IMPROVEMENTS IN INSTRUMENTS FOR SOLVING PROBLEMS IN NAVIGATION
Year: 1876

page_text: LETTERS PATENT to Alexander Melville Clark, of 53, Chancery Lane, in the
County of Middlesex, Patent Agent, for the Invention of "IMPROVEMENTS
IN INSTRUMENTS FOR SOLVING PROBLEMS IN NAVIGATION." A communication
from abroad by Thomas Hill, of Portland, County of Cumberland, State of
Maine, United States of America.
Sealed the 1st September 1876, and dated the 26th April 1876.
PROVISIONAL SPECIFICATION left by the said Alexander Melville Clark
at the Office of the Commissioners of Patents on the 26th April 1876.
ALEXANDER MELVILLE CLARK, of 53, Chancery Lane, in the County of Middlesex,
Patent Agent.
"IMPROVEMENTS IN INSTRUMENTS FOR SOLVING PROBLEMS IN NAVI-
GATION."
This Invention relates to improvements in instruments for solving problems in
navigation hereafter described with reference to the accompanying Drawings, in
which,-
Figure 1 is a front view of the instrument.
Figure 2 is a front view in detail of the latitude circle.
Figure 3 is a front view in detail of the declination circle bearing a vernier.
Figure 4 is a top view of the hour angle circle.
Figure 5 is a face view of the altitude arc.
Figures 6 and 7 are under and upper views respectively of the compass card
attached to the altitude arc.
I will first describe the instrument and then its operation..
A, B, and C, D, are two meridians, the one marked latitude the other marked
declination, which are placed together in such a manner that the edges B, K, and
C, L, are in contact for their whole length, and the two meridians may open and
shut upon these edges as a hinge; F is a plate in the form of a sector of a circle
marked hour angle. To this plate the meridian C, D, is fastened at right angles
while the latitude meridian is set at any required angle with C, D, by the graduated
edge of F. On the latitude meridian are two hinge thumbs P, P, the lower one of
which plays in a hole M in the plate F; the upper one plays in a hole in the ear Q
at the top of the declination meridian C, D; the declination meridian bears a
vernier E carrying a steel pin at its vernier point; this vernier is movable upon
the arc of C, D. Both meridians are of the same radius and are graduated
from the pole Q down to thirty degrees below the equator at A and D.. G is an arc
[Pavice G71

page_text: of altitude graduated from two degrees below the horizon at O to the zenith H;
it is of precisely the same radius as the meridians, and bears at its zenith point a
compass card pierced at the centre with a hole to fit the vernier pin.
The use of the instrument is to solve the spherical triangle which is formed
when the zenith point H. is placed upon the pin of the vernier E, and the altitude
are laid across the latitude meridian. The sides of the triangle are known by
inspection, because they are graduated ares; the angle of the pole Q is measured
upon the graduated hour angle arc of F; the angle at E is measured by the compass
card attached to the zenith of the altitude arc. The third angle at the intersection
of the altitude arc with the latitude meridian remains to be measured, which
is done, not in the triangle itself, but in a symmetrical triangle formed by
moving the vernier pin to the latitude on the declination circle, and the altitude
arc to the declination on the latitude circle. The new triangle thus formed being
symmetrical with the old triangle the compass card now measures what was the
third or unmeasured. angle, and thus the triangle is. completely solved; in this
manner the instrument finds the time from an altitude taken by the sextant. The
vernier E is placed at the declination of the heavenly body observed, the zenith
point is put upon the pin, and the hour angle is altered until the observed altitude
on the altitude are exactly reaches the latitude of the observer. The hour angle is
then equal to the difference of the right ascension of the body and that of the
meridian, which gives at once the apparent time at the place of observation.
By making the altitude equal to zero this method gives at once the time of
sunrise and sunset. If in the same problems the symmetrical triangle is formed as
above described, the compass card gives the azimuth of the heavenly bodies
observed; the instrument also solves the problems of great circle sailing.
The meridians being clamped at an angle equal to the difference between the
longitude of the ship and of the desired port, the vernier E is placed on the decli-
nation meridian at the ship's latitude, the zenith of altitude is put upon it, and the
altitude arc laid over the latitude of the desired port. The compass card now
indicates the course while the co-altitude is the great circle distance. Thus the
navigator by this instrument can solve all the principal problems of navigation
relating to time, latitude, longitude, azimuth, and great circle sailing without the
labor and the liability to error of numerical or logarithmic computations.
SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Alexander Melville Clark in the Great Seal Patent Office on the 6th
October 1876.
ALEXANDER MELVILLE CLARK, of 53, Chancery Lane, in the County of Middlesex,
Patent Agent. "IMPROVEMENTS IN INSTRUMENTS FOR SOLVING PROBLEMS IN NAVI-
GATION." A communication from abroad by Thomas Hill, of Portland, County
of Cumberland, State of Maine, United States of America.
Figure 1 is a front view of the instrument.
Figure 2 is a front view in detail of the latitude circle.
Figure 3 is a front view in detail of the declination circle, bearing a vernier.
Figure 4 is a top view of the hour angle circle.
Figure 5 is a face view of the altitude arc.
Figures 6 and 7 are under and upper views respectively of the compass card
attached to the altitude arc.
I will first describe the instrument and then its operation.
A, B, and C, D, are two meridians, the one marked latitude and the other marked
declination, which are placed together in such a manner that the edges B, K, and
C, L, are in contact for their whole length; and the two meridians may open and
shut upon these edges as a hinge. F is a plate in the form of a sector of a circle,

page_text: marked hour angle. To this plate the meridian C, D, is fastened at right angles,
while the latitude meridian is set at any required angle with C, D, by the graduated
edge of F. On the latitude meridian are two hinge thumbs P, P, the lower one of
which plays in a hole M in the plate F. The upper one plays in a hole in the ear
Qat the top of the declination meridian C, D. The declination meridian bears a
vernier E, carrying a steel pin at its vernier point. This vernier is movable upon the
arc of C, D. Both meridians are of the same radius, and are graduated from the
pole Q down to thirty degrees below the equator at A. and D. G is an are of altitude
graduated from two degrees below the horizon at O to the zenith H. It is of pre-
cisely the same radius as the meridians, and bears at its zenith point a compass card
pierced at the centre with a hole to fit the vernier pin.
The use of the instrument is to solve the spherical triangle, which is formed
when the zenith point H is placed upon the pin of the vernier E and the altitude
are laid across the latitude meridian. The sides of the triangle are known by
inspection because they are graduated arcs. The angle of the pole Q is measured
upon the graduated hour angle arc of F. The angle at E is measured by the com-
pass card attached to the zenith of the altitude arc. The third angle at the
intersection of the altitude arc with the latitude meridian remains to be measured,
which is done, not in the triangle itself, but in a symmetrical triangle formed by
moving the vernier pin to the latitude on the declination circle, and the altitude arc
to the declination on the latitude circle. The new triangle thus formed being sym-
metrical with the old triangle the compass card now measures what was the third or
unmeasured angle, and thus the triangle is completely solved. In this manner tho
instrument finds the time from an altitude taken by the sextant. The vernier E is
placed at the declination of the heavenly body observed; the zenith point is put upon
the pin, and the hour angle is altered until the observed altitude on the altitude arc
exactly reaches the altitude of the observer. The hour angle is then equal to the
difference of the right ascension of the body and that of the meridian, which gives
at once the apparent time at the place of observation.
By making the altitude equal to zero this method gives at once the time of sunrise
and sunset. If in the same problems the symmetrical triangle is formed as above
described the compass card gives the azimuth of the heavenly bodies observed. The
instrument also solves the problems of great circle sailing.
The meridians being clamped at an angle equal to the difference between the longi-
tude of the ship and of the desired port, the vernier E is placed on the declination
meridian at the ship's latitude, the zenith of altitude is put upon it, and the altitude
are laid over the latitude of the desired port. The compass card now indicates the
course, while the co-altitude is the great circle distance. Thus the navigator, by
this instrument, can solve all the principal problems of navigation relating to time,
latitude, longitude, azimuth, and great circle sailing, without the labor and the
liability to error of numerical or logarithmic computations.
Having described the nature of the said Invention, and the manner of performing
the same, I declare that what I claim as the Invention to be protected by the
herein-before in part recited Letters Patent is,―
1st. The combination of three ares of equal radius, two convex and one concave, or
two concave and one convex, so combined as to form a spherical triangle, for the
solution of that triangle in problems of navigation or geodesy, as hercin set forth.
2nd. The attachment of a portion of a spherical surface and with a graduated
limb to one of the arcs as at H, as and for the purposes herein set forth.
In witness whereof, I, the said Alexander Melville Clark, have hereunto set
my hand and seal, this Thirtieth day of September, in the year of our Lord
One thousand eight hundred and seventy-six.
A. M. CLARK, (LIS:)