS
79
it be of sufficient intensity to do this, nothing is
obtained on development. The result is that if the
complete upward and backward displacement of
the string takes a time T, and during that time
the sensitive film on the revolving drum is travel-
ling with a velocity v, the length of the mark
produced on development will not be rT, but
will be vt, where t <; T and the distance v (Tt)
To Earth
To Earth
To Earth
To Earth
FIG. 36.
corresponds to the inertia of the film. Con-
sequently the darkest parts only of the component
dots of the picture are given in the developed print,
and there is more contrast in the picture.
Simultaneous transmissions in two directions
have been recently suggested by Professor Korn,
which would reduce the cost of photo -telegraphy,
and save operators' time as well. The scheme is
seen at a glance in Fig. 36. The parallel lines
represent the telephone lines between the two
stations. AI is the transmitting flrum of one
machine, GI the string galvanometer; A 2 and G 2
8o PHOTO-TELEGRAPHY
are the similar parts of the other instrument. One
wire of the telephone line is used in each case for
the return, the current flowing through the earth.
This method has not so far been practically tested,
but will doubtless be useful when a greater number
of photographs are transmitted.
The question of the greatest possible length of
transmission by the telautograph is daily becoming
more important. In 1 908 an experiment was made
with Korn's selenium machines between Berlin and
London, the two lines Berlin -Paris and Paris -
London being joined at Paris by M. Chatenet, who
acted as " intermediary." This was necessary
owing to the impossibility of speaking clearly from
Berlin to London ; anything spoken had therefore
to be said to the Paris operator, who " passed it on "
to the Berlin operator, and vice versa. Then,
when the adjustments were made, the Paris
operator simply connected up the Berlin -Paris and
Paris -London lines on his switchboard.
These experiments were, as already stated,
carried out with the selenium apparatus, and the
current received at London, about 0*25 milliampere,
was insufficient to work with. The stronger cur-
rent for the synchronising was sufficient to work
the relay, however, and as it is of the same mag-
nitude as the galvanometer current used in the
telautograph there is little doubt but that the latter
instrument could be worked effectually between
LENGTH OF TRANSMISSION
81
Berlin and London, and probably over distances
up to 1,500 miles.
O.
<D
d
Beyond this stage it would be necessary to have a
more sensitive relay for the synchronising, and a
more sensitive galvanometer. The latter is as easy
P.T. G
82 PHOTO-TELEGRAPHY
of accomplishment as the former. The silver string
in the galvanometer can be made finer ; I have
obtained them in this country less than 2^00^ i ncri i n
diameter., while by using the silvered quartz threads
suggested by Duddell for the Einthoven galvano-
meter a thread j^Joo^h i ncn diameter can be
employed. The magnetic field can also be greatly
increased by building the magnets considerably
larger and making the windings take enough
current for complete saturation of the iron. The
instrument then becomes exceedingly sensitive,
and it merely remains for the optical parts to be
suitably constructed.
As explained elsewhere, the string of the galva-
nometer should have a period which is neither equal
to nor a multiple nor sub -multiple of the period of
the interruptions due to the transmitting apparatus ;
this applies only to the transmission of half-
tone line photographs, which consist of a definite
number of lines per unit of length. The natural
period of the string can be varied in several ways.
It can most readily be measured by means of the
recording apparatus described in Chapter V. If
a short current be sent through the string by means
of suddenly tapping a Morse key, a jerk is given to
it and it is displaced through a distance d (at the
centre). It then swings back to zero and then past
the zero point, to a point distant d x from it
where d x is less than d. One has, in fact, a
PERIOD OF STRING 83
damped oscillation, and the string does not actually
come to rest for a definite time. During this time t
m
FIG. 38. Example of line sketch from photograph, wired
by the Korn Telautograph from Paris to London.
there may be n complete vibrations, from which the
natural period tjn can be ascertained. If the string
be made to cast a shadow over an illuminated
slit through which the light passes when it is
G 2
84 PHOTO-TELEGRAPHY
displaced, and this light fall on a rapidly travelling
band of photographic film, and a tap be then given
with the Morse key as above described, a record of
the' movements of the string is obtained. If the
rate at which the film travels be known, it is easy to
calculate the period of the galvanometer.
The string has a shorter period if its length be
shortened or its tension increased, and the damping
of its oscillations can be effectually increased if a
twist be given to one end of it in the manner
already indicated. The effect of damping can be
seen if we consider the equation of the move-
ment of the string, which is of the form
d = ae~ kt cos (nt -f- a )>
where d is the displacement ; ae ~ kt decreases as
t increases ; k is the damping constant, and e~ kt the
damping factor. K has got to be as large as pos-
sible, and can be made large if we increase the
friction at the ends of the string. Suppose the
string to be displaced still through the distance d,
where / is the elastic force, the work done is df ;
this is the measure of the potential energy of the
centre of the string, provided we subtract /, the
loss of energy through heating owing to the
friction ; I increases as / is increased, while d
is diminished for the same amount of current sent
through the string.
The rapiditv of damping is readily seen from the
diagram shown in Fig. 39, which is drawn to scale
PERIOD OF STRING 85
from an actual photographic record of a short
current sent through the galvanometer.
Returning now to the question of possible dis-
tance of transmission, it is clear that for a very
sensitive galvanometer the displacement for the
same current would require to be much greater ;
the period would be lengthened, / and / dimin-
ished, and the rate of working diminished also ;
with a silvered quartz fibre, the period would be
much longer than that of the flat silver ribbon now
FIG. 39. Damping of oscillograph string. The ordinates
represent the displacement, d.
in use, and the transmission would therefore be of
an altogether slower nature. The capacity of a
long line would be correspondingly higher, and
this would again necessitate slowness in the trans-
mission.
The theoretical limits of distance of transmission
are fairly wide, but the practical limits are unfortu-
nately very different. Yet such distances as those
between London and Rome, London and Marseilles,
etc., should be by no means insuperable.
That the telautograph could be put to other uses
than that of transmitting photographs is seen
from its ability to transmit writing. Written
86 PHOTO-TELEGRAPHY
matter comes out very clearly in the received pic-
FIG. 40. Example of half-tone photograph transmitted
from Berlin to Paris by Telautograph.
tures, as do maps and diagrams of all kinds. In
the case of typewritten matter, for which a blue
TELEGRAPHING WRITING 87
or violet ink is usually employed, it is necessary to
make a photographic negative, using an ortho-
chromatic plate and a yellow contrast filter in
front of the camera lens. The writing then
appears colourless in the negative, and hence dense
" black " in the fish-glue print made from it. Type-
written matter has been telegraphed successfully
from Paris to London.
It will thus be seen that a signature for banking
purposes could be sent by wire, the signature being
written direct in the shellac ink upon a clean sheet
of copper or lead foil. This, by the way, must be
scrupulously clean, and for the copper a weak solu-
tion of potassium cyanide may be used with advan-
tage. Another method is to rub the metal with a
cloth and some finely -powdered pumice-stone. The
telegraphy of signatures for identification purposes
may be an important feature of later work.
The telautograph may be said to have solved the
problem of commercial photo -telegraphy, and to
have directly stimulated the efforts of others who
may have contributed to the development of the
work, or who may be now endeavouring to con-
tribute to it in the future.
CHAPTER IV.
THE THORNE - BAKER SYSTEM DIFFERENCES
BETWEEN THE TELECTROGRAPH AND EAR-
LIER CHEMICAL SYSTEMS ^ELECTROLYTIC
RECORDS OF CURRENTS TRANSMITTED
THROUGH LONG CABLES THE THORNE-
BAKER LINE-BALANCEWORK WITH THE
ELECTROLYTIC TELECTROGRAPH.
THE simplest and most practical apparatus for
photo -telegraphy at the present time is fairly
admitted to be the telectrograph, which came
into use by the Daily Mirror in July, 1909.
It was seen in the first chapter that Bakewell
had obtained some promising results with his
chemical telautograph, in which he used a picture
produced in lines on a metal foil, the lines being
of an insulating character such as offered by shellac,
gum, or glue, etc.
One of his chief difficulties was found in the
synchronism, yet results were obtained, and some
of the most interesting of these were telegraphed
written matter. The telectrograph, by which
THE TELECTROGRAPH 89
name I have designated my own modification
of Bakewell's apparatus, has proved successful,
because (i.) all the mechanical parts have been
most carefully modelled on lines dictated by
innumerable failures and experiments, and (ii.) by
means of the line -balancer I have made the
receiving instrument of such a character that the
distortion, lag and line -surges met with when
working with long-distance cables can be instantly
overcome by simple regulation.
Mr. Sanger Shepherd, whose workmanship is
perhaps the most accurate and effectual of any
instrument maker in the world, undertook from
the start the constructional work, and to him
largely belongs the credit of the success of the
Daily Mirror's photo -telegraphic work. In trans-
mitting a photograph seven inches by five, made
up of fifty lines to the inch, the Caselli
stylus has to traverse 7 X 50 or 350 lines per
revolution. With one revolution of the transmit-
ting drum in two seconds we have 175 dots
per second recorded on the receiving paper. If
one dot were j^th of a second later than it should
be it would fall into line with the dot of the next
line in the line photograph. The figure of merit
in synchronisation requires to be within an error
of at least i in 500 to obtain intelligible results.
Thus the synchronising mechanism lias to be very
fairly " perfect," and it has been necessary to
go PHOTO-TELEGRAPHY
make the balancing of the stylus and various other
mechanical details equally precise.
If we refer to Fig. I (Chapter I.) we see that
at the sending station we have a revolving metal
drum A, to which the lead foil half-tone photo-
graph is attached. This revolves while . a stylus
traces a spiral path over the picture in virtue of
its being given a lateral motion. The style is
fixed to an arm (Fig. 28, Chapter III.), which
has screwed to it a half-nut, threaded so as to
fit on the shaft F, which is also threaded. Hence
as the shaft turns, between steel centres, the
half-nut travels along it, and so draws the stylus
along too. In the telectrograph there are 75
threads to the inch, so that the style moves later-
ally with a velocity of j^oth inch per second.
The style is of special design, as shown diagram -
matically in Fig. 41, turning about pivots P and
being provided with a tension screw T. The point
of contact is a V-shaped iridium tracer I, which
withstands the constant sparking caused by the
makes and breaks of the current. The actual
point must be very fine, yet not fine enough to
scratch the lead ; the tension is regulated by the
screw T.
The battery, usually 100 volts, consists of
secondary cells, and hence a series of currents
are sent into the line exactly as in the case of
Korn's telautograph. At the receiving end we
THE TELECTROGRAPH
FIG. 41.
have a cylinder B, the same size as A, and revolv-
ing in synchronism, its movement being con-
trolled in the way already described and in
common use in certain
systems of ordinary tele-
graphy.
Round B is wrapped a
piece of specially prepared
paper, containing in its
composition certain chemi-
cal substances which de-
compose on the passage
through them of an
electric current. The un-
decomposed chemicals must be colourless, the
decomposition products must be coloured. Hence,
in theory, whenever a current is sent from the send-
ing instrument it passes through the paper, via the
stylus, and a black or coloured mark is made on
the paper, the length of the mark, /, measured along
the circumference, being equal to tu, where u =
the velocity of the surface of the drum, and / the
duration of the current. When, however, the send-
ing and receiving instruments are connected by a
long distance line, instead of an ordinary resistance,
we find that for a current of duration t, the length
of the chemical mark is considerably greater
than tu.
If we were to send one brief current from trans-
9.2 PHOTO-TELEGRAPHY
mitting to receiving station, say of ^oo^ n secon d
duration, and we were to place a piece of chemically
sensitive paper on the receiving drum, the latter
revolving in the ordinary way, we should get
a mark of this form ^^, showing that the line
takes an appeciable time tc
charge up, and when charged,
requires time again to fully
discharge. This can be repre-
sented by the curve shown in
Fig. 42. If we were to transmit
several brief currents of equal
Tim e .
period, and were then to stop
suddenly, we should get a
continuity of marking, not dying away for an appre-
ciable time.
These difficulties can be almost entirely over-
come by the line balance described by me in
November, 1909,* in which a current with shunt
capacity and an inductance to time the phase
where necessary is sent into the line to damp
down the secondary surges. The arrangement
is seen in Fig. 43. D is the receiving drum
and S a platinum stylus. The shunt circuit
consists of two similar parts, a secondary
cell being in each, BI and B 2 ; a variable induct-
ance in each (not shown) ; and a variable resistance
of 1,000 ohms, RI and R 2 . The ends of the resist-
* Journal of the Society of Arts, 2975, 30.
THE LINE BALANCER
93
ances are joined in the manner shown, while
between the sliding contacts of the resistances is a
variable capacity K ; the capacity ranges from o
to i microfarad.
When a photograph is received the waves sent
into the line are distorted by their passage through
it, and this distortion appears as an elongation of
Tel e ph on e
Lin e
FIG. 43.
the chemical dots or marks made upon the paper
on the receiving drum as already described ; the
greater the distortion the less is the resistance
required in RI and R 2 ; the greater the capacity of
the line connecting the two machines tKe more the
capacity one must introduce by means of K.
It can now readily be seen how practical the
telectrograph is for commercial work. The
operator carefully watches the paper on the drum
during the first two or three revolutions, and
according as the marks are crisp, or blurred he
varies the various regulating elements. Hence
94 PHOTO-TELEGRAPHY
before any important portion of the photograph
has been transmitted he can ensure its reception
being good. In any optical method of reception,
on the other hand, should any error have occurred
in the preliminary adjustments, the operator cannot
know of his fault until after both the reception has
FIG. 44. i. Capacity on line. 2. No capacity. 3. Capacity
on line, but balancer in shunt.
Photograph showing the balancing effect of the Telectrograph
arrangement. Currents were sent to the receiver by
closing a circuit with a Morse key. The chemical marks
produced are elongated or "tailed" when capacity is
shunted on the line (i). They are short and end abruptly
with no capacity (2). The capacity effect is obviated by
the balancer (3).
been completed and the film or sensitive paper has
been developed. When we remember that the cost
of the telephone line between London and Paris is
four shillings for three minutes, or over a farthing
a second, the need for rapidity becomes apparent.
The machine must be simple, rapid, and, if pos-
sible, certain ; the preliminary tests and adjust-
ments reduced to the minimum, and the operator
himself must be quick and intelligent, and be able
to locate a fault rapidly.
CAPACITY EFFECTS 95
It is interesting to note that the distortion
caused in transmission through a long line or cable
is considerably lessened where there is high
leakance. Heaviside has shown that in telephony
the distortion D is given by the equation
R S
= T TK'
and the attenuation A by
R S
A-
-
where R is resistance, L inductance, K capacity,
and S leakance. When leakance is very small on
a line of considerable weight we have the dis-
p
tortion approximately proportional to -^=-.
2 \-4
The capacity effects are thus less pronounced
when there is much leakance on a line, if the latter
take place at various well distributed intervals, as
its effect is to obstruct the charging up of the line.
Capacity does not reduce the energy transmitted
along the line, but its effect, as well known in tele-
phony, is to cause length of time in discharge ;
the inductance is valuable as it counteracts the
distortion, but it is small in submarine and under-
ground cables, because the current flows through
the two lines, which- are close together, in opposite
directions, the self-i'nduction of each being thereby
largely neutralised by the other.
96 PHOTO-TELEGRAPHY
It is interesting to note that often during very
wet weather less " balancing " of the line is re-
quired in working with the telectrograph, this bear-
ing out the distortion expression
R S
2 L 2 K*
The capacity of a single line of diameter d and
length / at a height H above the ground is given
by the following expression :
r __ I X 2*415 X io 6
~ -- ~~~'
but this becomes effectively much less where there
are two lines close together. In the case of tele-
phone cables we can divide the capacity of one line by
two to get the total capacity of the closed line, since the
capacity of two condensers in series is equal to half that
of one singly. As will be seen later, the capacity of
a Paris London single line is 10*6 m.f., so that the
capacity of the two lines forming a closed circuit is
5 '3 m.f. The submarine cable between Sangatte
(France) and St. Margaret's Bay is 5*52 m.f. in
capacity, or more than equal to the total capacity of
the land lines, which measure 287 miles against 23
miles of the submarine,
The preparation of the chemical paper for
receiving the photographs is not an easy matter,
ELECTROLYTIC RECEIVER 97
as one must have a paper always conductive,
and therefore always in a moist condition, and
whilst it is sufficiently absorbent it must have
a smooth surface, as otherwise the grain is painfully
prominent when the picture is copied for reproduc-
tion. The resistance of the paper may be any-
thing from 1,000 to 5,000 ohms, and as it
must mark instantaneously with a current of about
i milliampere it requires to be extremely sensi-
tive. The speed at which the paper passes under
the stylus is 3*75 inches per second, and since
the amount of the element liberated which causes
the discoloration is by weight equal to the product
of current, time, and electro -chemical equivalent,
it is seen that an exceedingly small amount
of chemical action takes place. When much current
is lost in the line it is sometimes necessary to in-
crease the voltage at the sending end. Although
only about a milliampere of current flows actually
through the paper, twenty or thirty may flow
through the line, this excess of course going into
the shunt circuit or balancer of the receiver. The
secondary discharge of a small induction coil is
quite sufficient to mark the paper used, so that the
effect of electrolysis can be produced with prac-
tically " no current," provided the tension be
sufficiently high.
The first experiments were made with the telec-
trograph in 1909 at the Imperial International
P.T. H
9 8
PHOTO-TELEGRAPHY
Exhibition, Shepherd's Bush, where demonstra-
tions were given about eight times daily, photo-
graphs being telegraphed from one machine to the
other through an artificial " line " of about 2,000
FIG. 45. Portrait of first lady councillor
of Liverpool. Wired by the Telectro-
graph from Manchester to London.
12 resistance; the machines stood some 16 or 20
feet apart, so that both sending and receiving
operations could be readily observed together.
The method of synchronising was practically the
same as that described for the telautograph, except
MANCHESTER EXPERIMENTS 99
in so far as the receiving machine was concerned.
The " line " terminals were connected to the spring
tongues of the reverser (see Chapter III.), which
was in contact with two upper platinum pins
during nearly the whole revolution, these pins lead-
ing one to the stylus and the other to the drum,
i.e., the back of the sensitive paper. At synchro-
nism the check which stopped the drum revolving
temporarily automatically lowered the tongues into
contact with two other pins which led directly to
the polarised relay, the latter switching in the
mechanism for withdrawing the check.
The machines worked so satisfactorily over the
artificial line that in July, 1909, I was tempted to
place a similar instrument in Manchester, where an
installation of Professor Korn's apparatus was in
full swing, as already described. The first expe-
riments over this line, some 200 miles in length,
were very disappointing. The attempts were made
with line sketches, not half-tone photographs, and
the lines appeared on the paper as so many
smudges ; each mark had a long tail, and it was
evident that secondary discharges were coming
from the line into the paper. These discharges
were much more noticeable some days than others .
It thus became obvious that the capacity and
induction effects would have to be counterbalanced,
and after a series of experiments the means already
described were adopted, with what success has been
H 2
IOO
PHOTO-TELEGRAPHY
seen from the quality of the pictures telegraphed
with this instrument since published in the Daily
Mirror .
It has already been explained that a graduation
of tone in a photograph is
represented in a line half-
tone photograph by lines
becoming gradually nar-
rower. This tapering down
of the width of the lines in
the telegraphed picture re-
ceived is wonderfully repro-
duced, and the results are
therefore truly "photo-
graphic " ; indeed, examined
a short distance away, they
are, if the synchronisation
has been good, hardly distin-
guishable from the original
photographs.
In October, 1909, a telec-
trograph was installed in
Paris, but here again trouble
was at first experienced. In the first place, the line is
half as long again as the London-Manchester line, and
in the second, its various elements are distinctly dif-
ferent. The first picture received was successful, but
then the line conditions must have changed, because
for several days the results were extremely bad, each
FIG. 46. Portrait of Mr.
Howarth, telegraphed
from Manchester to
London by the Thome-
Baker Telectrograph.
o
a.
ed
LINE PHOTOGRAPHS 101
dot running into next, so that the whole surface
of the paper was discoloured and all the details of
the image hopelessly intermingled. I then in-
creased the capacity of the condenser in the line
balancer, and the photographs were also tempo-
rarily made with a coarse line screen (30 to the
inch), and the quality was at once better. A great
deal depends, needless to say, on the quality of the
half-tone photographs, which require quite a par-
ticular method. of preparation.
The method of making these photographs is as
follows : The picture to be telegraphed is pinned
flat to a board or placed in a frame with glass
over it, and fixed vertically in a copying apparatus.
It is usually illuminated with an arc lamp at
either side with reflectors. The camera used for
copying it has a half -tone screen fixed at a certain
distance in front of the sensitive plate. This
screen consists of a glass plate ruled with a certain
number of lines to the inch ; thirty or thirty-five
lines to the inch is known as a " coarse " screen,
the number for high-class illustrations, printed on
surfaced paper, being 120 upwards to the inch.
Usually two such screens are used, crossed so that
the rulings are at an angle of 90 to each other, and
then the picture is broken up into dots ; but it can
easily be seen that where the picture is put on a
cylinder and travels round beneath a tracing point,
lines are preferable to dots ; the lines of course lie
102
PHOTO-TELEGRAPHY
along the length of the cylinder, so that the tracer
scrapes over them and not along them. In the case
of dots the tracer would go in between two adjacent
ones very often, or, as its path is at a slight angle
FIG. 47. Half -tone single line negative image,
as ordinarily used for the Telectrograph.
to the path of a fixed point on the circumference
of the cylinder, it would occasionally touch two
dots in consecutive lines at once, and interfer-
ence would be caused.
The single -line screen has the effect of breaking
LINE PHOTOGRAPHS 103
up the picture into parallel lines which vary in width
according to the density of the photograph at each
point. Thus, in the case of a portrait, the dark
coat would be represented by wide lines close
together, a light part of the face by fine lines
correspondingly wide apart, the distance between
the centre of any two lines being always constant.
If there are fifty lines per inch, no line can be wider
than 5\j inch ; as a matter of fact, it should not
be wider than -^ t, where t is the width of the point
of the stylus, otherwise a dark' part of the picture
would appear in the telegraph as a " dead black."
The print from the half-tone negative is now pre-
pared by printing from it (in arc light) upon a
sheet of thick lead foil coated with a thin layer of
fish-glue rendered sensitive to light by means of
a soluble bichromate. When printed it is held
under a tap, and all the unexposed parts dissolve
away, i.e., the parts in between the lines. The
print is now dried and placed between two polished
steel plates, and put into a press. This causes the
glue image to sink into the soft metal without dis-
torting it, and a smooth commutator surface is
obtained, which therefore offers no resistance to
the stylus, while it allows of very intimate con-
tact between the stylus and the picture.
The image is made negative for the telec-
trograph, as wherever there is bare metal a black
mark is produced at the receiving instrument. The
104
PHOTO-TELEGRAPHY
image is made visible by staining up the print in
an aniline dye solution, the glue taking up the
colour readily.
Photo -engravers know that in making a half-
tone photograph, even with the cross screen, a good
deal of the detail is lost, and this is only natural
when we consider that, instead of a solid black or
grey, we have only dots on a white ground. In
FIG. 48. Finish of the St. Leger, wired by the Telectrograph.
making a single -line picture a great deal more is
lost, and thus before making the screen negative
the original has to be considerably retouched, the
contours have to be very clearly defined and accen-
tuated, and the paler tints have to be made con-
siderably bolder, as these lose the most in the
reproduction. The solid blacks, on the other hand,
require to be made grey, so that the lines repre-
senting them in the half -tone picture are not too
wide and close together.
LINE CAPACITY 105
Future progress rests so much on greater perfec-
tion being obtained in the line pictures that I have
dwelt at some length on these points. The present
systems are good and practicable ; it is perfection
of detail that is required. M. Chatenet is a par-
ticularly clever photo -engraver, and has rendered
much assistance in finding the best means of the
preparation of the half-tone pictures. A consider-
able time elapsed at Manchester before the photo -
engravers there were able to make really suit-
able line prints ; but, having once found out the
" right way/' the work proceeds quite smoothly.
But what I would like to point out is that,
although telegraphed pictures are now to be seen
so regularly in the Daily Mirror that they occa-
sion no surprise, they have only become what
they are through the attention from start to finish
given to minute details.
By means of the apparatus described in
Chapter VI. it has become possible to make a great
variety of experiments, transmitting pictures over
an artificial telephone line in which resistance, self-
induction, leakance, and capacity can be varied
at will. By examining oscillographic records of
these transmissions, various arrangements for over-
coming line faults can be tested, and their practical
utility estimated. The problem, of photo -tele-
graphy over telephone lines is closely allied in many
respects to ordinary telephone work, only that the
io6
PHOTO-TELEGRAPHY
electrical impulses are of far longer duration, and
represent small parts of a picture instead of vocal
sounds.
As the function of the transmitting instru-
ment is merely that of an interrupter, it is
clear that the sending bat-
tery can be included in the
receiving station, hence a
portable apparatus is not
impossible. Portable instru-
ments are now, as a matter
of fact, being constructed,
in which the motive power is
derived from a particular form
of clockwork mechanism.
The portable machine is the
key to general commercial
utility, and its developments
will be watched with interest.
One drawback to the
telectrograph, viz., that a
negative image had to be
used on the transmitting
cylinder instead of a positive (the latter being more
easily and rapidly prepared), has recently been
overcome. A positive print having about fifty lines
to the inch is used, and at the receiver a current is
passed through the electrolytic paper which con-
tinuously discolours it. The currents transmitted
FIG. 49. M. Riolle, Public
Prosecutor in the Stein-
heil case ; wired from
Paris to London by the
Thome - Baker Telec-
trograph.
DOUBLE CURRENT SYSTEM
107
from the sending machine are of opposite direction
to this continuous current, arid neutralise it. Hence,
whenever the stylus of the transmitter sends a
current through the line it neutralises the con-
tinuous current, and so prevents the latter from
making an electrolytic dot. As soon as the trans-
mitter current has ceased, it is immediately wiped
FIG. 50. News photograph wired from Manchester to London
of a railway accident at Stalybridge.
out by the continuous current, which is of course
shunted on to the telephone line.
The use of a double current system in telegraphy
is well known, and greatly increases the possible
rate of working, as it hastens the ordinarily slow
discharge of the line. It thus becomes possible
to work with finer screens in preparing the photo-
graphs, and to obtain a correspondingly greater
amount of detail.
CHAPTER V.
CONSIDERATIONS OF THE TELEPHONE AND
TELEGRAPH LINES AND THEIR INFLUENCE
ON PHOTO-TELEGRAPHY.
As the two qualities, leakance and resistance, of
the lines connecting two photo -telegraphic instru-
ments have a final influence on the limits of long-
distance transmissions, and the capacity and in-
ductance factors have a large influence on the
quality of the pictures and the rate, etc., with which
they can be transmitted, some short discussion of
the matter becomes necessary.
The actual effect of capacity is, as has been
pointed out elsewhere, a lengthening of the dura-
tion of the current, but we shall now see how these
effects can be experimentally demonstrated. A
modified form of the Einthoven, or string galva-
nometer, was employed to record photographically
the effects of capacity on the currents transmitted
through a high -resistance line by the transmitter,
as used in the telautograph and telectrograph. The
arrangement is seen in Fig. 51. A band of
sensitive film MOQ travels over rollers in a light-
tight box, being actuated by a well - regulated
OSCILLOGRAPH RECORDER
109
clockwork motor ; one or two strings (silver wires
Tcfeoth inch thick) are free to move laterally between
the tunnelled poles of the electro -magnet,, and a
shutter is attached to them where the optic axis
meets them. N is a Nernst lamp, and L a lens.
The lens in the tube T throws a real image of the
shutter over the horizontal slit S. The terminals
A, B of the galvanometer strings are connected to
the metal drum and stylus of a photo -telegraphic
M O'
FIG. 51.
transmitter, across which capacity can be shunted,
or inductance, etc., can be placed in the circuit.
Every time the stylus of the transmitter comes in
contact with the metal, current flows through AB,
which is laterally displaced ; hence the shutter
uncovers the slit S more or less according to the
current strength. A series of images of the slit is
thus seen on the moving film MOQ on develop-
ment. The elongation and widening of the image
due to capacity can be seen clearly on comparing
the two records shown in Figs. 52 and 53.
no
PHOTO-TELEGRAPHY
a
oj
o
o
G
>*
'o
03
03
EFFECT OF MOMENTUM in
These oscillographic records show many things
of great interest . Firstly, that if the metallic space
between each of several consecutive glue lines in a
half-tone print be s, greater than that si between
each line in another print, the current passing
through the strings A, B is greater in the case of
the s lines than in that of the Si, although the line
resistance, battery power, etc., be the same in both
cases ; hence a definite time is required for the
current transmitted to reach a maximum value, the
possible value not being so nearly reached when
the interruptions are very rapid as when slower, and
the maximum value being very rarely reached.
Secondly, that where a large number of consecutive
currents of equal period p are transmitted, the dis-
placement of the galvanometer strings increases
gradually to a maximum value, then decreases, and
so on, instead of remaining always equal and pro-
portional to p. Thirdly, -that when the period p
has a certain value, equa.] to the natural period of
swing of the strings, the displacement is excessive,
and very much higher than that obtainable under
any other circumstances, R and C remaining equal.
The effect of a pumber of currents of equal period
to cause a gradual extension of the swings which
reach a maximum and then decrease, indicates that
a dead-beat action like the electrolytic one is pre-
ferable to any form of moving part, where there
is definite momentum, and kinetic energy.
112
PHOTO-TELEGRAPHY
The overhead wires of the Paris -London tele-
phone line are 600 Ibs. copper wire in France and
400 Ibs. (per mile) in England. Their capacities
and resistances are as follows :
Capacity of
Length in
Resistance
each wire
miles.
in ohms.
in micro-
farads.
London to St. Margaret's Bay
84-5
183
1-32
St. Margaret's Bay to Sangatte
23'0
H3
5'52
(cable).
Sangatte to Paris .
199-0
294
3'33
Paris (underground)
4'8
70
o'43
3H'3
690
io'6o
The total capacity is thus 5*30 microfarads, and the
resistance 1,380 li.
In the lines from Manchester to London there
are lines of different weights, from 300 Ibs. to
600 Ibs. per mile. The " standard cable "
employed as a unit consists of an air-space paper
cable with a loop resistance of 88 ohms per mile,
and an average mutual electrostatic capacity of
054 microfarad per mile between wire and wire of
one pair. The 300 Ibs. overhead wire may be
said to be about eleven times as efficient per mile
for telephone work as the standard cable, the
600 Ibs. line about sixteen times. The wire to
wire capacity of the overhead lines (300 Ibs.)
CURRENT ATTENUATION 113
is "00918 microfarad, the capacity of a wire to earth
'0153 per mile.
If we compare a mile of the submarine cable with
a mile of the overhead as above, the capacities are
roughly as 0*24 to '0245 ; and there being twenty-
three miles of cable in the Paris -London line, it
will be seen that the difficulties of working over
it are considerably greater than those experienced
in our own country.
In the case of an alternating current passing
through the lines, there is a definite attenuation
factor according to Pupin = e~P m , where e is the
base of Naperian logarithms, /3 the attenuation
constant, and m the mileage. /3 is the fraction of
the current at any moment lost in the passage of that
current through a mile of line. The current em-
ployed in the telectrograph is, as already ex-
plained, of a character somewhat comparable with
an alternating current, but with a continuous cur-
rent impressed on it. How far these figures are
applicable to the photo-telegraphic work remains
to be found ; the contrary current used in the telec-
trograph is especially a " wipe-out" current, and
prevents the latter part of each cable discharge.
The practical effect of the line capacity is to
lengthen the time during which a discharge takes
place in the receiving apparatus. Thus if one very
brief current be sent through a high -capacity line
to the receiver an ideal oscillograph absolutely
P.T. I
ii4 PHOTO-TELEGRAPHY
dead beat, for example the action would be
longer in time than the duration of closing of the
circuit at the transmitting end.
The records made with the recording apparatus
already described show that when currents are
transmitted through a line with considerable capa-
city the " teeth " widen,, and are inclined one to
run into the next. This effect is in accordance with
the results obtained on the telectrograph, which
forms a useful and very sensitive recording appa-
ratus in itself. When a series of short contacts
are made on the transmitter these should produce
short marks at the receiver, but the actual effect
is that one mark runs into the next.
What is required, then, in an ideal system is the
shortening up of these elongated impulses, so that
the effect in the receiver for current of duration t
is also of duration t. This result is obtained to a
very fair extent in the balancer already described in
the chapter dealing with the telectrograph.
The reader may possibly have thought that the
introduction of the above matter was needless in
treating the subject of photo -telegraphy, but the
leakance of long-distance lines and their capacity,
and the attenuation factor, are the three things
which chiefly decide the question : How far and
how quickly can photographs be telegraphed ?
The receiving apparatus destined for the best
work between two places A and B is usually of a
DISTANCE OF TRANSMISSION 115
different character from that suitable for two other
places C and D. In extending our work and cover-
ing very great distances we must build the appa-
ratus to suit the conditions under which it is to be
used .
I 2
CHAPTER VI.
THE TELESTEREOGRAPH OF M. BELIN THE
EARLY WORK OF BELIN CHANGES IN HIS
SYSTEM RECENT EXPERIMENTS.
ONE of the most indefatigable workers in the
field of photo -telegraphy is M. Edouard Belin, who
has been for some years actively engaged in work-
ing out a system of his own. His apparatus has
been designated the telestereograph, but as his
method of transmission has quite recently under-
gone a radical change, it will be better to describe
his first successful models by themselves.
The use of a relief photograph, in which different
tones in the image are represented by different
thicknesses of the film, to vary the amount of
resistance in an electric circuit containing a suit-
able receiver, has been referred to in the intrto-
ductory chapter, and the idea is a very old one.
But the methods employed by Belin, both in the
mechanism for varying the resistance and in the
means of reception, were very ingenious, and he
obtained some promising results over artificial lines
and loop telephone lines, which unfortunately never
seemed to surpass a definite standard attained in
1908.
BELIN'S TELESTEREOGRAPH 117
A photograph in relief is obtained by printing
from an ordinary negative upon what is termed
carbon tissue, this being paper coated with gelatine,
which is rendered sensitive to light by the addition
of a bichromate. When sufficiently exposed, the
paper is " developed " in hot water, when the
gelatine washes away from the unexposed parts, but
remains insoluble where there has been much
exposure ; moreover, in the " half-tones/' the
gelatine washes away only to an extent depending
on the amount of exposure, I.e., on the density of
Shadow Shadow faint
Middle part
tone
FIG. 54.
the negative. The relief picture, if we were to
cut a fine section transversely through the film,
would therefore appear as shown in Fig. 54.
Now let us suppose such a relief picture wrapped
round the drum DI (Fig. 55) of Belin's transmitter.
This is a heavy metal drum turning between centres,
the whole drum, etc., moving laterally so that a
stylus fixed at S traces a spiral path over the photo-
graph. Now this stylus consists in reality of a
sapphire or a hardened steel point fitted to the end
of a rod attached to a long arm movable about F,
the fulcrum. The diagram is not flrawn to scale,
S being actually close to the fulcrum. When a
n8
PHOTO-TELEGRAPHY
high relief in the photograph happens to be at the
point S the stylus is pressed outwards an amount d,
so that the small platinum wheel W fixed at the end
of this arm is displaced an amount d X M, if the
distance from F to R be M times as great as that
from S to F.
The movement to and fro of this little wheel is
therefore always in accordance with the relief of
FIG. 55.
the photograph. It travels over a very small
rheostat, consisting of several coils of different
resistances, one end of each coil being soldered to
a thin copper plate, the other end to one unit of
the telephone line. These copper strips arc each
separated by a narrow strip of insulating material,
and the top surface worked dead flat, so that the
wheel W travels backwards and forwards over
them ; the surface of this rheostat should in reality
BELIN'S RECEIVER 119
lie along the circumference of a circle whose centre
is F and radius FW.
The top of the metal arm FR is joined to the
other wire of the telephone line ; the function of
the Belin transmitter is thus to send into the line
a practically continuous current which varies in
intensity owing to the wheel W being in contact
with a resistance coil whose resistance is in accord
with the amount of relief at each instant at the
stylus S.
This varying current (continuous because the
rheostat strips are so close together that the wheel
is always in contact with two or more adjacent
strips) is utilised at the receiving station to form
a photographic image.
For this purpose Belin employs an oscillograph
of the Blondel pattern, which consists of two fine
wires stretched across the field of a fairly powerful
electro -magnet. The current passes down one
string and up the other, not through both in the
same direction as in the case of Korn's string
shutter galvanometer ; hence, owing to the torque
produced, the wires (AB in the figure) twist the
small mirror M attached to them at the centre.
To make the damping factor e~ kt as great
as possible, the moving part works in oil, but
though this damps down the vibrations set up owing
to the inflow of a sudden current, it^must necessarily
reduce the sensitiveness. This reduced sensi-
120 PHOTO-TELEGRAPHY
tiveness is not of great consequence, because the
change in intensity of the current is not very rapid
nor periodic as it is in the case of the transmis-
sion of a single-line half-tone photograph. But it
renders the obtaining of very fine details uncer-
tain, one merging into the other or being lost
altogether. It is of course possible to increase the
sensitiveness of the galvanometer by using a more
powerful magnetic field, and by using longer wires,
but where oil is used in the latter case there would
be more friction owing to increased field of sur-
face tension, and I think that eventually M. Belin
will be obliged to utilise the methods of damping
the vibrations that have been applied to the string
galvanometer in place of oil.
Now let us see how the photographic image is
formed. A Nernst lamp N (Fig. 55) is placed
at such a position that a pencil of light con-
centrated from it upon the mirror M is reflected
upon a diaphragm G. This diaphragm has a
rectangular aperture, so that the light reflected
from M on to it when M is in the zero position
falls upon one end of the aperture ; as the mirror
swings to one side, so the light falls more towards
the other end of the aperture, etc. Now this
aperture, which had much better have been a
triangular one as Korn uses in his selenium
machines, is covered with a graduated sheet of
glass, which Belin terms his " scale of tints." It
PRACTICAL EXPERIMENTS 121
is merely a photographic negative having practi-
cally no silver deposition at one end of the rect-
angle, and graduating to a dense deposit at the
other end. As the mirror swings to one side,
so the light from it falls on a denser portion
of the scale of tints, and less light emerges from
the glass.
Behind the diaphragm is a condenser C, which
refracts the collected light and brings it to a point
on the drum D%, round which a sensitive film is
wrapped. The intensity of this spot of light is
proportional to the current, hence inversely to the
relief in the photograph. The drum D 2 travels
sideways as it revolves, the pitch of thread used
being the same as that in the transmitter. It
travels in a light-tight box fitted with a tube and
diaphragm, as in the case of the telautograph. But
M. Belin has happily arranged that the one
cylinder serves both as transmitter and receiver.
In 1907 and 1908 Belin made various experi-
ments over a long-distance telephone line, with the
two apparatus in one room under observation.
Thus he had two lines between Paris and Lyons
linked up at Lyons, the two machines being at Paris,
and the current had therefore to travel to Lyons and
back while passing from the transmitter to the
receiver.
His method of synchronising differs little from
that already described, but in the most recent
122 PHOTO-TELEGRAPHY
models he has arranged that the cylinders may be
driven at one of three different speeds, so that the
transmission can be effected rapidly or slowly as
desired. This is a very useful feature for experi-
mental instruments.
The method of employing a rheostat and travel-
ling wheel has now been more or less abandoned,
and he has adapted to the instruments a special
form of microphone, which has given some remark-
ably good results over artificial lines, I.e., under
laboratory conditions.
It is of course well known that if a diaphragm of
iron be fixed near the poles of a magnet, the mag-
netic lines of force pass through the diaphragm.
If the diaphragm be brought nearer to or further
from the poles, a change in the magnetic field takes
place. If small coils be wound round the pole-
pieces and connected in series with each other and
with a battery and telephone, then any shift in the
position of the diaphragm will be noticed by a
sound in the telephone. Belin conceived the idea
of making the stylus press against the diaphragm
of the microphone, so that the pressure on it would
vary in accordance with the relief in the photo-
graphic image ; this would vary the magnetic field
and so change the power of a current of electricity
passed through the microphone in series with a
battery and the two wires of the Blondel
oscillograph.
MICROPHONE TRANSMITTER 123
It will at once be seen that in this procedure we
are dealing with currents of very low magnitudes,
and Belin found that considerable modification of
his apparatus was necessary. In the first place the
relief in the photographs as used for his original
machines was much too great, and whereas very
thickly -coated tissue difficult to print and slow to
dry had been at first used, he now uses very thin
tissue, so that the different thicknesses of gelatine
which correspond to different tones are very minute.
If we take the curve showing the relation between
the distance of the microphone diaphragm from the
magnet poles and the current strength at the
receiver, it is found that only a short portion of
such curve is suitable for the system, and much
variation (and hence much thickness of film) is
impossible in the position of his diaphragm. The
microphone used is a large form of carbon instru-
ment, in which the pressure of the diaphragm on
three carbon balls varies their resistance, and
therefore the strength of the current flowing
through the circuit. With a large instrument of
this type he can allow of much greater variation in
the position of the diaphragm than is usual in the
diaphragm of an ordinary telephone ; the latter,
measured at the centre, being something like io~ 6
cm. for a just audible sound.
By making use of a bridge arrangement, the
balance of which is upset by the alteration in resist-
I2 4
PHOTO-TELEGRAPHY
ance of the carbon balls, Belin proposes to telegraph
pictures over long distances with his modified appa-
ratus, using a Blondel oscillograph of heavier type
as regards field magnets, and a lighter suspension
for the mirror. This could be turned through a
greater angle for a given current if the wires to
FIG. 56. Photograph transmitted by M. Belin's Telestereo-
graph, over an artificial line.
which it was attached were increased in length and
their tension lessened, but the period of swing
would be greater.
M. Belin has obtained some good results with
his system, an example of which Is shown in
Fig. 56. The results are, however, characterised
by a soft diffused appearance, which is not always-
TRANSMITTING LINE SKETCHES 125
a disadvantage. For the telegraphy of line draw-
ings/ pen-and-ink sketches, etc., he employs a
much simpler arrangement than the microphone,
a diagram of which is given in Fig. 57. A
metal arm FM is placed so that it can turn
about F, and it has a stylus S that presses lightly
against the transmitting drum. The line pic-
ture is prepared by the carbon process, and each
line is in high relief. When a line comes into con-
FIG. 57.
tact with the stylus the arm FM is pushed out-
wards, and the two platinums /?, p are thrown out
of contact. This breaks the electric circuit, and
current no longer flows into the line to the re-
ceiver. It is claimed that this method is particularly
suitable for the transmission of writing or printed
matter, and might prove of value for international
banking purposes, etc. Such a transmitter is of
course only an alternative to the Casselli trans-
mitter, as used in the Korn telautograph and the
126 PHOTO-TELEGRAPHY
author's telectrograph, and is not so practical, since
the figure of merit of the contact breaker would
require to be very high indeed to enable it to
compete with the metal stylus tracing over a
flush surface.
The synchronising arrangements, motors, etc.,
used in the telestereograph are so similar to those
already described that any further reference to them
is unnecessary. It may be said in conclusion, how-
ever, that M. Belin has found one solution to the
problem of photo -telegraphy which may prove
important when further matured.
CHAPTER VII.
THE TRANSMISSION OF PHOTOGRAPHS AND
PICTURES BY WIRELESS TELEGRAPHY.
ANY attempt to solve the somewhat delicate
problem of transmitting photographs by " wire-
less "may at first sight seem unnecessary. But it
remains to be seen whether, for long-distance work,
it will not prove both more rapid and less expensive
than transmission by cable, especially where much
water intervenes as between America and Ireland
or this country. As seen in Chapter V., the
capacity of underground cables is very great as
compared with ordinary overhead wires, besides
which, between America and England, either two
cables would be required, or one and an earth
" return." The former would be extremely costly,
and the latter would render necessary apparatus
of a very delicate and sensitive character.
The prospects opened up by a wireless method
of transmission are, on the other hand, of an
encouraging nature, as not only could long dis-
tances be covered at a high spaed, but photo-
graphs of criminals could be telegraphed to ships
128 PHOTO-TELEGRAPHY
fitted with a receiving apparatus, and sketches or
plans could be transmitted between different
sections of an army.
Mr. Hans Knudsen was the first to demonstrate
a wireless apparatus, and I have since effected
satisfactory transmissions by two new methods,
which would be possible in actual practice over
considerable distances, the latter method when
developed being, in the opinion of some of our
best wireless experts, capable of working across
the Atlantic. The scheme of Knudsen would
not, in my opinion, be practicable over any dis-
tance, for reasons that have been made clear by
experiments carried out in my own wireless work.
Knudsen employed a flat plate on which a sketch
in raised lines or a photograph in which the dark
parts were resolved into lines in relief was placed.
This travelled up under a style and back again, each
upward travel being a fraction of an inch to the side
of the previous one. A metal stylus was fixed over
the flat plate, and this, by grazing against the raised
parts of the picture, interrupted the primary of an
induction coil, whose secondary was arranged with
a spark gap. A coherer was used as the detector,
and this was continuously decohered by a striker
driven at a high speed by means of a small electro-
motor ; the coherer actuated a relay which caused
a pointed metal stylus to dig into the surface of
a glass plate coated with lampblack an image of
KNUDSEN'S APPARATUS 129
scratches was thus produced,, which could be printed
from like an ordinary photographic negative.
The synchronising was effected by the smoked
glass plate throwing out the stylus circuit at each
end of its travel and switching in another circuit
which released it and set it free to travel again.
The results were crude and streaky in appearance.
Mr. Knudsen gave some demonstrations in 1909
at the Hotel Cecil, and transmitted a picture of
the King, by his wireless machines, across the
room in which the apparatus was displayed.
Like most workers who begin their wireless
studies on a modest scale, I used a coherer in the
early experiments in order to detect the signals
transmitted from the sending apparatus. These
signals are of course regulated by the lines or dots
of which the photographic image is composed, and
the lines in a line drawing or half-tone photograph
really act as the interruptors of the primary circuit.
It will be more convenient to describe briefly one
or two of the ordinary methods of wireless tele-
graphy, as the description of the photo -telegraphic
apparatus will then be clearer to those whose work
does not carry them into the " realm of wireless."
If we take an induction coil as shown in Fig. 58
and apply a suitable battery to the primary winding,
the current of which can be rapidly interrupted by
means of an interrupter I, a spark will pass between
the terminals P, P of the secondary coil. If now we
P.T. K
130
PHOTO-TELEGRAPHY
shunt these with a capacity K and an inductance X,
and bring the spark balls P, P hear together, the
spark becomes very intense, and electrical oscilla-
tions are set up, the frequency of which is given by
the expression
n =
where n is the frequency and L is the inductance
FIG. 58.
measured in centimetres, and C the capacity in
microfarads.
If now we use the inductance X as the primary of
a small transformer, and the secondary Y is placed
between a connection to earth E and the aerial wire
or wires of the antenna A, and the oscillation fre-
quency of the aerial circuit tuned to that of the
spark gap circuit, we have a transmitting station
WIRELESS SIGNALS 131
suitable for sending signals by wireless. If the
current applied to the primary of the coil B can be
interrupted by a Morse key, then by tapping for
long and short periods we send out trains of damped
waves for long and short periods respectively,
which correspond to the dashes and dots used in
the Morse code.
Now in wireless photo -telegraphy our trans-
mitting machine clearly takes the part of the
Morse key, and just as a sentence of words and
letters can be made up of dots and dashes, so a
photographic image is constructed of long or
short marks in proper sequence on the receiving
drum of the telectro graph.
In a simple receiving circuit we have the aerial
antenna A and earth plate E connected with the
ends of a coil X placed close to another coil Y of
very fine wire, which latter transmits the wireless
" oscillation " through a condenser K into the co-
herer C. A battery B and relay R are also in series
with the coherer, which becomes conductive when
the aerial receives an electro-magnetic-wave. The
relay is thus actuated, and, by means of a local
circuit closed by it, a small electro - magnetic
hammer is made to tap the coherer, which then
becomes non -conductive again, so that the relay
contact is unmade.
t
An ordinary form of coherer is an exhausted
glass tube, in the centre of which are two silver
K 2
132
PHOTO-TELEGRAPHY
plugs near together, a part of the intermediate
space being filled with silver and nickel filings.
When a current is received these filings cohere and
make tolerable contact, so that the wires connected
to the silver plugs will convey a current. The co-
hesion requires then to be destroyed by a tap or
knock, when the coherer again becomes a sensitive
FIG. 59. Diagram of Marconi's Electromagnetic
Detector.
detector. A far more satisfactory arrangement
devised by Marconi for detecting the signals is seen
in Fig. 59. Here a string made of fine soft-iron
wires travels round two discs D, D, which are
actuated by clockwork. A glass tube fits over a
small portion of the travelling wire, round which is
wound a fine wire coil, the ends of this coil being
connected to the antenna and earth plate respec-
tively. A small secondary coil S wound over the
FIRST APPARATUS
133
primary S goes to a sensitive telephone T. Two
horseshoe magnets are placed as shown in the
diagram, with similar poles together, and as the
wire string travels past them the magnetism induced
is retained by hysteresis, this being immediately
destroyed by the passing of the wireless oscilla-
tions through P, the magnetism shifting back
FIG. 60. Arrangement first used by the Author for the
wireless transmission of pictures.
again to the normal position. This change of the
induced magnetism with respect to the magnets
causes a sound in the telephone, which is suffi-
ciently sensitive to respond to currents of io~ 13 ampere
and less.
The first wireless pictures transmitted with any
success and I am speaking of success from an
experimental point of view were obtained with the
i 3 4 PHOTO-TELEGRAPHY
apparatus shown diagrammatically in Fig. 60.
The left-hand side shows the transmitter, the right
the receiving arrangement.
D is the drum of a telectrograph as described in
Chapter IV., the stylus tracing over a sketch drawn
in insulating ink on a sheet of lead foil ; D and
the style had a condenser shunted across to prevent
sparking. The current from the battery A was
interrupted by the lines of the picture, the mag-
netism in M being thus intermittent. The relay at
M broke the contact of the battery B in circuit with
the primary P of an induction coil, S being the
secondary, electrical oscillations being set up in the
manner already described.
A negative print was used on the drum D, so that
sparking between the balls took place only when a
" line " in the picture was in contact with the stylus.
The capacity K and inductance J in the oscillatory
circuit could be adjusted, and for long distances
the aerial and earth would be connected inductively.
A short wave of about 40 metres was em-
ployed, this being determined by the expression
- = , ) where v = 3 X io 10 cm.
* v capacity inductance
= the velocity of electro-magnetic oscillations, and
A is the wave-length.
Turning now to the receiving circuit the aerial
and earth were connected to the primary of a
' jigger," the current being transformed down by
FIRST EXPERIMENTS
135
the secondary, and passed through the coherer with
a condenser K in series. A rather insensitive relay
FIG. 61. Sketch of head and shoulders of a
lady. Transmitted by wireless.
of the telephone service pattern was inserted in the
coherer -battery circuit, the battery consisting of
two dry cells. The local circuit of this relay
actuated a second relay through another battery of
136
PHOTO-TELEGRAPHY
two dry cells, and the local circuit of this second
relay included the receiving circuit of the telec-
trograph, as shown in the diagram.
The use of a contrary current running through
the receiver was necessary to render the marks clear
and short.
A local shunt circuit was also used from the first
relay to actuate the decoherer, which consisted of a
To Aerial
To Earth
FIG. 62.
very lightly built electro -magnetic striker which
tapped the coherer. This decohesion was later
effected in a much simpler manner, the act of
striking the coherer closing a local circuit which
produced an electrolytic mark on the paper of
the receiving drum.
In the figure,, EE is an electro -magnet, the
windings in series with the battery Y, and the
COHERERS
137
local side of the relay R. The coherer AB was
fixed in rigid supports,, and to one end was attached
a fixed brass collar fitted with a platinum pin P,
the magnet armature MN consisted of a piece of
iron tape fitted to an aluminium rod ending in a
piece of spring brass fixed to the pillar K. The
striker was fitted to the end of this light rod and
when it struck, the force of the blow was taken off
owing to its ability to work back through a hole
in the rod, the spring Q keeping it normally
in a fixed position. When the platinum pins
touched, the force of impact decohered the coherer,
and also completed the circuit of the electrolytic
receiver. In this way I was able to get a very
precise movement, in which one short wave train
caused one tap ; hence one mark was made on the
telectrograph paper for one dot or " contact " in
the transmitter.
The " stickiness " of coherers, however, renders
good synchronising difficult, and a straight line
would always appear somewhat wavy in the re-
ceived picture. Moreover, if the apparatus were
working with certainty, rapidity was impossible,
and after making various interesting records, the
work was continued on other lines.
I will now proceed to describe the most recent
wireless methods which promise to give more satis-
factory results, especially as original experiments
make it probable that half-tone photographs will
138
PHOTO-TELEGRAPHY
be transmitted at a considerable speed with the
apparatus.*
The transmitting apparatus consists, as before,
of a metal drum revolving under a stylus, a metal
foil print, the image of which consists of glue or
shellac lines, being wrapped round it. The battery
FIG. 63. Quartz string and selenium cell arranged for
receiving and transforming up electrical oscillations.
current flows through the cylinder, picture, and
stylus to a very lightly-built relay capable of work-
ing at a high speed ; this relay in turn actuates a
heavier one which causes the interruptions in the
primary of the alternator or induction coil. If a
coil be used, a turbine or other mercury brake is
essential.
Prov, Patent 361/10,
A RECENT RECEIVER
139
The oscillations are transformed at the receiving
station and the secondary of the transformer is
connected to a valve receiver (Marconi), this in
turn being connected with a battery E and the
FIG. 64. Sketch of the King
transmitted by the Author's
wireless apparatus.
string AB of a large galvanometer. The construc-
tion of the galvanometer is somewhat similar to that
of Korn's modification of the Einthoven instrument,
already described at some length. The " string "
AB is in this case, however, a qua?tz fibre, silvered,
about i^Jooth inch in diameter. It is free to move
140 PHOTO-TELEGRAPHY
laterally in a very powerful magnetic field, and a
current of io~ 8 amperes will displace it to a con-
siderable extent.
Light from a powerful but steady arc L passes
through the condensing lens C so as to form a
shadow of the wire AB upon a fine metal slit H.
When a current passes through the wire and causes
it to shift, the slit is uncovered, and light passes
through and illuminates a very sensitive selenium
cell SS. A weak current passes through this cell
from the battery EI into a sensitive relay R, which
also has a high speed of working. When the sele-
nium cell is feebly illuminated, its resistance drops,
and the current is sufficiently increased to actuate
the relay. The local circuit of the relay includes a
battery of about 20 volts and the telectrograph
receiver O, a contrary current being passed through a
resistance into it also, as a shunt in the manner
indicated in the diagram.
As the image is visible, being received by the
electrolytic method, it is not necessary to have any
synchronising gear on the receiver. A datum line
is drawn right across the picture being transmitted,
and near the commencement. The reproduction of
this line is carefully watched during the reception,
and the line is made to lie close against a line
drawn across the electrolytic paper. If the line
being received diverges from the drawn line then it
is known that the receiving drum is travelling either
A RECENT RECEIVER. 141
too quickly or too slowly, and the motor is regulated
accordingly.
It will be seen that the wireless transmission of
pictures requires both delicate adjustment, and
accurately -built driving machinery. We are
depending on a movement of about the five-thou-
sandth part of an inch for our recording, and there
are a number of pieces of delicate apparatus, all
reciprocative, which require to- be in perfect
harmony.
In all such work as this results can only be
obtained slowly, and progress is often only apparent
to those actually in touch with it. Time alone will
show to what extent wireless photo -telegraphy will
be of value.
INDEX
A.
ADJUSTMENTS of telectrograph,
94
Advantages of photo-telegraphy,
75
Alphabet system of transmis-
sion, 2
Amstutz, 4, 8
Aperture, triangular of receiver,
37
Artificial line, 105
Attenuation constant, 113
Ayrton, 105
B.
BAIN'S, chemical telegraph, 20
Bakewell, 2, 88
Balancing of line, 92, 96
Baudot induction, 54
Belin, M. Edouard, 116
Belin's transmitter, 117
for line drawings, 125
s with microphone, 122
Berjeanneau, 14
Berlin, experiments with, 48
Bernochi, wireless apparatus, 14
Bidwell, Shelford, 4
Blondel, 119
c,
CAPACITY, effects of, 95, 96, 108.
H3
wire to earth, 113
Carpentier, M. J., 49
Caselli, 12
Caselli's pan-telegraph, 10
stylus, 89
transmitter, 61
Charbonelle, 12, 14
Chatenet, 19, 49, 76
Chemical receiving paper, 96
Condenser, in line balancer, 101
Contrast in pictures, 51
Counterbalancing line effects, 99
Criminalistic possibilities, 59
D.
Daily Mirror, 12, 18, 49, 56, 74
Damped oscillations, 83
Damping factor, 119
of galvanometer
strings, 69, 85
Direct engraving by telegraphy,
8,9
Distortion of image, 95
counteraction of, 95
Duddell, 82
Duplex working of telautograph,
79
E.
EARTH " return," 74
Einthoverf galvanometer, 36, 61,
64, 82
144
INDEX
Electrolytic receiver, 91
Elongation of pictures, 42
Engraving, direct telegraphic,
8,9
F.
FASHION pictures, 77
Fatigue of selenium, 46
Fire at Paris telephone ex-
change, 56
First photograph wired to Lon-
don, 50
Franco-British Exhibition, 56
Frequency meter, 42
G.
GALVANOMETER, current, 80
Korn's, con-
struction of,
34
wire, lateral
displace-
ment, 35
Gamble, Mr. Wm., 8
predictions, 19
Glatzel, Dr., 48, 72
Grand National race, 74
Grzanna telautograph, n
H.
HARTMANN - KEMPF frequency
meter, 42
Haselden, Mr. W. K., 12
Heaviside, 95
I.
Illustration, 48, 72
Imperial International Exhibi-
tion, 97
Inductance of line, 95
Induction effects, 54
Installation described, 57
Iridium stylus, 65, 92
J-
JIGGER, in wireless apparatus,
134
K.
KNUDSEN, Mr. Hans, wireless
apparatus. 128
Korn, Prof. A., 7, 62, 66
photograph of,
46
Korn's compensation method, 29
galvanometer ; photo-
graph, 38
receiving apparatus, 33
selenium transmitter, 24
telautograph, 61
L.
LEAKANCE, 53, 95
Line balancer, 89, 92
Line photographs, 102
Lined appearance of photo-
graphs, 51
Lines, telephone, resistance, etc.,
of, 108
weight of, 112
Lokal Anzeiger, 49, 72
M.
MAGNESIUM shutter. 34
Manchester Courier, 57
Matin, Le. 72
INDEX
145
Meyer, n
Microphone, use of, 14
Morse induction, 54
Motive power, 64
N.
NEGATIVE photographs for
transmission, 102
Nernst lamp, 24, 33, 68, 120
o.
O'MEARA, Major, 49
Oscillograph, Blondel, 119
Oscillographic records, in
P.
PAPER, conductive, 98
Perry, Prof., 4
Photographs, half-tone, 99, 101
single line, 103
Polarisation receiver, 17
Postal strike in Paris. 73
Pupin, 113
R.
RECEIVING apparatus, Korn's
telautograph, 67
Regulating resistance on re-
ceiver, 68
Regulator of Thorne-Baker
telectrograph, 94
Relay, polarised, 44
Relief photographs,
transmit
ting, 9
used by
Belin, 116
Retouching, 58
Reversing gear, 70
P.T.
Rheostat, Belin's, 118
Ruhmer, Dr., 32, 60
s.
SANGER-SHEPHERD, 65, 72, 89
Scale of tints, 'Belin's, 120
Selenium, 4, 22, 24
colour sensitiveness
of, 32
inertia of, 26
Korn's compensation
for inertia, 26
Sharman, 16
Shunt resistance, 36
circuit on line, 93
Siemens and Halske relay, 44
Snapshots, telegraphy of, 61
Sodium sulphate cells, 66
Standard cable, 112
Stylus, construction of, 65
iridium, 65, 92
sparking at, 66
Submarine cable, 113
Switchboard, 45
Synchronising of apparatus, 36,
39- 89, 98
T.
TANDY, Mr. F., 49
Telautograph, Korn's, 61
principles of, 63
receiving on pho-
tographic
paper, 78
Telectrograph, receiver, 93
as recorder, 114
Telegraphy, duplex system, use
of, 107
Telestereograph, Belin's, 116
146
INDEX
Telewriter, n
Thorne-Baker telectrograph, 88
Transatlantic possibilities, 60
Tucker, Mr. A. H., operating
Korn's telautograph ; photo-
graph, see Frontispiece
Typewriting, transmission of,
w.
WAVE-LENGTH, effect on inertia
of selenium, 32
Wheatstone bridge, 30
Belin's use
of. 123
Will, Herr, 48
Wipe-out current, 113
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