The Sun.
London, England, 1858-10-06 00:00:00

TO THE EDITOR OF THE SUN.

Sir,—l am instructed to forward for pliblication
a report received yesterday from Mr. W. T. Henley,
the electrical engineer, of St. John-street, Clerken-
well, who is one of the gentlemen whom the
directors have consulted in reference to the state of
the Atlantic cable.

Mr. Henley's advice in reference to laying the
shore end at Valentia has been anticipated. From
previous circumstances it has been thought advis-
able to postpone until further information was ob-
tained the operation of laying the shore ends, with
a view to save what at the time the directors were
advised would be unnecessary expense.
The directors, however, subsequently decided,
after due reflection, that it would be advisable to
lay the Valentia shore end without delay, and a
vessel is now on its way to effect this object.

Yours truly,

GEO. SAWARD, Secretary.
Chief Office, 22, Old Broad-street, London, Oct. 5.

" Valentia, Sept. 30, 1858.
TO THE CHAIRMAN AND DIRECTORS OF THE
ATLANTIC TELEGRAPH COMPANY.

" Gentlemen,—ln accordance with your instruc-
tions, I have, since my arrival here, on the Bth inst.,
carefully tested the cable at various times, and with
different degrees of battery power, and I found its
insulation seriously impaired, and the results of the
testing lead to the conclusion that the injury is at
a considerable distance from this (very nearly 300
miles of the cable apparently intervening between
this point and the fault.)
" As I think it right you should know on what
grounds, and by., what modes of operating, I and
others have arrived at this conclusion, and as you
may also like to be informed as to some of the phe-
nomena of electrical science, as shown in connection
with this cable, I have ventured to go a little into
detail, hoping thereby to con' ey some information
that may not be unacceptable.
" On connecting one pole of a voltaic battery
with the end of the cable with a galvanometer in
circuit, and the other battery pole to earth, I find
the current meets a resistance to its passage equal
to 290 miles of the copper conducting wire of the
cable, and as the cable is more than 2,000 miles
long, it is, tfierefore, evident that the greater part
of the current finds a shorter route to the earth.

" By resistance is meant the impeding force that
electricity meets with in its passage through con-
ductors of all kinds, metallic or otherwise, and
whichvaries immensely, not only in various metallic
and other bodies, but also in the same kind of
metal, and this can be accurately measured, even
in one inch of wire. Taking any given metal, the
conductibility of which is uniform, the resistance of
the wire will be found to increase as the size de-
creases, exactly in proportion to the sectional area.
A mile of No. 40 copper wire is thus found to re-
sist as much as 175 miles of the conducting wire of
the Atlantic cable. It is necessary, also, that the
fine wire should have been previously tested with
some of the cable, as wires of the same gauge are
frequently found to vary very much in size as well
as in conductibility.
"Knowing the resistance per yard of the
fine wire, to obtain that of the cable comprised
between the point of operating and the fault
(and thus to find its length), the battery
and galvanometer are connected with the line and
earth in the before-mentioned manner; the degrees
of deflection are accurately read on the galvano-
I meter, and this process is repeated several times
with batteries of different degrees of strength ; the
batteries and galvanometer are then disconnected
from the cable and earth, and connected with coils
of the fine wire, the length of which latter is added
to or diminished until the readings of the galvano-
meter exactly coincide in every case with those
noted when connected with the cable. The length
of the fine wire will then give that of the cable up to
the point at which the battery current finds earth,
reckoning about one mile of cable for every ten
yards of fine wire. There are several methods of
doing the same thing, but they are all based on the
same system of proportionate resistances.
" There is next the resistance of the fault itself
to be taken into account, for, strange as it may ap-
pear to some, faults (in proportion to their magni-
tude) may be equal in resistance to from one mile
to several hundreds of miles of cable, and would
give the same indications on a testing instrument.
If we knew the exact nature of the injury, and how
much of the copper was exposed, we could with
tolerable certainty tell at what distance it existed ;
but, in the absence of such knowledge we must
judge from appearances, making use of any pre-
vious experience we may have had in matters of
a similar kind. And firstly, we know if much of
the resistance was produced by the fault, it must
expose a very small amount of surface, and that on
sending positive currents, the wire (by electrotypic
action) would be oxidised at the faulty spot, and
the galvanometer would show the fault was partially
repaired by the non-conducting power of the oxide.
" On reversing the direction of the current hy-
drogen would be evolved, which, by reducing the
oxide and cleaning the wire, brings the fault back
to its former state. Should it be of considerable
size, and consequently of small resistance, the coat
of oxide found would be thin, and quickly reduced,
by reversing the current, showing that very little
alteration was produced by changing its direction.
" Precisely this effect is produced by sending cur-
rents into the cable, indicating the injury to be
of that character. A small fault could not reduce
the strength of the signals to the extent we find
them, unless the wire was separated near that point,
and this (which is quite within the range of proba-
bility) would set our calculations at nought. That
the cable is not severed we have abundant proof,
but that any one can, by the most delicate tests,
discover whether the conducting wire is so or not
in a cable of this length I utterly deny. Should
such be the case, it does not follow that the line
must be rendered useless ; as I have known under-
ground-telegraphs work for months after the con-
ducting wires have been separated more than a
quarter of an inch by the decomposing power of the
batteries employed. A slight fault existed in the
gutta percha. This admitted moisture, which, by
conveying the electricity to the earth, caused the
decomposition of the wire, and then aided the
working of the telegraph, by conducting a portion
of the current from pne point of the separated wire
to the other. Signers were much reduced in power,
as in the present case ' • still the wire continued to
work, and if such can be done for months it might
happen for a longer period.
" If by any means the conducting wire separates,
and the gutta percha remains sound, all communi-
cation ceases from the absence of moisture to com-
plete the circuit. By our testing one fact is un-
questionably established, and that is, the fault is
not beyond 300 miles. I speak of the great fault.
Others may exist between that and Newfoundland;
but if it be a fact (as I have heard), that on testing
at the latter place very little earth is shown, the
probability is that the other part of the cable is
good. Having arrived at the fact of the in-
jury not being beyond three hundred miles, the
difficulty, is to know how much within that dis-
tance it is to be found, or how much of the re-
sistance is due to the cable, and how much to the
fault ; and although by accurate testings and exa-
minations a pretty correct knowledge of the facts may
be obtained, still it is liable to some uncertainty,
and instances have occurred in testing cables where
the most experienced have been quite wrong in
their conclusions.
"I cannot think it possible for the injury to be
in the harbour, but should think it advisable to lay
down some length of shore end, as the present cable
near the land must soon be injured by friction on
the rocks and shingle. A piece of the same size
laid across the harbour for the Magnetic Company
was entirely worn asunder some days since.
" In my opinion the fault or faults existed in the
cable before it was submerged, and that they would
have been detected and made good had the precau-
tion been observed of having the whole cable tested
in water during its manufacture.
" Its not showing so bad when first laid is easy
to be accounted for, as it takes some time for the
water to soak through the coating of pitch and tar.
In a cable I am now manufacturing a fault was four
days in the water before showing anything.
" Had your cable been injured after submersion
by resting on the sharp edge of a rock, the inner
wire and the outer metallic covering must have come
in contact, and that this is not the case we have ab-
solute proof, both from the fact of a battery current
being generated by the iron sheathing and the ex-
posed copper, and from signals being received ob-
served—signals were, from the first, much weaker
than they ought to have been from a tolerable in-
sulated line of that length, and were scarcely suffi-
cient to work a very delicate relay (which can be
used with a current so feeble that it could only be
detected on the tongue). The currents now received
are not more than a tenth of that power, and
can only be indicated on Professor Thomson's
very ingenious reflecting galvanometer, from New-
foundland ; for, did the iron touch the copper con-
ductor in the smallest point, not the slight(st signal
could be seen. This is constructed on the principle
of the boys' trick of receiving the rays of the sun on
a piece of looking-glass and reflecting them on a
wall, a very small motion of the hand giving a
range of many feet to the spot of light. Professor
Thomson attaches a small mirror to the magnetic
needle of a very delicate galvanometer of his own
contrivance. The light of a lamp is thrown on the

mirror, and a motion of the needle that would be
inappreciable in itself is plainly indicated by the
reflected spot of light on a scale. The apparatus
could be made much more delicate, still, and
capable of working with the smallest amount of
current, but there is an obstacle in the way of
using such a feeble power, and that is the earth-
current which shows itself at all times more or less.
" If this earth-current were at all constant in its
quantity or direction it would be quite easy to com-
pensate for it and render its effect neutral ; but it
is most erratic in its movements, sometimes throw-
ing the spot of light entirely off the scale, at others
changing from positive to negative, and back again,
so rapidly and frequently, and with such regu-
larity, that it is difficult to know whether it is New-
foundland or the earth-current signalling.
" These earth-currents in submarine and subter-
ranean lines (like the atmospheric currents, as they
are termed, in over-ground wires) are produced by
the inductive effect of natural currents of electricity
moving parallel with the conducting wires, it being
a well known law of electricity that if a current
moves in the vicinity of a wire or other insulated
conductor a current is set up in such wire in a con-
trary direction,' its strength being in proportion to
the parallelism of the wire with the natural cur-
rent.

" Any wire laid parallel with the Equator, or
nearly so, will have its electrical condition dis-
turbed by every variation in the earth's magnetism.
On the first establishment of practical telegraphy
the inconvenience experienced from these currents
was as annoying as it was unexpected, but in course
of time contrivances were produced capable
of modifying or counteracting their effects, so
that but little trouble is now felt from their occur-
rence ; although even now, occasionally, on some
lines, all communication is stopped for a short time
when these terra-magnetic currents are unusually
strong. On lines of 100 miles or so they only show
themselves at intervals ; at all other times the line
is quite free. But on a line of such enormous
length as the Atlantic cable electric disturbance is
sure to take place on some part of it at all times ;
and if a current is set in motion in any part the
effect is communicated throughout the whole. In
another cable (as well as in this, had its insulation
been more perfect) earth-currents would not cause
much trouble, as the working-currents sent through
the line would not lose their stsength, as in the pre-
sent case, and consequently would overpower them.
" The mere resistance of the cable, as regards its
length, would offer very little impediment to its
working. The same length of insulated wire
stretched on dry earth or other non-conductor could
be worked through with a very small power, and
at a rapid rate. It is only when it becomes sur-
rounded by a conductor such as damp earth or
water, or by the metallic covering of the cable, that
the phenomena of induction again come into play ;
and the more complete the insulation the greater
will be the embarrassment from induction.
" The effect of this is shown when a battery is
connected with the line and earth, or outside of the
cable. The inner or conducting wire becomes
charged or electrified plus ; the outer coating minus
(similar to a Leyden jar). When the ends are put
to earth the effect goes off, but not instantly ;
and when the two electrified media are so far re-
moved as in a line of 2,000 miles, if connected with
the earth, a very considerable time is occupied
both in charging and discharging, causing much re-
tardation of the current ; so that I think four words
per minute will be the maximum rate of trans-
mission through any Atlantic cable with the pre-
sent dot and dash system. If other plans can be
worked by which a letter would be indicated by one
or two signals the rate would be increased in pro-
portion.
"As I have made use of the terms ' resistance'
and ' retardation,' and as they are words having
different meanings, I will explain what constitutes
the difference. The ' resistance' of a wire has the
effect of keeping part of an electric current back, or
diminishing its quantity, without affecting its
velocity, the remainder passing as quickly as it
would through a wire of the same length with less
than a hundredth part, of the resistance.
" The effect of retardation,' on the contrary, is
to diminish both the quantity and the velocity of
the current. For example, in an overground well
insulated wire 2,000 miles long, an electric current
or impulse would traverse the entire length in one-
, tenth of a second; through the same extent of sub-
marine line, owing to the effect of the charge, the
time occupied would be nearly a second and a half.
"Respecting the question of injury to the line
from the use of powerful currents, if a small hole
leading to the wire exists in a gutta-percha cover-
ing, near either end, there is no doubt that a cur-
rent of great quantity and intensity (whether pro-
duced by battery or coils) would have the effect of
; enlarging the breach by burning • but this can only
' take place to a limited. extent. Heat can only be
developed by an electric current when the latter
` meets with great resistance ; consequently, so soon
E' as that is diminished by a slight enlargement of
'• the hole all burning ceases. I tried the experiment
alternately with the large, induction coils with the
battery now here (400 cells of Daniel's) and with
L my large magneto-electric machine. They were
each connected in turns with the line and earth, and
at the same time with a piece of gutta-percha
' covered wire (in which the copper was bared to 1 -32 d
! inch diameter) and a piece of copper in a basin of
- sea water, thus dividing the current between the
two routes. The coil current enlarged the fault to
' 1-20th inch in diameter, the batteries to 1-16th, both
slowly. That from the magneto made no change in
the fault it was applied to until it was disconnected
from the line and earth, and allowed the one road
only, when burning took place, as might have been
' expected. The fault was enlarged very slowly to
1-10th of an inch. On repeating this with the
coils the fault was increased to 1-10th diameter,
and with the batteries to 1-6th inch, rapidly with
both. No further burning can take place with
' either current until the wire is brought to the sur-
face of the water, when, owing to the resistance in-
creasing by the fault being only partly immersed,
the burning commences anew, and the gutta percha
inflames.
" On the arrival of my large magnetic machine I
' put it together, and connected it with the cable,
• and have used it a part of every day since, sending
sometimes reversals and at others words and sen-
tences. lam unable to tell whether they were re-
' ceived and understood, but hope to find such has
been the case on the receipt of intelligence from
Newfoundland. Having a machine at one end only
it will, of course, be evident that even if they re-
ceived properly they could not have answered
better than before. But we have been encouraged
by seeing more reversals and attempts to send words
from them lately than before. I will leave the
machine here ; it will be worked at stated hours
each day by the assistants until the days fixed upon
in October, when it will be used alternately as ar-
ranged with the battery and coils: The clerks at
' each end will then act according to preconcerted
' arrangements, which I hope will have the effect of
renewing telegraphic correspondence ; if that is not
accomplished, probably the best thing then would
be to raise the cable for about 15 miles out and test.
I cannot say I have any hopes of the fault being found
within that distance; but as it would not be attended
with any trouble or risk I think it worth the trial.
' If the injury is in the deep soundings, I believe any
attempt to raise it would be the means of break-
ing the cable and losing the end altogether. If the
state of the cable should not get worse I am still in
hopes of its being rendered workable by transmit-
ting signals slowly, by having delicate receiving
apparatus, and by adopting means for neutralising
the earth current. Prof. Thomson has partially suc-
ceeded in the latter object by throwing into the re-
ceiving end of the line feeble currents of different
values (from 1 cell to 1-20th of a cell) in opposition
to the earth-current.—l am, &c.,
"W. T. HENLEY, Telegraph Engineer.
" 46, John-street-road, Clerkenwell."