IMPROVEMENTS IN INSTRUMENTS OR APPARATUS FOR FINDING THE TRUE OR MAGNETIC MERIDIAN
Year: 1878

page_text: LETTERS PATENT to James Morton, of Sunderland and South Shields, in the
County of Durham, Compass and Chronometer Maker, for the Invention of
"IMPROVEMENTS IN INSTRUMENTS OR APPARATUS FOR FINDING THE TRUE
OR MAGNETIC MERIDIAN."
Sealed the 5th November 1878, and dated the 24th May 1878.
PROVISIONAL SPECIFICATION left by the said James Morton at the Office
of the Commissioners of Patents on the 24th May 1878.
JAMES MORTON, of Sunderland and South Shields, in the County of Durham,
Compass and Chronometer Maker. "IMPROVEMENTS IN INSTRUMENTS OR APPARATUS
FOR FINDING THE TRUE OR MAGNETIC MERIDIAN."
This Invention, which relates to improvements in apparatus for finding the true
or inagnetic meridian of any place of observation, by observation of the sun or inoon,
or of a star, or planet, or known celestial body, the latitude of the place of observa-
tion, and the declination and hour angle of the observed body being known, has
especial reference to an improved azimuth circle, and to certain improvements
applicable in the construction of the instrument generally known as the Palinurus
compass correcter or compass error detecter.
The improved azimuth circle is constructed with a horizontal circle or plate
graduated on its upper surface with degrees and points of the compass, and movable
about a central vertical axis supported in a gimbal to keep the plate truly level.
At the centre of this horizontal plate, and capable of being moved independently
thereof about its vertical axis there is a support provided with an index, and
carrying a horizontal axis, which, by the support being turned about it's axis, can
be set at any required angle to the meridian, or north and south diameter of the
horizontal plate, the index being attached to the support for the purpose of reading
that axle on the horizontal circle or plate. Moving about the horizontal axis, and
with its plane parallel to it, there is a graduated time circle, the diameter of which
Dine 871

page_text: at right angles to its axis being its meridian line; this circle by being moved about
its axis, and by means of a graduated semicircle attached to its under side, may be
set at any required angle to the horizontal circle.
At the centre of the time circle, and perpendicular to its plane, there is an axis
or socket movable, about which there is a telescope, or sight, or shadow piece
having a line of collimation made by cross hairs, threads, or wires, or otherwise, and
which line of collimation may be adjusted at any required angle to the plane of the
time circle. This telescope or sight, with its means of adjustment, at an angle to
the plane of the time circle, may be constructed in various ways, as hereafter
described, but I prefer the arrangement I now proceed to describe.
Movable about the perpendicular axis, at the centre of the time circle, there is a
support provided with an index, and carrying parallel to the time circle, an axis
moveable about, which, and at right angles to it there is a bar of convenient length
which carries at each extremity, and placed at right angles to its length, a sight
vane, the one next the eye having a small aperture and the other a large aperture,
across which are stretched two cross wires, hairs, or threads at right angles to each
other, the centre of the small aperture in the one vane and the point of intersection
of the cross wires in the other are in the line of collimation, which, by means of an
index attached to the bar moving on a graduated declination are carried by its
support, may be inclined at any required angle to the plane of the time circle, as
above mentioned, and by the index attached to the support may be read on the
time circle; the angle which the line of collimation makes with the plane perpen-
dicular to the time circle, and in which its meridian line is; or, in lieu of this
arrangement, when required for observing stars of (say) less than the second
magnitude a telescope like that used with a sextant may be mounted in a similar
way to the two sight vanos; or I adapt about the perpendicular axis at the centre
of the time circle a moveable arm, either or both of the sight vanes being made
to slide on branches thereof, in a plane perpendicular to the time circle, there
being a scale attached to or carried by one branch, on which may be read the
angle which the line of collimation makes with the plane of the time circle, and an
index being attached to the arm for reading on the time circle, the angle made by
the line of collimation with its meridian. Or I adapt, about the perpendicular axis
at the centre of the time circle, a moveable arm with an attached index, as in the
preceding modification, and provided also with a point formed by the intersection
of cross threads or otherwise, and from which degrees are projected on to another
part of the arm, and in a plane perpendicular to the time circle, so as to form a
graduated line in the arm; then the shadow of the cross threads at their inter-
section (or of the point as otherwise formed) as cast by the sun or moon in
falling upon the graduated line measures the angle which the observed body makes
with the plane of the time circle.
Now, in order to find the true meridian by the above-described improved
instrument, the axis of the time circle is set at right angles to the meridian, or
north and south diameter of the horizontal circle, and the time circle is adjusted
on its axis at an angle to the horizontal circle, equal to the co-latitude of the place
of observation; the line of collimation of the sight is also set at an angle to the
plane perpendicular to the time circle, and in which its meridian line is equal
to the hour angle of the observed body, and at an angle to the plane of the
time circle, equal to its declination. The horizontal circle is then turned on its axis
until on looking through the small aperture in the sight vane, the object appears
at the intersection of the cross threads in the other sight vane; or if the sun or
noon be observed, and the light strong enough to cast a visible shadow, until the
shadow of the one sight vane falls upon the other, or more exactly until the shadow
of the cross threads at their intersection falls upon the small aperture of the other
or opposite sight vane; then the north and south points of the horizontal circle
will be in and will indicate the true meridian.
If the magnetic meridian be required the manipulation of the apparatus is the

page_text: same as just described, except that instead of setting the axis of the time circle
at right angles to the meridian or north and south diameter of the horizontal circle
it must be set to it at an angle differing from a right angle by the variation of the
magnetic needle at the place and time of observation.
With reference to the instrument known as the Palinurus compass correcter, or
compass error detecter, my improvements consist in adapting to it a means of
observing any of the colestial bodies at their angle of declination from the plane of
the equator.
By constructing the telescope sight or shadow piece (which is movable about
the perpendicular axis or socket at the centre of the time circle of the instrument),
so that it may have a line of collimation or observation, which may be adjusted
to the plane of the time circle (which represents the plane of the equator) at an
angle equal to that which the observed body makes with the plane of the equator;
or by constructing the shadow piece so that it may indicate the angle at which a
shadow, as cast by the observed body, is projected to the plane of the time circle;
and by fitting to the telescope sight or shadow piece a mirror or reflector for the
purpose of seeing the object by reflection when a direct view cannot be conveniently
obtained.
The advantages gained by these improvements are that in low latitudes an exact
observation may be obtained by observing any of the celestial bodies visible not too
near the vertex which, with the instrument as hitherto constructed, is impossible.
And that in low latitudes (or even in latitudes as high as 60 degrees, when the
object has a large hour angle) a good observation may be made when the declina-
tion of the observed body and the latitude of the place of observation only are
known. Also, that if any considerable error has been made in computing the hour
angle of the body observed, the instrument will in most cases show it, and in low
latitudes always.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said James Morton in the Great Seal Patent Office on the 23rd November
1878.
JAMES MORTON, of Sunderland and South Shields, in the County of Durham,
Compass and Chronometer Maker. "IMPROVEMENTS IN INSTRUMENTS OR APPARATUS
FOR FINDING THE TRUE OR MAGNETIC MERIDIAN."
This Invention, which relates to improvements in apparatus for finding the true
or magnetic meridian of any place of observation by observation of the sun, or
moon, or of a star, or planet, the latitude of the place of observation and the
declination and hour angle of the observed body being known, the variation of the
magnetic needle at the time and place of observation being also known, in finding
the magnetic meridian, has especial reference to an improved azimuth circle or
altazimuth compass corrector, and to certain improvements applicable to the instru-
ment generally known as the "Palinurus," "compass corrector," or
detecter."
compass error
The improved azimuth circle, which is illustrated on Sheet 1 of the accompanying,
four Sheets of Drawings in elevation in Figure 1, the upper half of its box or case 1
being removed, and the lower half shown in section in order to illustrate more
clearly the manner in which the instrument is suspended therein is constructed
with a horizontal circle or plate 2 (see the sectional detail view, Figure 2, Sheet 2),
which is graduated on its upper surface with degrees and points of the compass,
as shown in Figure 3, Sheet 3, and is secured to a tube 3 (Figure 2) in such a
manner as to be movable about its axis, the tube 3 working within the boss 4 of
an encircling ring 5, connected thereto by radiating arms 6, and supported at
opposite points 7 (Figure 1) in a ring 8 which is supported at opposite points 9 at
right angles to those 7 in standards or bearings 10, scrowed or secured to the sides
of the case or box 1, so that the plate 2 shall be suspended in a horizontal plane by
means of a weight 34.
At the centre of the plate 2 is a vertical support 11 (see Figure 1) provided with
an index 12, and carrying or being intended to support a horizontal axis 13, which
can be set at any required angle to the meridian or north and south diameter of
the plate 2, the index 12 being attached to the support 11 for the purpose of
setting the same and reading the angle on the plate 2, as shown in Figure 3, the
support 11 being capable of being moved about its axis, and that of the plate 2,
independently of the latter, being provided with an axis 14, which works within
the tube 3, and is secured by a screw 15 in the manner shown in Figure 2.
Movable about the axis 13, and with its plane parallel to it, there is a time
circle 16, graduated as shown in Figure 4, Sheet 3, its diameter at right angles to
its axis 13 being its meridian line; this circle 16 by being moved about its axis 13,
and by means of a semicircle 29, attached to its under side, and graduated with
degrees, as shown in Figure 1, may be set at any required angle to the horizontal
plate 2, as shown in Figure 2, and secured in such position if desired by a set
screw 17 (see Figure 3), the angle being observed and set through the index
aperture 18 in the standard 11.
At the centre of the time circle 16, and perpendicular to its plane, there is an
axis or socket 19 (see Figure 2), which in the manner illustrated in Figures 1
and 4 may support any of the instruments illustrated in Figures 5 to 12, Sheet 4,
which represent various sights or shadow pieces, each of which, so far as regards
the instruments, illustrated in Figures 5 to 10, has a line of collimation made as in
a telescope by cross hairs, threads, or wires, or otherwise, and which may be
adjusted at any required anglo to the plane of the time circle 16 (as shown in
Fig. 5), the instruments being provided with properly projected degrees or gradu-
ated scales on which the same may be read, and being movable about the axis 19
the line of collimation may also be set at any desired hour angle to the plane per-
pendicular to the time circle, and in which its meridian line is, as shown in
1

page_text: Figure 4, an index 20 being attached to each instrument for reading the hour angle
thus made.
These sight or shadow giving instruments may be constructed in various ways to
fulfil these conditions, but I prefer the arrangements I will now describe, especially
those illustrated in Figures 1 and 4 to 8.
In Figures 1 and 4 to 6 the instrument is shown as formed with a support 21,
graduated at 28, as shown in Figures 1 and 5, and provided with an index 20, and
carrying parallel to the time circle 16 an axis 22, movable about which and at right
angles to it there is a bar 23, of convenient length, which carries at each extremity,
and placed at right angles to its length, a sight vane 24, the one nearest the cyc
having a small aperture 25 and the other a larger aperture, across which aro
stretched two cross wires, hairs, or threads 26, at right angles to each other, the
centre of the small aperture in the one vane and the point of intersection of the
cross wires in the other being in or forming the line of collimation, which by means
of an index 27 attached to the bar 23, and moving on the graduated declination
are 28, marked on or carried by the supports 21, may be inclined, as shown in
Figure 5, at any required angle to the plane of the time circle 16, as above
imentioned; and by the index 20; attached to the support 21, may also he set to
auy desired hour angle to the plane perpendicular to the time circle, and in which
its meridian line is, as also above mentioned and as illustrated in Fig. 4.
In the instrument, illustrated in Figures 7 and 8, the declination arc is more
extended than illustrated in Figures 1 and 5, ranging from 90 degrees N. to
90 degrees S., and it is mounted in its support 21 in the same way as the time
circle 16, with its attached semicircle 29 for latitude.
In the instrument illustrated in perspective in Figure 9 the index wire 27-20
is movable, degrees being properly projected from the sight aperture 25 on to a
branch 24 of the bar 23.
In the instrument, illustrated in perspective in Figure 10, the wires or threads 26
are fixed, and the sight aperture 25 (shown in the sectional detail view, Figure 18)
with an attached index line 27, movable, the degrees being properly projected from
the intersection of the cross wires on to the opposite or sight branch 24*; thus,
in either of the instruments illustrated in Figures 9 and 10, the line of collimation
admits of being adjusted at an angle to the plane of the time circle as measured on
the graduated scale, equal to that which the observed body makes with the plane
of the equator.
In the instrument illustrated in Figures 11 and 12, which represent a shadow
piece, the branches 24* are provided, the one with cross hairs or wires 20 and the
other with a scale of degrees properly projected from the intersection thereof, and
having a central slit made in or vertical lino drawn on it. In this case the angle
of declination is measured and ascertained by observing the degree of the scale on
which the shadow of the cross thread falls.
It is obvious that the graduated branches of the instruments, illustrated in
Figures 9 to 12, need not necessarily be perpendicular to the plane of the time
circle, nor is it necessary for them to be straight, they might be curved, as dotted
in Figure 11, or of other forms, and would act just the same, provided the degrees
be correctly projected on them from the sight aperture or point of intersection of
the cross threads, in such a manner that the shadow of the cross threads at their
intersection (or of the point as otherwise formed) as cast by the sun or moon in
falling upon the graduated line measures the angle which the observed body makes
with the plane of the time circle. Now in order to find the true meridian of any
place of observation by observation of (say) the sun, by the above-described improved
instrument, the instrument is manipulated as follows, and to render the descrip-
tion more easily understood, let us suppose that it is required to find the true
meridian in London on the Twenty-sixth day of November, A.D. 1878, at
2 o'clock p.m. apparent time. In this illustration let reference be made to the
perspective diagram, Figure 17, which illustrates the setting of the various parts
for this example:

page_text: The axis 13 of the time circle 16 is first set at right angles to the meridian, or
north and south diameter of the horizontal circle or plate 2, which is effected by
setting its pointer 12 to the north point of the latter. The time circle 16 is then
adjusted on its axis 13, at an angle to the horizontal circle, equal to the co-latitude
of the place of observation, which in the present case is about thirty-eight and a half
degrees, and this is effected by setting the latitude arc 29, so that the index line in the
aperture 18 of its support 11 agrees with the latitude of the place, in this case about
fifty-one and a half degrees North. The sighting piece is then placed in position on
the perpendicular support 19 of the time circle 16, and its line of collimation or
sight is set at an angle to the plane perpendicular to the time circle, and in which
its meridian line is equal to the hour angle of the observed body, which in this case
is two o'clock p.in., and this is effected by setting the index 20 of the sighting piece
to 2 p.m., using the outer circle of figures on the time circle, and by setting its line of
collimation also at an angle to the plane of the time circle equal to the declination of
the observed body; and this is effected by adjusting the pointer 27, marked "For 1
N. Latitude" (there being two pointers 27 in the instruments illustrated in Figures 5
to 8, one of which is marked "For N. Latitude," and the other of which is marked
"For S. Latitude") on the declination arc 28, to the sun's declination, say about
twenty-one degrees South.
All these adjustinents being correctly made, the horizontal circle is then turned
on its axis 3 by means of its knobs (30) until the shadow of the one sight vane
falls upon the other; or, more exactly, until the shadow of the intersection of the
cross threads or wires 20 falls upon the small aperture 25 in the opposite sight
vane, or until on looking through the small aperture in the one sight vane, the
sun appears at the intersection of the cross wires in the other. Then the north and
south points of the horizontal circle will be in and will indicate the true meridian.
If the imagnetic meridian be required, the manipulation of the apparatus is the
same as above described, except that instead of setting the axis 13 of the time
circle at right angles to the meridian, or north and south diameter of the horizontal
circle 2, it must be set to it at angles differing from right angles by the variation 3
of the magnetic needle at the time and placo of observation.
In using the instrument on board ship, it is placed directly in the fore-and-aft
line of the ship, the clinometer 31 (see Figure 1) registering 0° (on a graduated
scale 32), when the ship is upright, and the index 12 on the compass dial 2, set to
the proper variation, and the latitude are 29 being set to correspond on its index 3
line 18 to the ship's position in latitude, the proper adjustment is then made to
declination, using the pointer 27 marked for the proper latitude, and the index 20
is set on the time circle 16 to the apparent time or hour angle. Then on turning
round the compass dial by its two knobs until the observed object is in line with
the line of collimation as above described, the fore-and-aft diameter of the compass
dial will show the magnetic direction of the ship's head. When from the position
of the instrument a direct view cannot be got, attach the mirror illustrated in
Figure 16 to the arm of the sight vane, as dotted in Figure 5, to reflect the image
of the object to the eye.
If after making the above adjustments it is found on revolving the dial that the
object has not the same altitude as the sight vanes, but appears considerably above
or below the intersection of the cross threads, it shows that some error has been
made in allowing for either latitude, declination, or time, this is a very useful
check, and makes an erroneous observation almost impossible. If, however, the
object appears with a degree above or below the centre of the sight vane, probably
the adjustments are correct, as a little difference may be caused by refraction and
parallax, and by the dial from the motion of the ship not having an exactly level
position in its gimbal at the moment of observation."
The hour angle may be found by the instrument after adjustment to latitude and
declination by moving the index on time circle (observing that it is on the same E
side of the meridian as the object), till ou moving round the dial the object appears
at the intersection of the cross threads. This is a very easy method of observation,

page_text: the latitude and declination only being required; it should not be used however in
latitude exceeding 60°, nor when the object is less than two or three hours from the
meridian.
With reference to the instrument known as the Palinurus compass corrector, or
compass error detecter, which as hitherto constructed is defective in principle, not
having any adjustment to declination, in consequence of which no reliable observa-
tion can be made by it in low latitudes; my improvements consist in constructing
the sight or shadow piece (which is movable about the axis or socket (19) at tho
centre of the time circle (16) of the instrument) in any of the ways above described,
and illustrated in Figures 5 to 10, having a line of collimation or observation
which admits of being adjusted to the plane of the time circle at an angle equal to
that which the observed body makes with the plane of the equator, or by con-
structing the shadow piece, as illustrated in Figures 11 and 12, so that it may
indicate the angle at which a shadow as cast by the observed body is projected to
the plane of the time circle, in lieu of forming it as hitherto, without such means of
indication, as illustrated in Figures 13 to 15, and by fitting to the sight or shadow
piece, a reflector or mirror 33, illustrated in Figure 16, and in position in dotted lines
in Figure 5, for the purpose of seeing the object by reflection, when a direct view
cannot be conveniently obtained.
The advantages gained by these improvements are, that the above defect is re-
moved, and that in low latitudes an exact observation may be obtained by observing
any of the celestial bodies visible, not too near the vertex, which with the instrument
as hitherto constructed is impossible. And that in low latitudes (or even in latitudes
as high as sixty degrees, when the object has a large hour angle), a good observation
may be made when the declination of the observed body and the latitude of the
place of observation only are known, thus requiring no calculation. Also, that if
any considerable error has been made in computing the hour angle of the body
observed, the instrument will in most cases show it, and in low latitudes always
because when all the adjustments of the instrument are correctly made (as above
described), the line of collimation of the sight vanes takes the same altitude or
angle of elevation as the body under observation, and on the horizontal circle being
turned to its proper position, will point exactly to it, whereas, if the adjustment to
time or hour angle has been incorrectly made, the line of the sight will point either
too high or too low, and this is much more noticeable near the equator when the
altitude of a celestial body changes more rapidly than it does when the observer is
farther from it. Thus, by the above-described altazimuth compass corrector, or by
the usual Palinurus, as adapted with my above-described improvements, the navi-
gator may in any part of the world, ascertain with certainty the deviation of his
compass by observation of the sun, moon, or of a star, or planet, all required being
a knowledge of his position in latitude, together with the apparent time or hour
angle of the body observed and its declination, or the other data above mentioned.
Having now described the nature and object of my said Invention, together with
the manner in which the same is to be or may be performed or carried into practical
effect, I would remark in conclusion that I claim as my Invention,-
The construction of apparatus for finding the true or magnetic meridian of any
place of observation, by observation of the sun, moon, or of a star, or planet, the
latitude of the place of observation, and the declination and hour angle of the
observed body being known, the variation of the magnetic needle at the time and
place of observation being also known, in finding the magnetic meridian, substan-
tially as above described, and as illustrated on the accompanying Drawings.
Also the adaptation to the instrument known as the Palinurus compass corrector,
or compass error detector, of sight or shadow pieces constructed in such a manner
as to have a line of collimation or observation which admits of being adjusted to
the plane of the time circle at an angle equal to that which the observed body
makes with the plane of the equator, or in such a manner as that they may indicate
the angle at which a shadow as cast by the observed body is projected to the plane
of the time circle of the instrument (in lieu of forming them as hitherto, without

page_text: such means of indication), and the fitting to the sight or shadow pieces of a reflector
or mirror, for the purpose of seeing the object by reflection when a direct view
cannot be conveniently obtained, substantially as above described, and as illustrated
on the accompanying Drawings.
In witness whereof, I, the said James Morton, have hereunto set my hand
and seal, this Twentieth day of November, in the year of our Lord One
thousand eight hundred and seventy-eight.