IM- PROVEMENTS IN THE MARINERS' COMPASS, AND IN APPLIANCES FOR CORRECTING ITS ERRORS
Year: 1879

page_text: LETTERS PATENT to Sir William Thomson, Knight, of Glasgow College, Doctor
of Laws, and Professor of Natural Philosophy in the University and College of
Glasgow, in the County of Lanark, North Britain, for the Invention of "IM-
PROVEMENTS IN THE MARINERS' COMPASS, AND IN APPLIANCES FOR CORRECTING
ITS ERRORS."
Sealed the 25th April 1879, and dated the 20th February 1879.
PROVISIONAL SPECIFICATION left by the said Sir William Thomson at
the Office of the Commissioners of Patents on the 20th February 1879.
Sir WILLIAM THOMSON, Knight, of Glasgow College, Doctor of Laws, and
Professor of Natural Philosophy in the University and College of Glasgow, in the
County of Lanark, North Britain. "IMPROVEMENTS IN THE MARINERS' COMPASS,
AND IN APPLIANCES FOR CORRECTING ITS ERRORS."
The objects of this Invention are,--
First. Greater steadiness of the compass card and diminished wear of the bearings
of the bowl and card in vessels where there is great vibration due to the working of
the engines, the screw, or other causes.
Second. Greater steadiness of the compass in vessels of war during gun fire.
Third. An improved method for applying correctors for the semicircular error.
Fourth. An improved adjunct for the correction of the heeling error.
Fifth. An improvement in the compass card.
Steadiness of the compass card in steamers which have powerful engines and
where there is much vibration has usually been obtained by suspending the bowl
by means of india rubber bands. One serious objection to this method is that the
india rubber is liable to become rotten when the ship goes to warm climates or has
exposure to oil. I aim at obtaining steadiness of the compass card without the use
of india rubber, and I attain this object by hanging the gimbal ring from an clastic
ring, which is supported by two balls resting in two sockets attached to the brass
rim of the binnacle. The elastic ring is made of brass wire. A single wire is first
formed into a ring of the proper size. This serves as a core on which a continuous
brass wire is laid on spirally six turns or thereabout round the core. This forms
an elastic ring strong enough to support the compass-bowl and gimbal ring. The
Price Rd 1

page_text: .
elastic ring has got two balls fixed at the ends of a diameter which rest in two
sockets attached to the brass rim of the binnacle. This mitigates the effect on the
knife edges bearing the gimbal ring and bowl, and on the point bearing the compass
card, of vertical tremors of the platform on which the compass rests. The knife
edges of the gimbal ring are supported on two grooved stirrups hung by chains from
the elastic ring. This mitigates the effect of horizontal tremors of the platform.
The semicircular error is corrected by steel magnets according to the general
principle first given by the Astronomer Royal.
The varying adjustments of the correction required for variation in the ship's
sub-permanent magnetism and magnetism induced by the vertical component of the
earth's magnetic force I effect in the following manner :-I use two sets of magnets,
one set placed fore-and-aft for counteracting the fore-and-aft component of the
ship's magnotisin, and the other set thwartship for counteracting the thwartship
component. The thwartship set of magnets consists of a number of magnetized
steel rods. The true north ends are painted blue, and the true south ends red. A
vertical row of holes bored horizontally athwartship in the binnacle, or in any con-
venient solid support under the compass constitute receptacles for holding the
magnets. A sufficient number of magnets are placed in these holes to counteract
the thwartship component of the ship's magnetism.
The fore-and-aft magnets are similar to the thwartship ones, and are placed in
holes similarly bored fore-and-aft, but I use two vertical rows fore-and-aft, one on
each side of the compass, or on one row as nearly under the centre of the compass
card as the tube for the heeling corrector allows, in order that there may be no
perceptible difference in their effect on the compass when the ship rolls or heels to
one side or the other. The holes both for the thwart-ship and fore-and-aft magnets
are bored at such distances from the needles of the compass card that the increase
or diminution of the correcting force on the compass needles caused by raising or
lowering a magnet from one hole to the next one may be the same at different
levels. The magnets are kept in position by a door or cover in the shape of a long
bar across their ends secured by lock and key.
For counteracting the part of the fore-and-aft component of the ship's magnetism
which is due to magnetism induced by the vertical component of the earth's
magnetic force, I have a receptacle fitted to the binnacle, in which a bar of soft iron
can be placed.
.
For correcting the heeling error I use an instrument- for comparing the vertical
component of the earth's magnetic force on shore with the vertical component
on board.
This is constructed as follows:-Two hardened steel wires are
joined together at their ends and are supported on two iridium points in a line
at right angles to the length of the bar, and passing as nearly as may be through
the centre of gravity of the two bars. One of these points rests in a sapphire cup,
and the other in a sapphire V. The needles are accurately balanced, so as to be
horizontal when resting on the points before being magnetized, and are then
maguetized. The needles are brought to a level position again by a vertical
magnet placed at equal distances from the four polos of the needles. This magnet
can be moved up and down by means of a screw. The position of the vertical
magnet measures the vertical force on the needles according to a scale determined
by experiment.
The improvement in my compass card is for the purpose of preventing the ends
of the needles from catching the silk spokes if the card is thrown up from concus
sion while guns are being fired. I accomplish this by connecting the ends of the
needles with a silk cord passing through holes drilled in their ends.

page_text: -
DI
GATION in pursuance or the conditions of the Letters Patent filed by
the said Sir William Thomson in the Great Seal Patent Office on the 20th
August 1879.
Sir WILLIAM THOMSON, Knight, of Glasgow College, Doctor of Laws, and
Professor of Natural Philosophy in the University and College of Glasgow, in the
County of Lanark, North Britain. "IMPROVEMENTS IN THE MARINERS' COMPASS,
AND IN APPLIANCES FOR CORRECTING ITS ERRORS."
The objects of my said-Invention are as follows:-
Firstly. To obtain greater steadiness of the compass card and diminished wear of
the bearings of the bowl and card in vessels in which there is great vibration due
to the working of the engines, the screw, or other causes; and,
Secondly. Greater steadiness of the compass in vessels of war during gun fire.
Thirdly. An improved method of applying correctors for the semicircular error.
Fourthly. An improved adjunct or auxiliary instrument for the correction of the
heeling error.
Fifthly. An improvement in the compass card.
To produce such steadiness of the compass card as has hitherto been obtained in
steamers which have powerful engines, and where there is much vibration it has
been customary to suspend the bowl by means of india rubber bands. A serious
objection to this method is that the india rubber is liable to become rotten by
exposure to heat or oil.
According to my Invention I obtain a greater degree of steadiness of the compass
card without the use of india rubber, and this I effect by hanging the compass bowl
either directly or with the intervention of a gimbal ring from an elastic metal ring,
preferably of brass wire, and constructed as follows:-A single wire is first bent,
and its ends are united by soldering or brazing, so as to form a ring of the proper
size. This serves as a core on which a second brass wire is laid on spirally, six
turns or thereabout, round the core. The ends of this second wire are also united
by soldering or brazing, and thus an elastic ring is produced strong enough to support
the compass bowl. In the case of suspending the compass bowl from the elastic
ring with the intervention of a rigid gimbal ring, the said elastic ring has two balls
fixed at the ends of a diameter, which balls rest in two sockets attached to the brass
rim of the binnacle, or the sockets may be on the ring and the balls on the binnacle
if preferred. This arrangement mitigates the effect on the knife edges bearing the
gimbal ring and bowl, and on the point bearing the compass card of vertical treinors
of the platform on which the compass rests. The knife edges of the gimbal ring
are supported on two grooved stirrups hung by chains from the elastic ring. This
mitigates the effect of horizontal tremors of the platform.
The semicircular error is corrected by steel magnets according to the general
principle first given by the Astronomer Royal. The varying adjustment of the
correction required for variation in the ship's sub-permanent magnetism and
magnetism induced by the vertical component of the earth's magnetic force I effect
in the following manner:-I use two sets of magnets, one set placed fore-and-aft
for counteracting the fore-and-aft component of the ship's magnetism, and the other
set thwartship for counteracting the thwartship component. The thwartship set of
magnets consists of a number of magnetized steel rods of which the true north poles
are preferably coloured blue, and the true south poles red. A vertical row of holes
bored horizontally athwartship in the binnacle or in any convenient solid support
under the compass constitute receptacles for holding the magnets. A sufficient
number of inagnets are placed in these holes to counteract the thwartship component
of the ship's magnetism. The fore-and-aft magnets are similiar to the thwartship
inagnets, and are placed in holes similarly bored fore-and-aft, but I use two vertical
rows fore-and-aft, one on each side of the compass, or one row as nearly under the
centre of the compass card as the tube for the heeling corrector allows in order

page_text: that there may be no perceptible difference in their effect on the compass when the
ship rolls or heels to one side or the other. The holes both for the reception of the
thwartship and fore-and-aft magnets are preferably bored at such distances from
the needles of the compass card that the increase or diminution of the correcting
force on the compass needles caused by raising or lowering a magnet from one hole
to the next one inay be the same, at different levels. The magnets are kept in
position by a door or cover in the shape of a long bar shut across their ends and
secured by lock and key.
My new binnacle, besides the fittings described above for the fore-and-aft and
thwartship magnets, contains as did the binnacles described in the Specifications of
my former Patents, Nos. 1339 and 4876, A.D. 1876, a central tube for heeling
corrector and brackets for carrying quadrantal correctors. The altered plan of
fore-and-aft and thwartship correctors necessitates an altered plan for adjusting and
securing in adjusted position the heeling corrector. In my new binnacle this
corrector consists of oue, two, or three bar magnets in a brass case hung in the
central tube by a chain which passes first horizontally and then vertically down-
wards in the groove in the side of the binnacle adjacent to the outer ends of the
receptacles of one set of the fore-and-aft magnets. This chain is held by a link
thereof being pressed between two pins or the prongs of a fork where it is held
without possibility of dislodgement by the locked bar or door covering the ends of
the said receptacles.
For correcting the part of the fore-and-aft component of the ship's magnetism
which is due to inagnetism induced by the vertical component of the earth's mag-
netic force I have a receptacle fitted to the binnacle in which.a bar of soft iron can
be placed. This bar has the subsidiary advantage of partially or wholly correcting
the residue of the heeling error.
For ascertaining the heeling error I use an auxiliary instrument for comparing
the vertical component of the earth's magnetic force on shore with the vertical
component on board ship. The said instrument is constructed as follows:-Two
magnetic needles of hardened steel wire are joined together and supported on two
iridium points in a line at right angles to the lengths of the needles and passing as
nearly as may be through the centre of gravity of the needles and frame. One of
these points rests on a flat support of sapphire or other suitable hard material, and
the other point rests in or on a cylindrically shaped support of similar hard
imaterial.
The said needles are accurately balanced so as to be horizontal when resting on
the said points before being magnetized, and they are then magnetized. The needles
are brought to a level position again by a vertical magnet placed at equal distances
from the four poles of the needles, and capable of being moved up and down. The
position of the vertical magnet, according as it is higher or lower, gives a greater or
less vertical force on the needles, the amounts of this force being determined by
experiment for different positions of the said vertical magnet.
The improvement in my compass card is for the purpose of preventing the ends
of the needles from catching the silk spokes when the card is thrown up by concus-
sion while guns are being fired. I accomplish this by connecting the ends of the
needles with a silk cord passing through holes drilled in their ends.
And in order that my said Invention may be properly understood, I now proceed
more particularly to set forth the system, mode, or manner in or under which the
same is or may be used or practically carried into effect, reference being had to the
accompanying Drawings and to the letters and figures marked thereon, that is
to say,-
Figures 1, 2, 3, 4, 5, and 6 illustrate an arrangement according to my Invention
for giving steadiness of the compass card without the use of india-rubber bands in
steamers when there is great vibration, Figure 1 representing a vertical section of
the upper part of the binnacle, and of the bowl and its adjuncts, Figure 2 being a
plan of the same, and Figures 3, 4, 5, and 6 being details drawn to an enlarged
scale for the better illustration of certain of the parts.

page_text: According to the arrangement illustrated in the said Figures I hang a gimbal
ring from an elastic metal ring A of an elliptical figure to give different diameters,
one for the supports of the ring upon the binnacle, and the other for the supports
of the gimbal ring. The said ring A is preferably constructed as follows:-A single
brass wire is first bent, and its ends are united by soldering or brazing so as to
form a ring of the proper size. This serves as a core on which a second brass wire
is laid spirally, six turns or thereabouts, round the core, as seen more clearly in
Figure 6. The ends of this second wire are also united by soldering or brazing,
and thus an elastic ring is produced strong enough to support the compass bowl
and gimbal ring, marked respectively B and C. The ring A has two sockets a (see
Figures-3-and 4) fixed at the ends of -its- longer diameter, which sockets Test on
two balls & upon brackets attached to the rim D of the binnacle, or the balls & may
be on the ring and the sockets on the binnacle. Screws a¹ secure the sockets to
the balls so as to allow them to have the requisite motion. This arrangement
mitigates the effect on the knife edges bearing the gimbal ring and bowl and on
the point bearing the compass card of vertical tremors of the platform on which the
compass rests. The knife edges c of the gimbal ring C are supported on two grooved
stirrups e hung by chains e and saddle pieces e¹ on the elastic ring at the ends of
its shorter diameter, as shewn in the details, Figures 5 and 6. The pieces carrying
the knife edges of the gimbal ring are set sufficiently near the outer edge of the
ring to prevent the chains e³ from interfering with the movements of the compass
bowl. The foregoing arrangement mitigates the effect of horizontal tremors of the
platform.
In place of supporting the compass bowl upon a rigid gimbal ring the said rigid
ring may be dispensed with, and the elastic ring A be employed for directly sup-
porting the compass bowl. In this case stirrups are suspended from saddle pieces
by means of chains, as described with reference to the parts e, e', e², Figures 5 and 6,
these saddle pieces being borne on hooks or half rings fixed on brackets attached to
the inside of the fixed upper rim of the binnacle near its upper lip and knife
edges fixed on the underside of the elastic ring A, and at the respective ends of a
diameter thereof rest in the said stirrups. The compass bowl is supported upon the
elastic gimbal ring in a manner similar to that in which the said bowl is supported
upon the rigid gimbal ring C in the arrangement shewn in Figures 1 and 2, the
knife edges of the bowl being supported upon V grooves in plates attached to the
upper side of the elastic ring A at the ends of a diameter at right angles to that
diameter at the ends of which the said ring is suspended from the rim of the
binnacle.
The semicircular error in my improved compasses is corrected by steel magnets,
in accordance with the general principle first given by the Astronomer Royal. The
varying adjustment of the correction required for variation in the ship's sub-
perinanent magnetism and magnetism induced by the vertical component of the
earth's magnetic force I effect in the manner now to be described, reference being
had to Figures 7, 8, and 9 of the accompanying Drawings, of which Figure 7 is a
front elevation of the binnacle; Figure 8, a vertical section through the centre in a
fore-and-aft line; and Figure 9, a horizontal section on the line 1, 2, Figure 7. As
in my former Patents before mentioned the binnacle is furnished with adjustable
quadrantal correctors Z. In front is a clinometer Y. The cover or cap is
marked x.
For correcting the fore-and-aft component of the ship's magnetism I use magnets
arranged in holes, as at M, Figures 7 and 9, and I also use magnets arranged as
at M', in Figures 8 and 9, for correcting the thwartship component. The thwart-
ship set of magnets consist of a number of magnetised steel rods, the true north
poles being preferably coloured blue, and the true south poles being preferably
coloured red. A row of holes, one above the other (see Figure 8) (at equal or
unequal distances apart, but preferably arranged as hereinafter described) is bored
horizontally athwartship in the binnacle, or in any convenient solid support under
the compass, and these holes constitute receptacles for holding the magnets. A

page_text: sufficient number of magnets is placed in these holes to counteract the thwart-
ship component of the ship's magnetism. The fore-and-aft magnets are similar
to the thwartship magnets, and are placed in holes similarly bored, but I use
two vertical rows fore-and-aft, one on each side of the compass, as seen at
M in Figures 7 and 9; or I may use one row as nearly under the centre
of the compass card as the tube for the heeling corrector allows, in order
that there may be no perceptible difference in their effect on the compass
when the ship rolls or heels to one side or the other. The holes both for the
thwartship and fore-and-aft magnets are preferably bored at such distances from
the needles of the compass card that the increase or diminution of the correcting
force on the compass needles caused by raising or lowering a magnet from one holo
to the next one may be the same at different levels. Each series of holes is marked
with a scale such as that illustrated in Figure 94, which scale corresponds to that
described in the Specification of former Letters Patent granted to me, as of the
18th December 1876, and Numbered 4870, the holes for the magnets M, M', being
at elevations corresponding to divisions of this scale. I use generally not less than
two magnets in each row, and I reverse the lower magnet when with two in the
two lowest holes their force on the compass over-compensates the error if they are
turned so as both to pull in the same direction, and if the error is then under com-
pensated I raise the upper magnet until the compensation is obtained. The magnets
are kept in their places by doors or covers f secured by lock and key.
For correcting the part of a fore-and-aft component of a ship's magnetism which
is due to magnetism induced by the vertical component of the earth's magnetic
force I have a receptacle G, shewn in Figures 8 and 9, fitted to the binnacle, in
which receptacle a bar of soft iron H can be placed. As it can only be found by
observation on board the ship in different magnetic latitudes to what height this
bar must be raised and how large it must be there may be provided on board bars
of different length for placing in the receptacle G. For raising the bar to a greater
or less elevation there are provided a number of pieces of wood, as at g in Figure 8;
and by placing a greater or less number of these pieces beneath the bar H, the said
bar may be supported in a higher or lower position. Pieces of soft iron corre-
sponding to the pieces of wood may also be provided, so that by substituting the
said pieces of iron for one or more of the pieces of wood the effective length of the
bar may be increased or diminished as desired. By this arrangement of dividing
the lower part of the bar into several pieces and the use of pieces of wood I avoid
the necessity of providing several lengths for adjusting the degree of correcting to
what observation at sea shews to be required. The receptacle G may have a door
at its lower part, as at g³, to retain the loose pieces, whether of wood or iron, in
position. The upper end of the bar H is preferably somewhat above the level of
the needles, as shewn in the Drawings, so that the said bar may partially or wholly
correct that part of the heeling error which depends on the variation in the ship's
magnetism produced by differences in the vertical component of terrestrial magnetic
force in different localities.
The instrument for comparing the vertical force on shore with the vertical force
en board ship is shown in Figures 10, 11, 12, 13, 14, and 15, Figures 10 and 11
being respectively side and end elevations of the said instrument; and Figure 12
being a side elevation with the casing and certain other parts in section; and
Figures 13 and 14 transverse sections taken respectively on the lines 3, 4, and 5, 6,
Figure 12; Figure 15 is a plan, partly in section, of the said instrument. i, i, are
magnetic needles formed of hardened steel wires or bars, connected together by the
framework j and supported on the tops of the two columns by two iridium points k
in a line at right angles to the length of the wires, and passing as nearly as may be
through or a little above the centre of gravity of the two needles and their frame.
One of these points rests on a plane surface at the top of one of the columns (see
Figure 13), and the other on a cylindrical surface m at the top of the other of the
columns, the axis of the cylinder being parallel to the needles. Each of these
surfaces is of a hard substance, such as sapphire or glass. Guards are attached to

page_text: the tops of the columns projecting above the hard bearing surfaces l, m, as seen in
Figure 13, by which the arms carried by the iridium points are prevented from too
great motion in any horizontal direction, particularly directions parallel to the
needles. The needles i, i, and their frame are accurately balanced so as to be hori-
zontal when resting on the points and m before being magnetized, and they are
then magnetized. Horizontal lines, preferably black on white ground, are ruled on
the sides of the containing case to shew horizontality of the needles. A vertical
magnet n is inserted in the hollow rod p, which is so situated that the said
magnet n is at equal distances from the four poles of the magnets i, i. The said
rod p is screwed on its exterior and works in a nut q, which is so connected to the
top of the box of the instrument that it has no_vertical_movement, and so that
by turning the said nut q the rod p and magnet n can be raised or lowered,
and the force on the needles i, i, adjusted so as to counteract the vertical
magnetic force at any particular place. One side of the rod p is flattened
or grooved, and its lower end runs in a guide 7, with a filling pieco therein
corresponding to the flattened part or groove, so that the said rod p cannot
rotate. A scale of divisions corresponding to the threads of the screw is
engraved on the flat or groove by which the elevation of the magnet n carried
thereby may be ascertained, and the indications of this scale are subdivided by
dividing the rim of the nut q into divisions to indicate portions of a rotation.
When the instrument is being carried about the magnets i are supported on the
platform 8, which platform can be raised by means of the eccentric t, which is upon
a stem t¹ projecting to outside the casing where it has a handle t. The said
eccentric engaging in a slot in a depending piece s¹ upon which the platform & is
mounted, the said piece & sliding in sletted guides in the sides of the casing of the
instrument, as seen in Figure 15. The instrument is furnished with a spirit
level u, and has a glass top to its casing. When the instrument is used in the
binnacle the compass bowl is taken out, and the said instrument is supported from
the brass rim of the binnacle (as shewn in Figure 8) by means of four hooks vat
the ends of two cords v passing through the holes in the casing of the said
instrument. One end of each cord v¹ is fixed to a tent rope-bead v³, as shewn in
Figures 10 and 11. By means of the tent rope beads the lengths of the cords v
may be altered to adjust the instrument at a level (which may be ascertained by
the spirit level u) and to the proper height. To.correct the heeling error by this
instrument it is first taken on shore and the vertical magnet n is raised.or lowered
until the magnets i, i, are horizontal when the reading of the scale on the rod p is
noted. The nut q is then turned so as to diminish the effect of the magnet n on
the magnets i, i, to the proper theoretical proportion called in the Admiralty
Compass Manual. The instrument is then taken on board the ship and placed in
the binnacle in the manner before described, and the vertical magnet (marked w in
Figure 8) in the binnacle is then raised or lowered by its chain w until the needles
rest balanced in their horizontal sighted position. The chain of the said magnet w
is then secured so as to retain the said magnet in the position to which it has been
brought by passing a link thereof between a fork or its equivalent, situated at the
position marked W in Figures 7 and 9. The said fork is shown separately to a
large scale in Figure 7 where it is marked W, a part of the chain w¹ of the magnet
being also shewn. The doors when closed will cover this fork W and the end of
the chain w' and secure the said chain.
In Figures 1 and 2 I have shewn my improvement in the compass card for pre-
venting the ends of the needles a from catching in the silk cordis constituting tho
spokes y of the card if the said card is thrown up. The said improvement consists
in connecting the ends of the said needles a by a silk cord or cords passed through
holes drilled in their ends, as will be readily seen by reference to the said Figure 2,
where the cord or cords are marked z. The said cords will prevent the ends of the
needles from catching over the cords y.
Having now described and particularly ascertained the nature of my said Inven-
tion, and the system, mode, or manner in or under which the same is or may be

page_text: used or practically carried into effect, I would observe in conclusion that what I
consider to be novel and original and therefore claim as the Invention secured to
me by the hereinbefore in part recited Letters Patent is,-
First. Supporting the bowl of mariners' compasses by means of an elastic ring,
whether with the intervention of a rigid gimbal ring or not, essentially as herein-
before described and illustrated in Figures 1, 2, 3, 4, 5, and 6 of the accompanying
Drawings. Also the herein before described construction of the said elastic ring.
Second. In cases where a rigid gimbal ring is employed the mounting of the
elastic ring referred to in the preceding claiming clause upon the balls and sockets
(a, d,) and the hanging of the rigid gimbal ring from the said elastic ring (or in
cases where the elastic ring is used as a gimbal ring then the hanging of the
said elastic ring from fixed hooks) by the stirrups e, chains e², and saddle pieces c',
as hereinbefore described, and illustrated in Figures 1, 3, 4, 5, and 6 of the accom-
panying Drawings.
Third. The arrangement of receptacles for containing the magnets for correcting
the semicircular error of mariners' compasses, as described with reference to
Figures 7, 8, and 9 of the accompanying Drawings.
Fourth. The graduation of the positions of the receptacles referred to in the last
preceding claiming clause, and the numbering of them according to a scale of
degrees of correcting force produced by the magnets on the compass, as herein-
before described.
Fifth. The bars or doors f fastened across the ends of the correcting magnets
to secure them in their adjusted positions until re-adjustment is to be performed.
Sixth. Combining with the binnacle a bar of soft iron (H), also the receptaclo
for holding the same and the pieces of wood and iron at the lower part thereof, as
and for the purpose specified.
Seventh. The auxiliary instrument for ascertaining the heeling error in mariners'
compasses, the said instrument being constructed essentially as horcinbefore
described, and illustrated in Figures 10 to 15 of the accompanying Drawings.
Eighth. The means for preventing the needles (a) from catching into the silk
cords (y) constituting the spokes of the cards of mariners' compasses consisting of
the cord or cords attached to the ends of the said needles, as herein before
described with reference to Figures 1 and 2 of the accompanying Drawings.
In witness whereof, I, the said Sir William Thomson, have hereunto set my hand
and seal, this Eighth day of August, in the year of our Lord One thousand
eight hundred and seventy nine.
WILLIAM THOMSON. (L.S.)