AN IMPROVED MODE OF CORRECTING THE DEVIATION OF COMPASSES IN IRON SHIPS AND OF CONSTRUCTING SHIPS' COMPASSES
Year: 1866

page_text: LETTERS PATENT to Evan Hopkins, of Clarendon Gardens, Maida
Hill, in the County of Middlesex, Civil Engineer, for the Invention
of "AN IMPROVED MODE OF CORRECTING THE DEVIATION OF COMPASSES IN
IRON SHIPS AND OF CONSTRUCTING SHIPS' COMPASSES."
Scaled the 20th July 1866, and dated the 23rd January 1866.
PROVISIONAL SPECIFICATION left by the said Evan Hopkins at the
Office of the Commissioners of Patents, with his Petition, on the
23rd January 1866.
I, EVAN HOPKINS, of Clarendon Gardens, Maida Hill, in the County of
3 Middlesex, Civil Engineer, do hereby declare the nature of the said Inven-
tion for "AN IMPROVED MODE OF CORRECTING THE DEVIATION OF COMPASSES IN
IRON SHIPS AND OF CONSTRUCTING SHIPS' COMPASSES," to be as follows:-
This Invention relates, firstly, to certain means of removing the main
cause of the deviation of the mariners' compass in iron ships, namely, the
O polarity of the vessel. This polarity is acquired while the ship is building,
or it may be induced by repairs, by firing, or otherwise, and I now propose
to destroy it by passing electric currents (by the aid of a powerful electro-
magnetic battery) through the hull. A convenient way of forming the
electro-magnets is to fix two pieces of soft iron (covered with coils of

page_text: insulated copper wire) one at the bow and the other at the stern of the
vessel, and to connect the opposite ends of the coils with the poles of the
battery and with the hull of the ship. I pass currents by means of this
apparatus through the hull of the vessel to and fro, from bow to stern and
from stern to bow, for about 20 minutes more or less, the effect of which
is, first, to change or reverse the induced polarity, then to neutralize and
finally to destroy the polarity of the ship. Large iron vessels, such as
those in use in the Royal Navy, should have permanent pieces of soft iron
covered with copper coils screwed to the bow and stern, so as to provide
for destroying or neutralizing at any time polarity which may be induced
through the practice of firing or any other causes. In those vessels
which are furnished with galvanic batteries for conveying orders from the
captain to the steersman the same batteries and wires will be available for
destroying the polarity of the hull when required. To vessels thus
treated I propose to apply the steering compass out of range of the attrac-
tion of the surrounding iron. To this end I mount it on a pillar or other
fixed support from 10 to 20 feet above deck and from the steering gear.
In order that the compass card may be clearly seen and read by the
helmsman at the distance required I place a reflector near the card, and at
such an angle as will exhibit the card vertically like the dial of a clock.
The compass dial will of course require to be illuminated at dusk, all
night, and in dark foggy weather. From the course which the magnetic
current takes, passing out from the southern hemisphere and entering at
the northern hemisphere, ordinary compass needles have a great dip when
approaching either of the earth's poles, and they thus lose much of their
force and are often little to be relied upon excepting within a very narrow
zone near the equator. In order, therefore, to ensure correctness, steady
vibration, and to avoid excessive oscillations in stormy weather, I form the
needles of thin bars of metal set edgewise and of a curved or bent
figure, thereby depressing the poles to any required degree suited to the
parallel of latitude in which they are to be used. Two of these needles I
brace together by a central bar which is fitted with the agate cup or
centre for the fulcrum pin to work in, and over these needles I place the
compass card. To avoid mistakes in steering from verbal directions I
propose to fix a dumb card in front of the binnacle for setting the course
for steering.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent,
filed by the said Evan Hopkins in the Great Seal Patent Office
on the 23rd July 1866.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, EVAN
HOPKINS, of Clarendon Gardens, Maida Hill, in the County of Mid-
dlesex, Civil Engineer, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Twenty-third day of January, in the year of
our Lord One thousand eight hundred and sixty-six, in the twenty-ninth
year of Her reign, did, for Herself, Her heirs and successors, give
and grant unto me, the said Evan Hopkins, Her special licence that
I, the said Evan Hopkins, my executors, administrators, and assigns, or
such others as I, the said Evan Hopkins, my executors, administrators, and
assigns, should at any time agree with, and no others, from time to time
and at all times thereafter during the term therein expressed, should and,
lawfully might make, use, exercise, and vend, within the United Kingdoni
of Great Britain and Ireland, the Channel Islands, and Isle of Man, an
Invention for "AN IMPROVED MODE OF CORRECTING THE DEVIATION OF COMPASSES
IN IRON SHIPS AND OF CONSTRUCTING SHIPS' COMPASSES," upon the condition
(amongst others) that I, the said Evan Hopkins, my executors or admi-,
nistrators, by an instrument in writing under my, or their, or one of
their hands and seals, should particularly describe and ascertain the
nature of the said Invention, and in what manner the same was to be
performed, and cause the same to be filed in the Great Seal Patent Office
within six calendar months next and immediately after the date of the
said Letters Patent.
NOW KNOW YE, that I, the said Evan Hopkins, do hereby declare
the nature of my said Invention, and in what manner the same is to be
performed, to be particularly described and ascertained in and by the
following statement, reference being had to the Drawing hereunto annexed,
and to the letters and figures marked thereon (that is to say) :—
The deviation experienced in iron ships of the mariners'
compass, which
deviation is the cause of great perplexity and much risk to navigators,
arises from three causes; first, from the disturbing influence of the polarity
of the iron ship acquired during its construction; second, from the induced
polarity of the axle of the steering wheel and other masses of iron
employed on board ship; third, from the loss of directive power in the

page_text: compass needles, which loss increases their susceptibility to disturbing
local influences and renders them the less able to retain their normal
meridional direction.
Now the object of this Invention is to correct or remove these dis-
turbing causes. To this end I propose, first, that the iron vessel when
completed shall be depolarized and brought to the normal state of iron as
regards its attractive power; second, that the compass box with its card
and gimbal shall be placed beyond the disturbing influence of the steering
apparatus or other soft iron employed on deck; and in order that it may
be seen at a distance, say, from ten to thirty feet from the steering wheel,
like the dial of a clock, I furnish it with a reflector placed at an angle of,
say, forty-five degrees to the compass box; third, that in order to allow
the compass needles to conform to the direction of the terrestrial magnetic
force in high latitudes they are to be made of a segmental form with their
ends terminating at points that indicate the average angle of the "dip."
The depolarization of the hull of the iron vessel I effect on the same
principle as has heretofore been adopted in the depolarization of iron bars
in the production of magnets, but with the aid of batteries and electro-
magnets instead of the ordinary horse-shoe magnets.
In order that the principle of depolarization on which I proceed may be
the better understood I will first call attention to the action of ordinary
magnets.
:
In the accompanying Drawing, Fig. 'l represents a prepared magnetic
bar without polarity. Near this bar small compasses may be placed without
being affected, as indicated by the Figure. The bar is then in its normal
state. Fig. 2 shews the same bar converted into a perfect magnet by
means of a horse-shoe magnet rubbed over the bar from south to north. In
polarizing the bar due care is taken to place the south end of the horse-shoe
magnet towards the intended north end of the bar, as shewn in the Figure.
After the bar has acquired its polarity it will affect compasses placed in
its neighbourhood in the manner indicated in the diagram, and at distances
in proportion to the size of the bar. By reversing the horse-shoe magnet
and rubbing the bar a few times in the contrary direction, from north to
south, the polarity of the bar will be destroyed, as shewn in Fig. 3, where
the compasses placed near the poles remain unaffected. In like manner I
propose to depolarize iron vessels, first making, with the aid of compasses,
an accurate survey of the magnetical condition of the hulls of such vessels.
Fig. 4 represents in plan view an iron vessel thus surveyed, and shewing
the vessel highly polarized, with the north pole head acquired by reason of

page_text: the hammering to which it has been subjected during construction, and
Fig. 5 is a side elevation of the stern end of the same vessel. The influence
of this polarity (the direction of which is indicated by the arrows).extends
from twenty to thirty feet from the sides and above the deck, and especially
near the stern and the bow, see a and b, Fig. 5. Fig. 6 shews the com-
mencement of the depolarizing process on one side, from the bow towards
midship, the assumed polarity, as in Figures 4 and 5, being north.
Figures 7 and 8 illustrate the nature of the circulating action of the
magnetic currents in the common horse-shoe magnet and the coiled electro-
magnetic bar respectively. Both will act on the iron plates precisely in
the same manner. The bow of the vessel, Fig. 6, having a north pole, the
electro-magnet, Fig. 8, in order to destroy this polarity, is to be placed first.
at the head of the vessel, and the currents generated by means of the
battery are made to circulate, as shewn in the Figure, in a direction con-
trary to the acquired polarity of the vessel. The electro-magnet is now
slidden along the plates rapidly towards the stern, it being lowered at every
repetition of the traverse motion, so as to pass over and depolarize a fresh
line of plates. When time is an object, two or four. sets of batteries and
electro-magnets may be employed at the same time. The electro-magnet
is suspended over the ship's side by ropes pendent from the bulwarks and
held by the hands of the operator, who is on deck, and it is moved from
end to end over and in contact with the main plates of the ship, see Fig. 9.
As the electro-magnet adheres much more strongly to the plates than the
horse-shoe magnet, it requires to be liberated before it can be moved
forward; this is effected by making metallic contact between the copper
wires of the battery, and thereby temporarily destroying or enfebling the
power of the magnet. The depolarizers are thus easily moved and rapidly
along the plates, like the horse-shoe magnet along an iron bar. The upper
part of the stern of the vessel being generally more or less semicircular, a
single-acting electro-magnet should be placed in the culminating point to
act as the stern pole of the vessel until the process is completed. The
stern post will serve as the polar termination in the lower part near the
keel. In depolarizing iron vessels, and to allow for the reaction of the
iron beams on the plates, it is necessary not only to destroy the polarity
acquired by the skin of the vessel, but also to produce a weak contrary
polarity which will be absorbed or destroyed by the counter influence of
the iron beams, which are inaccessible to the operator. During the whole
of the operation he must be guided by his compass, in the same manner as
he is guided in making large magnets. A large iron ship may, with the

page_text: aid of four sets of Grove's batteries (ten cells quart size) with their con-
necting electro-magnets be depolarized in the course of a day, if the
vessel.be free from all obstructions and conveniently placed. After the
removal of the polarity of the iron hull, represented in Fig. 5, the compass
is still disturbed, as I have ascertained experimentally by the induced
polarity of the steering axle, the course of the natural currents being as
indicated at Fig. 9. The steering compass is commonly placed near the
end of the steering axle, or where the disturbance is generally very great,
as shewn at c, Fig. 9. Granting that we are able to destroy that polarity,
such a position for so important and delicate an instrument as a compass is
highly improper and dangerous, for the steering gear, unlike the hull of a
ship, is subject to constant vibration, and therefore liable to acquire the
induced polarity of soft iron. As then the steering apparatus will not
permanently remain in its normal state, like the plates of an old iron ship,
this source of disturbance must be guarded against; to do this I place
the steering compass beyond the reach of the influence of the individual
masses of iron and the ends of bars, giving it an elevation above deck
as shewn by d, Fig. 9.
Figures 10 and 11 represent in front and sectional elevations binnacles
with reflecting cards and curved needles, constructed according to my
Invention. These binnacles I place, say, from ten to fifteen feet from the
steering wheel, and as high from. the deck as the boom will admit. To
ensure still greater safety and correct steering at all times, and guard
against any changes which may occur during a long voyage, two compasses
about six feet apart should be attached to the mizen mast about fifteen to
twenty feet above deck, similar to those now used in some iron vessels, but
suspended from arms transversely of the deck and fitted with reflectors
underneath, as shewn at Figures 12 and 12*, so that the cards may be seen
from the steering wheel. By means of these arrangements the steersman
will have the advantage of a correct standard compass at all times, and
thus the errors arising from the deviation on board iron vessels will be
avoided.
My segmental needle 1 propose to cut out of flat plates of about one
twenty-fourth of an inch in thickness, and to give them a depth of about
one and a half inches. This form of needle, while it is free to "dip" under
the peculiar well-known influence of the magnetic currents in high latitudes,
will not, like the ordinary straight needle, lose its vitality (or inherent power
of indicating the true north), and it will therefore be less liable than compass
needles generally to be effected by disturbing local influences. The needles

page_text: may be mounted singly or in pairs, as shewn in the Drawing, and applied
in any approved manner for giving the compass indications.
Having now set forth the nature of my Invention of "An Improved
Mode of Correcting the Deviation of Compasses in Iron Ships, and in
Constructing Ships' Compasses, and explained the manner of carrying
the same into effect, I wish it to be understood that under the above in
part recited Letters Patent I claim,
First, removing or destroying the acquired polarity of iron ships by the
means above described.
Secondly, the application to binnacles or compass boxes of reflectors in
the manner and for the purpose above described.
Thirdly, constructing compass needles as above described.
In witness whereof, I, the said Evan Hopkins, have hereunto set my
hand and seal, the Twenty-third day of July, in the year of our Lord
One thousand eight hundred and sixty-six.
EVAN HOPKINS. . (L.S.)