IMPROVEMENTS IN THE METHOD OF AND APPARATUS FOR ASCERTAINING LATITUDE, LONGITUDE
Year: 1866

page_text: LETTERS PATENT to John Martin Rowan, of Glasgow, in the County
of Lanark, North Britain, and Alexander Morton, of Kilmarnock, in
the County of Ayr, North Britain, for the Invention of "IMPROVEMENTS
IN THE METHOD OF AND APPARATUS FOR ASCERTAINING LATITUDE, LONGITUDE,
Sealed the 28th September 1866, and dated the 3rd April 1866.
PROVISIONAL SPECIFICATION left by the said John Martin Rowan
and Alexander Morton at the Office of the Commissioners of Patents,
with their Petition, on the 3rd April 1866.
We, JOHN MARTIN ROWAN, of Glasgow, in the County of Lanark, North
Britain, and ALEXANDER MORTON, of Kilmarnock, in the County of Ayr,
North Britain, do hereby declare the nature of the said Invention for "IMPROVE,
MENTS IN THE METHOD OF AND APPARATUS FOR ASCERTAINING LATITUDE, LONGITUDE,
AND GREENWICH TIME," to be as follows, that is to say :-
This Invention has for its object to facilitate the ascertaining of latitude,
longitude, and Greenwich' time, and its application is not limited like other
plans to mid-day observations, but is equally available with observations
taken of the sun, moon, or stars at any hour of the twenty-four.

page_text: The improved method is based upon the principle that when the sun, moon, or
a star shows a certain angle of altitude to an observer it will be in the zenith
of a point on the earth's surface, the angular distance of which from the
observer is equal to the complement of the angle of altitude, that is, to the
difference between that angle and a right angle; and if a circle is described
on a sphere with its axis passing through a point corresponding to the zenith
point, and its circumference passing through a point corresponding to the
observer's station, the sun, moon, or star will show the same altitude to all
points in that circle. The observation thus serves to define a circle at some
part of which the observer's station must be, and the problem is reduced to
that of finding the required point on this circle, the manner of accomplishing
which will be most easily understood from the following description of the
improved apparatus and method of using it.
In one modification of the apparatus there is an equatorial ring having
degrees of longitude marked upon it, and which is fixed on a polar spindle.
On this spindle there are fitted two half rings or ares marked with degrees of
latitude, and made capable of adjustment separately, being both at right angles
to the equatorial ring, and of a radius to work just outside of that ring.
*Pinching screw clamps are provided for fixing the latitude arcs in any positions
on the equatorial ring, and verniers are adapted to all three scales of degrees
-to facilitate accurate adjustment. The verniers on the latitude arcs have
small holes for receiving the points of a loose angular distance segment. This
is a segment of a little larger radius than the latitude arcs, and it is marked
with degrees and is fitted with a vernier formed with a projecting pin, whilst
another pin is fixed to the segment itself at the zero or 90-degree point. This
segment is used after the manner of a pair of drawing compasses.
To ascertain longitude from a solar observation, latitude being known, Green-
wich time at the instant of observation is noted by the chronometer; one of
the latitude arcs is clamped on the equatorial ring to correspond to that time,
and the vernier on this arc is set to the sun's declination as given in the
Nautical Almanack for that day. The vernier on the other latitude arc is set
to the latitude and clamped, and the loose segment is set and clamped to the
complement of the angle of altitude as ascertained by the observation. One
pin of the loose segment is then placed in the vernier hole of the latitude arc
already clamped, and the other latitude arc is adjusted until the other pin of
the segment enters its vernier hole; then this latitude arc will mark the
longitude required on the equatorial ring. If the longitude is known and the
latitude is sought the same adjustments are made, excepting that the second
latitude arc is clamped in the said longitude position, and its vernier is

page_text: adjusted until the segment pin enters its hole, when the vernier will mark the
latitude.
If the latitude and longitude are known and Greenwich time is sought,
one latitude arc is set to the longitude and clamped upon the equatorial
ring, and the vernier on it is set and clamped to the latitude; the other
latitude arc has its vernier set to the sun's declination and clamped, and the
segment is then set to the complement of the angle of altitude, and one of its
pins is set in the vernier of the fixed latitude arc, whilst the other latitude
arc is adjusted until the other segment pin enters its vernier hole, whereupon
this arc will mark Greenwich time upon the equatorial ring.
In order to ascertain latitude and longitude, both being unknown, two observa-
tions are required to be taken, either simultaneously of two heavenly bodies or
at a known interval of time of the sun. The apparatus must also be provided
with a third latitude arc with its vernier and clamp, and the segment must have
two limbs hinged together, and each with a vernier and pin; with a third pin
in the axis of the hinge joint. When using two solar observations the verniers
of two of the latitude arcs are set and clamped to the sun's declination, and
the arcs are set, and clamped on the equatorial ring to the Greenwich times
of the two observations respectively. The two verniers of the hinged segments
are set and clamped to the respective complements of the angles of altitude of
the observations. The hinged segment is then set with its two vernier pins
in the vernier holes of the fixed latitude arcs, and its hinge pin will then
coincide in position with the observer's station; and when the third latitude
arc and its vernier are set to it the vernier will mark the latitude, and the arc
itself will mark the longitude on the equatorial ring. With simultaneous
observations of two heavenly bodies the two latitude arcs are set and clamped
at the respective right ascensions on the equatorial ring, and their verniers are
set and clamped, at their respective declinations. The hinged segment is then
applied in the same way as with the two solar observations.
It will be obvious that the details of construction of the apparatus may be
varied, thus the latitude arcs, or some of them, may be either within or without
the equatorial. ring; and if the space within is occupied with a terrestrial
globe it will facilitate the adjustment of the ares, and will enable the user to
realise the signification of the operations he has to perform.

page_text: by the said John Martin Rowan and Alexander Morton in the Great
Seal Patent Office on the 3rd October 1866.
TO ALL TO WHOM THESE PRESENTS SHALL COME, we, JOHN
MARTIN ROWAN, of Glasgow, in the County of Lanark, North Britain, and
ALEXANDER MORTON, of Kilmarnock, in the County of Ayr, North Britain,
send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Third day of April, 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 uuto
us, the said John Martin Rowan and Alexander Morton, Her special
licence that we, the said John Martin Rowan and Alexander Morton;
our executors, administrators, and assigns, or such others as we, the said
John Martin Rowan and Alexander Morton, our 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
Kingdom of Great Britain and Ireland, the Channel Islands, and Isle of
Man, an Invention for "IMPROVEMENTS IN THE METHOD OF AND APPARATUS
FOR ASCERTAINING LATITUDE, LONGITUDE, AND GREENWICH TIME," upon the
condition (amongst others) that we, the said John Martin Rowan and
Alexander Morton, our executors or administrators, by an instrument in writing
under our, 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.
1..
NOW KNOW YE, that we, the said John Martin Rowan and Alexander
Morton, do hereby declare the nature of our said Invention, and in what
manner the same is to be performed, to be particularly. described and
ascertained in and by the following statement in writing, reference being had
to the accompanying Drawings, that is to say :-
Our said Invention has for its object to facilitate the ascertaining of
latitude, longitude, and Greenwich time, and its application is not limited

page_text: like that of ordinary plans to mid-day observations, but is equally available
with observations taken of the sun, moon, or stars at any hour of the twenty-
four.
Our improved method is based upon the principle that when the sun, moon,
or a star shows a certain angle of altitude to the observer it will be in the
zenith of a point on the earth's surface, the angular distance of which from
the observer is equal to the complement of the angle of altitude observed,
that is, to the difference between that angle and a right angle; and if a circle is
described on a sphere with its axis passing through a point corresponding to
the zenith point, and its circumference passing through a point corresponding
to the observer's station, the sun, moon, or star will show the same altitude to
all points in that circle. The observation thus serves to define a circle on the
earth's surface, at some part of which circle the observer's station must be,
and the problem is reduced to that of finding the required point on this
circle, the manner of accomplishing which will be most easily understood
from the following description of the improved apparatus and method of
using it.
A modification of our improved apparatus is represented upon the
accompanying Sheet of explanatory Drawings, Figure 1 being a plan, and
Figure 2 a partially sectioned elevation. In this modification there is a com-
plete equatorial ring E having degrees of longitude marked upon it, and which
is fixed on a polar spindle P, having its ends resting in bearings in a standard
frame F. When making use of the instrument the equatorial ring E is
turned so as to bring uppermost the part corresponding to the hemisphere of
the earth in which the observation is made, and it is fixed in that position by
a screw clamp fitted upon the middle of the sole of the standard frame F.
On the polar spindle P there are fitted two half rings or arcs D, L, marked
with degrees of latitude and. made capable of adjustment separately on the
spindle P, as upon hinges, being both set with their planes at right angles to
the equatorial plane and ring E, and having a radius to work just outside of
that ring. Pinching screw clamps t, e, are provided for fixing the arcs D, L,
in any positions on the equatorial ring E, and similar clamps d, l, are.
provided on the ares, all the four clamps being marked with vernier
scales to facilitate accurate adjustment. The vernier clamps d, 1, on the
latitude arcs D, L, have small holes or sockets formed in them to receive
This is a segment
the pins p of a loose angular distance segment C.
of a little larger radius than the latitude ares D, L, and it is marked with
degrees and is fitted with a vernier clamp a fitted with a projecting pin p,

page_text: whilst another pin p is fixed to the segment itself at the 90-degree point.
The pin p of the vernier clamp a is made movable in a radial direction to admit
of its being brought over the socket in the vernier clamp of the latitude
arc L
;
To ascertain longitude from a solar observation (for example) taken at any
convenient time, latitude being known, Greenwich time at the instant of the
observation is noted by the chronometer; one of the latitude arcs D is
clamped on the equatorial ring E to correspond to that time, and the vernier d
on this arc is set to the sun's declination as given in the Nautical Almanack for
that day. The vernier on the other latitude arc L is clamped at the latitude,
and the vernier a of the loose segment C is clamped at the altitude
ascertained by the solar observation, this causing the pins p to measure the
complement of the angle of altitude. The segment C is then set with one
pin p in the socket of the vernier clamp d marking the sun's place on the
arc D, already clamped on the equatorial ring E, and the other are L and
the segment C are manoeuvred until the other pin p of the segment C enters
the hole or socket of the vernier clamp / of this arc. This will fix the position
of the latitude arc L, and its vernier clamp e on the equatorial ring E will
mark the longitude sought. There are obviously two positions in which the
(second) latitude arc L may be set so as to give the same distance between
its vernier and that d of the other arc D, but the correct one will be to
the west or east of the sun's position accordingly as the observation is made
before or after noon.
If Greenwich time is sought, the longitude being known, also the latitude
and sun's declination, as in the case first herein-before described, then one
latitude arc L is clamped at the longitude on the equatorial ring E, and the
vernier on this arc is clamped at the latitude. The vernier d of the other
arc D is clamped at the sun's declination, and the segment C set as before to
the complement of the sun's altitude is applied to the two arcs, the unfixed
one D being moved until the pins p and the sockets in the vernier clamps
coincide. In a similar way, if the latitude is unknown, the other, elements
being known, the latitudo arc L will be clamped at its known longitude, and
its vernier will be moved until its socket can be got to coincide with the pin
of the segment C.
In order to ascertain latitude and longitude, both being unknown, two
observations are required to be taken, either simultaneously of two heavenly
bodies whose declinations are known, or at a known interval of time of the
sun. The apparatus must also be provided with a third latitude arc with

page_text: one vernier clamp for fixing on the equatorial ring E, and with another vernier
clamp having a socket for a pin.
Figure 8 is a Diagram in which the various pieces are indicated simply by
strong lines. The instrument may be constructed as shown in Figures 1
and 2, or in any other convenient way, provided the essential featuros herein
indicated are retained. The additional or third latitude arc M (Figure 3) is
like the other two D, L, and is hinged on the polar spindle P in a similar
manner. It may here be remarked that the necessities of construction, as
will be easily understood, require the arcs to be as it were mounted a little to
the sides of the lines they actually represent, in order that the pins or sockets
may always be in those lines. In the Diagram, Figure 3, however, the lines
represent those in which the pins and sockets move. The loose segment C
(Figure 3) has jointed to it at its 90-degree point a second limb N, as shown
separately in Figure 4, and this limb is fitted with a vernier clamp and pin n,
like the other limb. When using the two solar observations the vernier
clamps d, m, of the two latitude arcs D, M, are clamped at the sun's
declinations, and the arcs are clamped at points on the equatorial ring E
corresponding to the respective times of the two observations. The two
verniers a, n, of the hinged segments C, N, are clamped at the respective
altitudes, so as to measure from the joint pin the respective complements of
the two angles of altitude. The hinged segments C, N, are then set with the
two vernier pins in the vernier holes or sockets of the previously fixed latitude
ares D, M, when the pin at the hinge will mark the place at which the
observation is made; and on the latitude arc L being adjusted with the said
hinge pin in its vernier socket or hole this vernier will mark the latitude, and
the vernier connecting the arc to the equatorial ring E will at the same time
mark the longitude. With simultaneous observations of two heavenly bodies
the two latitude ares D, M, are clamped at the respective right ascensions on
the equatorial ring E, and their verniers d, m, are clamped at their respective
declinations. The hinged segments C, N, are then applied in the same way
as with the two solar observations. If the longitude is known, then the latitude
and Greenwich time can be ascertained in a similar way from two observations
of the sun with the elapsed time between them noted, or from two simultaneous
observations of different heavenly bodies.
It will be obvious that the details of construction of the apparatus may be
varied; thus the latitude arcs, or some of them, may be either within or
without the equatorial ring, and if the space within is occupied with &
terrestrial globe it will facilitate the adjustment of the arcs, and will enable

page_text: the user to realise the signification of the operations he has to perform. If
on the other hand it is desired to make the apparatus at as low a cost and to
go into as small a space as possible, the sizes of the parts may be reduced in
various ways, the fact that never more than 90 degrees have to be measured
at once allowing of this very conveniently.
.
Figures 5 and 6 are views at right angles to each other of an example of
the various possible modifications of this kind. In this modification the polar
spindle P has fixed in connection with it by means of arms a latitude
segment D, fitted with a vernier clamp d, having a socket for the sun's
declination. A latitude quadrant L, also fitted with a vernier clamp 7, is
constructed to be set on either end of the spindle P; it is represented as
placed to suit an observer's station on the further side of the equator from
the sun; but if the station and the sun are both on the same side it must
be set reverse ways on the other end of the spindle P. The operation is
the same as with the modification shown in Figures 1 and 2, except that
in the absence of the equatorial ring the movable segment L is clamped
(when its position is found) by means of pinching screws bearing on the
spindle. The loose segment C, which is the same as before, is then used
to measure the difference of longitude between the two segments D, L,
for which purpose the verniers on these are moved down to their equatorial
zero points, and the difference of longitude thus found being added to or
subtracted from that of the sun's place will give the longitude of the
observer's station. A third latitude segment may, of course, be adapted to
this modification.
It must be understood that in operating with our improved apparatus we
employ a measurement of the altitude of the sun which is corrected from the
observed altitude for the usual incidental errors, and in the usual way, and in
setting the apparatus to the time and sun's declination allowance is of course
made for any index or other errors the apparatus may itself have. In herein-
before explaining the use of the apparatus the observation dealt with has in
general been regarded as a solar one; it must, however, be understood that
observations of any heavenly bodies may be employed of which the
declinations and right ascensions are known from the Nautical Almanack or
otherwise.
Having thus particularly described our said Invention, and the manner in
which the same is to be performed, we have to state that we do not restrict
ourselves to the precise details herein described and delineated, but that what
we believe to be novel and original, and claim as the Invention secured to us

page_text: by the herein-before in part recited Letters Patent is, the ascertaining of
latitude, longitude, or Greenwich time by improved methods and apparatus
substantially such as are herein described and delineated.
In witness whereof, we, the said John Martin Rowan and Alexander
Morton, have hereunto set our hands and seals, this First day of
October, in the year of our Lord One thousand eight hundred and
sixty-six.
10 Witness,
EDMUND HUNT,
Patent Agent,
Glasgow.
JNO. M. ROWAN.
(L.S.)
ALEXANDER MORTON. (L.s.)