CERTAIN IMPROVEMENTS IN INSTRUMENTS FOR WHICH LETTERS PATENT WERE FORMERLY GRANTED TO ME, AND WHICH WERE CALLED THEREIN A NEW COMPASS FOR NAVIGATION AND OTHER PURPOSES, PART OF WHICH IMPROVE- MENTS ARE APPLICABLE TO INSTRUMENTS FOR MEASURING ANGLES AT SEA OR ON SHORE BY AID OF REFLECTION OR REFRACTION, OR OF REFLECTION COMBINED WITH REFRACTION, AND PART ARE APPLICABLE TO MAGNETIC COMPASSES FOR ASCERTAINING TRUE BEARINGS FROM CELESTIAL OBSERVATIONS, AND FOR COMPARING THE SAME WITH THE BEARINGS OF THE MAGNETIC NEEDLE CONTAINED IN SUCH COMPASSES, WHEREBY TO DETERMINE AND BE ENABLED TO ALLOW FOR THE DEVIATION OF SUCH NEEDLE FROM THE TRUE MERIDIAN, WHETHER BY VARIATION, LOCAL ATTRACTION, OR OTHER CAUSE OF ERROR
Year: 1839

page_text: TO ALL TO WHOM THESE PRESENTS SHALL COME, I, GEORGE
GRAYDON, of Sloane Street, Chelsea, in the County of Middlesex, Lieutenant-
Colonel of the Corps of Royal Engineers, send greeting.
WHEREAS I did by petition humbly represent unto Her present most
Excellent Majesty Queen Victoria, that after considerable application and
expense I had invented "CERTAIN IMPROVEMENTS IN INSTRUMENTS FOR WHICH
LETTERS PATENT WERE FORMERLY GRANTED TO ME, AND WHICH WERE CALLED THEREIN
A NEW COMPASS FOR NAVIGATION AND OTHER PURPOSES, PART OF WHICH IMPROVE-
MENTS ARE APPLICABLE TO INSTRUMENTS FOR MEASURING ANGLES AT SEA OR ON
SHORE BY AID OF REFLECTION OR REFRACTION, OR OF REFLECTION COMBINED WITH
REFRACTION, AND PART ARE APPLICABLE TO MAGNETIC COMPASSES FOR ASCERTAINING
TRUE BEARINGS FROM CELESTIAL OBSERVATIONS, AND FOR COMPARING THE SAME
WITH THE BEARINGS OF THE MAGNETIC NEEDLE CONTAINED IN SUCH COMPASSES,
WHEREBY TO DETERMINE AND BE ENABLED TO ALLOW FOR THE DEVIATION OF SUCH
NEEDLE FROM THE TRUE MERIDIAN, WHETHER BY VARIATION, LOCAL ATTRACTION,
OR OTHER CAUSE OF ERROR;" and Her said Majesty, being willing to give
encouragement to all arts and inventions which may be for the public good,
was graciously pleased, by Her Royal Letters Patent, under the Great Seal of
the United Kingdom of Great Britain and Ireland, bearing date at West-
minster, the Twenty-fourth day of October (1839), in the third year of Her
reign, for Herself, Her heirs and successors, to give and grant unto me, the
said George Graydon, my executors, administrators, and assigns, Her especial
license, full power, sole privilege and authority, that I, or they, by myself
or themselves, or by my or their deputies, servants or agents, or such others as

page_text: I or they should agree with, and no others, during the term of fourteen years
from the date of the said Letters Patent, should and lawfully might make,
use, exercise, and vend my said Invention within that part of Iler said
Majesty's Dominions called England, Her Dominion of Wales, and Town of
Berwick-upon-Tweed, and also in all Her said Majesty's Plantations and
Colonies abroad, in such manner as to me, my executors, administrators, and
assigns, shall seem meet, and as that I or they shall enjoy the whole profit
and advantage arising by reason of the said Invention during the said term of
fourteen years;
and for that end Her said Majesty requires and strictly
commands all Her subjects whatsoever, within England, Wales, and Berwick-
upon-Tweed, and in the Colonies and Plantations abroad, aforesaid, that they
shall not, neither directly nor indirectly, make, use, or put in practice my said
Invention or any part thereof, nor in anywise counterfeit, imitate, or resemble
the same, nor make any addition thereto or subtraction therefrom whereby to
pretend himself or themselves to be the inventor or inventors thereof; and
whereas the said Letters Patent contained a proviso obliging me, the said George
Graydon, particularly to describe and ascertain the nature of my said Inven-
tion, and in what manner the same is to be performed, by an instrument in
writing under my hand and seal, and to cause the same to be enrolled in
Her Majesty's High Court of Chancery within six calendar months next and
immediately after the date of the said Letters Patent, as in and by the same,
reference being thereunto had, will more fully and at large appear.
NOW KNOW YE, that in compliance with the said proviso, I, the said
George Graydon, do hereby declare that my said Invention is described and
ascertained in manner following, and by the aid of the three Sheets of
Drawings hereunto annexed, that is to say :-
The said Drawings represent complete instruments constructed according to
my said improvements, and I will first describe these instruments and then at
the conclusion of this Specification I will point out the particulars of new
Invention whereof the exclusive use is granted to me by the aforesaid Letters
Patent.
In Sheet I. of the Drawings hereunto annexed, Figures 1, 2, and 3 represent
a compass for use on board ship or on land, which I have named a celestial com-
pass; because it indicates true bearings or horizontal angles with the meridian by
observation of celestial bodies, without any dependance upon the magnetic needle
or upon a view of the horizon. Figure 1 is a section, Figure 2 an elevation, and
Figure 3 a horizontal plan, of the compass, and Figures 4 and 5 are perspective
views of the parts detached., A, B, is the wooden box, wherein the instrument
is enclosed; the upper portion of each of the four sides of the box is made to

page_text: turn down on hinges in order to leave the upper part of the instrument suffi-
ciently exposed for use. The box A, B, is mounted so that it can be turned
round horizontally on a central pivot or short upright fixed axis C, Figure 1,
which is received into a central socket in the bottom of the box. That upright
axis C is either fixed fast into a base or board D, which is fixed on a stool or frame
at a suitable height above the deck of the ship, or else, when the instrument is
to be used on land, the said upright axis is the upper part of a tripod stand E,
which will sustain the instrument at a suitable height above ground for making
observations with it. The box A, B, being capable of turning round hori-
zontally about the said fixed upright axis C, with an easy motion as may be
required in order to present the upper part of the instrument to the celestial
bodies which are to be observed. F is the bowl containing the magnetic
needle and compass card suspended on a centre point so as to turn round freely
within the bowl, which is covered over with a glass in the usual manner of
compasses. The bowl F is suspended within the box A, B, by the intervention
of a set of gimbal rings one within another, and having pendulous weights
applied to some of the rings in such manner as that the tendency of one ring
and its weights to oscillate in the manner of a pendulum will be counteracted
by the like tendency of another of the said rings and its weights; in order that
the bowl F (which is suspended within all the said rings having also a pen-
lulous weight I applied to it) may retain a quiescent horizontal position,
notwithstanding that the external box A, B, will partake of the motion of the
ship; the outermost of the gimbal rings a, a, is suspended on two pivots
which project out horizontally from short bars b, b, that are fixed obliquely
across two angles of the box A, B; those pivots are fixed, pointing one
towards the other, and they enter into holes at two opposite points of the
circumference of the ring a, a, in order to suspend the same and form its axis
of motion; and at two other intermediate points in the said ring a, a, are
pivots g, g, which suspend a pendulous weight f, f, by the upper ends of
curved arms e, e, belonging to that weight, which weight is in the form of
a heavy ring f. f, the centre of gravity whereof will be at a considerable
distance beneath the horizontal centre line between the suspending pivots
9, 9, so that the heavy ring f. f. as suspended by its curved arms e, e,
from those pivots g, g, forms a pendulous body; and the said heavy ring
ff, has also two other curved arms h, h, ascending upwards from it, n order
to sustain pivots i, i, at their upper ends at the same level with the suspending
pivots g. 9, on which pivots i, i, an interior gimbal ring k, k, is suspended at
two opposite points in its circumference, the line between these two points i, i,
forming the axis of motion of the ring k, k, the direction line i, i, of the

page_text: said axis of motion being at right angles to the direction of the line between
the pivots g, g, by which the heavy ring f, f, is suspended from the outer
ring a, a, to form the axis of motion of that heavy ring f, f, but the said direc-
tion line i, i, is in the same direction as the line between the fixed pivots at b, b
on which the outermost ring is suspended. Note.-The said heavy ring f.f,
having four rigid arms e, e, and h, h, proceeding upwards from it, and with
pivots at the upper ends of each of those arms, all those pivots being in one
plane, and the four pivots forming two axes of motion crossing each other at
right angles, and on one of which axes the heavy ring itself and its four arms
is suspended within the outermost gimbal ring a, a, and on the other of those
axes the inner gimbal ring k, k, is suspended, wherefore the said heavy
ring ff, with four arms c, c, and h, h, performs the office of another additional
gimbal ring if such a one were interposed between the outermost gimbal ring
a, a, and the inner one k, k, and by the pendulous weight of the heavy ring
ff, the said supposed additional or intervening gimbal ring has a tendency
given to it to retain a horizontal position. This construction being explained,
it may be easily understood that the ring h, k, has suspended within it
another four-armed piece 1, 1, 0, 0, of the same nature as the four-armed heavy
ring f, f, aforesaid, and for a like purpose of suspending within two of its arms
an innermost gambal ring m, m, except that the pendulous weight n of
the four armed piece 1, 1, o, o, is situated lower down than the heavy ring
ff, that weight n being hollow and fixed on the lower end of a central tube
which passes down through the aperture of the heavy ring ff; wherefore the
four armed piece 1, 1, 0, 0, and its hollow pendulous weight n (considered as
an oscillating body) will have a tendency to vibrate more slowly than the four-
armed heavy ring f.f. The four-armed piece 1, 1, 0, 0, is suspended by two of its
arms 1, 1, on pivots in the ring k, k, at two opposite points of the circum-
ference of that ring, the line between those points forming the axis of motion
for the four-armed piece l, 1, 0, 0, and the direction of the said line being the
same as the direction of the line between the pivots g, g, on which the heavy
ring f, f, is suspended within the outermost gimbal ring a, a; the other two
arms o, o, of the four-armed piece 1, 1, 0, 0, have pivots to suspend the innermost
gimbal ring m, m, at two opposite points of the circumference thereof, the line
between those points being in a direction at right angles to the direction of the
line between the pivots of the other two arms 1, 1, of the four-armed piece 1, 1, 0, 0,
and on which last-mentioned pivots that piece is suspended. And, lastly, the
bowl F is suspended within the innermost gimbal ring m, m, upon pivots at two
opposite points of the circumference of that ring, entering into pivot holes in
the two ends of a cross bar G, which extends horizontally across over the glass

page_text: cover of the bowl F, and the circumference of the bowl is fixed fast to the
bar G, which has also a branch I projecting out from the middle of it like the
letter T, and reaching over the glass cover of the bowl from the centre thereof
to the circumference of the bowl, where the same is made fast to the end of
that branch I, so as to assist in uniting the bowl F firmly to the under side of
the bar G. But note.-The said branch I of the bar G does not reach so far
as to touch the innermost gimbal ring m, and therefore the bowl is at liberty
therein to swing freely on the pivots at the ends of the cross bar G; and
from the bottom of the bowl F, a long slender stem p, which is fixed fast
thereto, descends through the interior of the before-mentioned central tube of
the hollow pendulous weight 2 of the four-armed piece 1, 1, o, o, and on the lower
end of the stem pa pendulous weight H is fixed, and tends to keep the bowl G
steady with its glass cover and the cross bar G, and the branch I thereof in a
horizontal plane, notwithstanding that the external box A, B, may be par-
taking of the motion of the ship. For the heavy ring f, f, and the four-armed
piece 1, 1, 0, 0, with its hollow pendulous weight 2, and the stem p, and the
pendulous weight II of the bowl F form, three independent pendulous bodies,
each of which is suspended gimbal fashion so as to admit of vibrating freely
in any possible direction about a common central point of suspension, which
is situated a little above the centre of the glass cover of the bowl F,
being in the comuion centre of all the several gimbal rings a, a, k, k, and
m, m, and exactly at the interstices of the several lines of direction between
the opposite suspending pivots in those rings; but the heavy ring f, f, being
nearer to the said central point of suspension, forms a short pendulum adapted
to quicker vibration than the four-armed piece 1, 1, o, o, which having its
hollow pendulous weight beneath the heavy ring f, f, forms a longer pen-
dulum adapted to slower vibration, and again the pendulous weight H of the
bowl F, being beneath the hollow pendulous weight n, forms a still longer pen-
dulum adapted to still slower vibration. The interior opening of the heavy
ring ff, is so much larger than the central tube of the four-armed piece 1, 1,
o, o, which passes down through the said ring, as is sufficient to adniit of a
considerable latitude of pendulous motion of the ring f, f, in any direction
without causing interference or contact between the ring and the tube. And
likewise, the interior of the said central tube is so much larger than the slender
stem p of the bowl F, which passes down through the tube as will allow the
tube as much latitude of pendulous motion as it is likely to require without
causing any interference or contact between the tube and the stem.
note. The hollow pendulous weight n is fitted on the outside of the tube with
a nut below it screwed upon a screw thread, which is cut on the outside of the
And

page_text: tube, so that by turning that nut the hollow weight n can be placed bigher up
or lower down on the tube, in order to adjust the length of pendulum formed
by the four-armed piece 1, 1, 0, 0, and its hollow weight as may be found
desirable. And in like manner the slender stem p has a nut screwed upon a
screw which is cut on the lower end of that stem, so that by turning the said
mut the pendulous weight H can be placed higher up or lower down on the
stem in order to adjust the lenght of pendulum formed by the bowl F, and its
weight H.
A small door is provided at the lower part of the box A, B, to
admit the hand for turning the said nuts in order to adjust the pendulums
when requisite, such adjustments being made experimentally until it is found
by repeated trial, and watching the result and re-adjusting according thereto,
that the greatest steadiness of the bowl F is attained, but no other rule can
be given for making such adjustments, because they must be adapted to
the degree and kind of motion which the particular ship wherein the
compass is used is liable to undergo. The Drawings Figures 1, 2, and 3
represent the instrument half its real size, and the instrument being
made according to the Drawings, the aforesaid adjustments of the weight
being duly made experimentally, will enable the instrument to preserve
a steady horizontal position of its bowl F, for the motion which will be
given to the box A, B, by the ship will be only in part communicated to the
four-armed heavy ring f, f, because the same by its gravity will have a
tendency to remain steady, but as that tendency will not keep it completely
steady, it will be urged into a small extent of oscillating motion; and
whereas the four-armed piece 7, 1, o, o, with its hollow weight n, derives its
support entirely from the heavy ring f, f, the said four-armed piece will only
be very slightly urged to oscillation because it has no direct communication with
the external box at B, and therefore only that small portion of the motion
thereof which is communicated to the heavy ring f. f, can become operative
on the four-armed piece so as to disturb its tendency to quiescence and urge it
to oscillation, and whatever oscillations the heavy ring f. f, may be caused to
perform by the agitation of the box A, B, they will incline to be quicker
vibrations than the four-armed piece 1, 1, o, o, is disposed to perform, because
the latter is a longer pendulum than the former; hence the tendency of the
motion of the box A, B, to produce oscillation of the four-armed piece will be
greatly reduced in extent, and will be greatly interrupted and counteracted in
that small extent to which it is operative by the intermedium of the heavy
ring f, f, owing to a disinclination of the four-armed piece to perform simul-
taneous or concurrent vibrations with those that the heavy ring f, f, may be
caused to perform; and again, the like may be said of the bowl F, with its

page_text: pendulous weight II. As the same forms a longer pendulum it has a greater
tendency to remain quiet in a vertical position, and if it were urged into oscilla-
tory motion, it would be to perform slower motions than the four-armed piece
1, 1, 0, 0, is disposed to perform, and as the bowl F and weight H derives its
support entirely from the said four-armed piece, without any direct connection
with the box A, B (except by the intermedium of the heavy ring f, f, in the first
place, and therefrom by the four-armed piece 1, 1, o, o, in the second place), the
motion of the box A, B, becomes so very much diminished in the transmission
from the box to the heavy ring, and then from the heavy ring to the four-armed
piece, that the tendency of the latter to communicate motion to the bowl F and
weight H being also counteracted by the want of harmony in their dispositions
to vibrate together, the said tendency will not be able to overcome the tendency
of the bowl and weight H to remain quiescent so far as to produce any sensi-
ble motion thereof; but the same will remain sufficiently steady with its glass
in a horizontal plane for taking celestial observations with the apparatus at the
upper part of the instrument; that is to say, in very tempestuous weather the
motion of the box A, B, may be so great that all the diminution and counter-
action which it will undergo by transmission through the heavy ring f, f, and
the four-armed piece l, 1, 0, 0, as already explained, may fail to sufficiently
enfeeble the tendency to urge the bowl F and weight H into motion, but the
same will be caused to oscillate sensibly; nevertheless, in moderate weather,
and under ordinary circumstances, the bowl will retain suflicient steadiness
for making useful observations with the instrument, although with less pre-
cision as the motion of the ship is more violent, and with more precision as
the ship is more steady. And much of the precision will depend upon seizing
a favourable moment for taking an observation when the bowl is most steady,
because the tendency to motion on board ship is continually varying, and
periods of sufficient tranquillity may be commonly found for taking very useful
observations with the instrument, except in very rough weather; and even
when the bowl F has a slight oscillating motion, the error that would in
consequence be occasioned in an observation by the departure of the bowl
from its assumed horizontal position may be in a great part neutralized by
watching the instrument during its oscillation whilst an observation is making,
in order to find when it gives the greatest and least indications of the angle
that is to be observed, and then a mean between those extremes may be
chosen as the angle that is to be recorded. And note. All the several pivots of
suspension and pivot holes for the gimbal work above described should
be made of hard material, such as bell metal or agate, and delicately
formed so as to move with the least possible friction, in order that there

page_text: may be the less tendency to transmit motion from each gimbal ring to
the other that is suspended within it. Or the said pivots may be made
in the manner of what are termed knife-edge suspensions, such as are
commonly used for the centres of suspension of scale-beam balances. The
several gimbal rings should be made as light as is consistent with the requisite
strength, and so of the bowl and other suspended parts (except the several
pendulous weights themselves); they should be light in order that there may
be less friction on the suspension pivots, and also in order that the several
pendulous weights (viz., the heavy ring f, f, and the hollow weight n, and the
weight H,) may predominate so decidedly over the weight of all the other
suspended parts, as to be the less susceptible of being disturbed and put into
motion from the tendency to motion in those other parts, which parts, in conse-
quence of being at a higher level than the several pendulous weights, are less
influenced by gravitation to keep them steady. The upper parts of the instru-
ment wherewith the observations are to be made are mounted upon the cross-
bar G, which has been already mentioned as having a branch I like the
letter T, and as having the bowl F fastened to its under side. The upper
surface of the said cross bar G is kept steady in a horizontal plane by gravita-
tion of the pendulous weight II of the bowl F, as already explained. There is
a transverse notch made near to each end of the cross bar G, to receive two
ears which project downwards from the under edge of a divided circle or
ring K, and pins are inserted horizontally across the said notches, and through
the said ears to form joints whereof the two may be considered as constituting
a horizontal axis on which the circle K is supported, and to which circle that
axis forms a diameter, and about which axis the said circle can be tilted up in
order to place its plane in a vertical position, or it can be turned down to place
its plain in a horizontal position, over and around the glass cover of the
bowl F, or the circle K can be tilted to place its plane at any degree of
inclination between horizontal and vertical, in order that it may at any time
be placed in a position parallel to the equator, wherefore it is called the
equatorial circle or the hour circle, the latter name being because its circum-
ference is divided into twenty-four hours with subdivisions. The hour circle K
is upheld at any required inclination, as aforesaid, of its plane by means of a
quadrantal divided arch L, which is affixed to the circumference of the
circle K at a point equidistant from the two joints by which the said circle is
supported on the cross bar G, the arch L descends from that point of the
circle K, around the under part of the bowl F, when the circle K is turned
down to place it horizontally, and the arch L is received in a clamp t, attached
to the end of the branch of I, the cross bar G, so that by screwing that clamp.t

page_text: it will pinch and hold fast the arch L, in order to retain the hour circle K at
its intended inclination, and the said clamp is attached to the end of the said
branch I by intervention of a slider which is moveable by means of a slow-
motion screw v, in order that by turning the said screw v, after the clamp t is
screwed tight to clamp the arch L, the circle K can be slowly and exactly
regulated in order to place its plane at the required inclination. The angle of
such inclination from the horizontal plane is indicated by divisions of degrees
engraved on the arch L, and for subdivision of those degrees they apply
against a vernier on a suitable piece w affixed to the end of the branch I of
the cross bar G. When the hour circle K is turned down horizontally, the
vernier of the said divisions will read zero, and when the circle K is turned up
vertically the said vernier will read ninety degrees, wherefore the said divisions
represent degrees of latitude; and the circle K being first inclined until the
vernier reads the degree and minute of latitude of the place where the instrument
is at the time of being used, & next the whole box A, B, being gently turned
round about its supporting pivot or axis C, Figure 1, until the arch L is in the
meridian (towards the south in northern latitudes, or towards the north in
southern latitudes), then the plane of the hour circle K will become parallel
to the earth's equator, and the twenty-four hours into which it is divided will
answer to the progress of the sun in the heavens during the several hours of the
day. That is the case on the days of vernal and autumnal equinox or else with
due allowance on all other days for the difference then existant between mean
solar or clock time and apparent or sun dial time. These particulars being
understood the other moveable parts of the instrument may be explained.
Above the hour circle K another moveable circle V is applied, and accurately
fitted by means of a circular groove, and rebate so as to turn round thereon,
and the moveable circle V is provided with suitable guides to retain it in its
place upon the circle K. The moveable circle V has a vernier scale engraved
upon it, to apply to the divisions around the hour circle K, and sub-
divide them, and from one part of the circumference of the said moveable
circle a radial bar W extends to the common centre of the two circles
K, V, and there the said radial bar W carries a small centre pin with a
spherical knob, which is received into a corresponding hollow in the middle
of the cross bar G. The centre of the said spherical knob and of the hollow
being precisely in the horizontal line between the two joint pins at the ends of
the cross bar G, which line has been already mentioned as an axis on which
the hour circle K is supported; by this means the said centre pin forms the
centre of motion for the radial bar W, when the same moves round about
the hour circle K, along with the upper moveable circle V, and in consequence

page_text: of the spherical form of the knob r and its socket, the said centre of motion
continues undisturbed by any elevation that may be given to the hour circle K.
Upon the upper side of the said radial bar W a forked standard U is fixed up
and rises up over the aforesaid centre of motion to support a small declination
circle, whereof the plane is at right angles to the plane of the hour circle
K, and which circle M is included between the prongs of the fork U, and
its centre pivots are supported thereby forming the axis of motion for the said
circle M, the direction of that axis being parallel to the plane of the hour
circle K. The small declination circle M is hollow within in the manner of
a box, and the telescope N, by which observations of celestial bodies are
taken, is fixed with one end entering into the hollow of the circle M, the other
end N, which is the object glass, projecting out therefrom; at that end of the
telescope which is within the box, a diagonal eye piece O joins to the telescope
and projects outwards from the small circle M in a direction at right angles
to the direction of the telescope N, which arrangement is for the convenience
of applying the eye at O to look downwards towards the centre of the radial
bar W and of the bowl in order to observe any object to which the object end N
of the telescope is directed. The declination circle N is divided with degrees
around its flat surface near the circumference thereof, and an index mark is
borne by the upper end of one of the prongs of the forked standard U, in
which the pivots of the circle M is mounted. The said divisions indicate zero
when the direction of the telescope N is exactly parallel to the plane of the
hour circle K, as is represented in Figure 2; and any celestial object which
is then seen through the telescope N by looking into its diagonal eye piece O
will be in the celestial equator or equinoctial and will have no declination, but
if by turning the declination circle M the telescope N is inclined either
upwards or downwards from the parallelism aforesaid, the number of degrees
of such inclination will be indicated by the divisions on the circle M, so as to
give the amount of north declination or south declination (as the case may be)
of any celestial object which may be observed through the telescope. The
aforesaid index mark of the declination circle M may be a vernier, which will
subdivide the divisions or degrees on that circle, or otherwise the requisite sub-
division may be obtained by a tangent screw P, which is applied to act in
teeth cut round the circular edge of the declination circle M, and having a
micrometer head on the axis of the screw. By turning that screw P round
a slow motion is given to the declination circle and to the telescope, so as
to elevate or depress it to the declination of the celestial object which is to be
observed. The motion of the aforesaid radial bar W, and upper moveable
circle V around the hour circle K, enables the telescope to be directed to any

page_text: celestial object which is out of the meridian, and the divisions of the hour
circle will indicate the meridian distance or hororary angle of the celestial
object which is observed through the telescope, for when the radial bar
W is over the arch of latitude L then the telescope is in the meridan, as is
represented in Figure 3, and then the divisions of the hour circle K will be at
their zero (which is also marked twelve o'clock), and from that zero the
degrees are reckoned in order to indicate hororary angles with the meridian, or
the hours and subdivisions are reckoned to indicate time. The uses of this
instrument are numerous, being for the most part the same as those purposes
to which a portable equatorial instrument is or may be applied on shore, but
which purposes can by this instrument be performed on board ship with suffi-
cient accuracy to be of great use to navigators, and in particular to determine
the true meridian independantly of the magnetic needle, and as such a needle
is contained in the bowl F in the usual manner of ships' compasses the
deflection of that needle from the true meridian can be ascertained from
time to time, and under all the varying circumstances of local attraction by
reference to celestial observations so as to inform the seaman what allowance
he ought to make in the several bearings indicated by the magnetic needle
to enable him to steer truly any intended course. For this purpose the
instrument may be used in manner following:-The hour circle K is first to be
inclined by aid of the arch L to suit the latitude of the place where the
observation is about to be made; then the telescope N is to be inclined by
aid of the divisions around its declination circle M to suit the declination
(north or south, as the case may be,) of the celestial object by which the
observation is intended to be made. Suppose it is the sun, and then the
moveable circle V above the hour circle K is to be turned round to suit.
the hour and minute of the day, when the observation is to be made, that hour
and minute, being reckoned in apparent solar or sundial time; and then, after
so setting the instrument it is to be turned horizontally round about the
upright axis C, Figure 1, at the bottom of the box A, B, on which axis
the whole is sustained until the celestial object in question is brought into
view through the telescope, and then at the precise time of day which is
indicated, as before mentioned, upon the hour circle K, the vertical plane
passing through the zero or twelve o'clock division in that circle K, and also
through the centre r thereof, will be in the true meridian; and there being a
mark (commonly called by seamen the lubber's mark) within the bowl F,
exactly beneath or in the same vertical plane with that zero or twelve o'clock
line, such mark will indicate, by the usual divisions around the circumference
of the compass card, the exact number of degrees of variation or deflection of

page_text: the magnetic needle from the true meridian. And in order to find what
allowance should be made on account of local attraction in the vessel a series
of such trials, as aforesaid, must be made with the vessel's head directed to all
different quarters and points of the horizon in succession, and the variation or
deflection of the needle in each of her different positions being thus ascertained,
may be recorded in a table to form a scale of varying allowance to be made in
compensation for the deflection or error of the needle in future, when steering
on each different course; or, instead of the sun, the moon may be observed in
the manner aforesaid, or any remarkable star which is in or near the zodiac;
the time to which the vernier of the hour circle K is set, being in such cases
reckoned in lunar or siderial instead of solar time. In all cases of taking
observations by the instrument, if precision is desired, due allowances are to bo
made for the effects of refraction, and for the semidiameter of the sun or moon,
according to the usual custom of astronomers in like cases, and which being
well known does not require further explanation. Another use of the instru-
ment is, for taking altitudes of celestial bodies above the horizon for the same
purposes as is usually done by the sextant, but which is done by this instru-
ment without any reference to the visible horizon, whereas in cases when
that horizon is obscured by fog or mist, such altitudes cannot be taken by the
sextant. The declination circle M may for such purpose be set at zero, so that
the telescope N will be parallel to the plane of the hour circle I, and the
circle V upon that hour circle is to be set to zero or twelve o'clock, so that the
telescope will point exactly over the arch of latitude L; the instrument
being thus prepared is to be turned altogether round about its upright axis C,
Figure 1, to direct the telescope towards the celestial object whereof the
altitude is to be determined; and then the hour circle K, together with
the telescope N being elevated (and adjusted by aid of the slow-motion screw v
of the arch L) until the telescope is brought to observe the object exactly, the
divisions of the arch L will give the required altitude of the object above
the horizon. The effect of refraction will of course be required to be allowed
for, as usual in taking altitudes; also the sun's or moon's semidiameter, if they
are observed, but the usual allowance for dip of the horizon will not be
required, as the horizon is not in question. And whereas the exactitude of all
observations made with the instrument will depend upon the horizontality of
the bowl F and the cross bar G, which is fixed over the bowl, and which, with
its branch I forms the basis for all the upper parts of the instrument that
horizontally must be accurately adjusted in the first instance, and verified from
time to time in manner following:-The hour circle K must be turned
down into its horizontal position over the bowl F until the arch L of

page_text: latitude is at its zero, then the declination circle M may be set with the
telescope N inclined downwards as much below the zero of the divisions as is
suitable for the dip of the horizon, according to the height of the instrument
above the level of the sea, in which case, if the instrument is truly horizontal
the horizon will be seen through the telescope, and on turning the moveable
circle V that is above the hour circle K successively round to view all
quarters and points of the horizon, the horizon ought to be seen through the
telescope alike in all cases; but if it does not, and some part of the horizon
appears higher and other part lower, then the instrument must be adjusted
truly, which may be done by means of four small balancing weights fastened
to the four quarters of the circumference of the bowl F, for by reducing one
or other of such weights the balance of the bowl may be rendered true, or the
cross bar G may be adjusted truly level over the bow! F by means of setting
screws, by which it is affixed to the bowl F. And note.-In order to shew
whether the instrument, after having been so adjusted, will retain its said
horizontality, two or four small spirit levels may be fastened by screws, and
with setting screws, to the circumference of the bowl Fat places ninety
degrees asunder around that circumference, the tubes of the levels being in
directions at right angles one to the other; and when the instrument is cor-
rectly adjusted, those levels being set by their setting screws, so as to have
their bubbles in the midway of the lengths of their tubes, will always after-
wards shew whether the instrument continues in adjustment; for whenever
an observation is made, the said two spirit levels being examined, will shew
if the instrument continues horizontal, so that it may be depended upon, or
whether it is become deranged, and requires to be new adjusted. And note.―
In order to avoid derangement of the balance, and consequent horizontality of
the instrument, by the weight of its own moving parts, when the same are
placed in different positions, each of these moving parts must be very exactly
balanced by disposing equal weight on opposite sides of that particular centre
of motion, around which each moving part is appointed to turn or move;
for instance, the telescope N, with its diagonal eye piece O, & the small
declination circle M, must be balanced by applying weight within the hollow
of that circle at the under side thereof, so as that the whole of the aforesaid
parts taken together will form a true equipoise about the centre of motion
or axis of the declination circle M, on which axis they are all mounted,
and about which they are to perform their movements for declination. Again,
the moveable circle V, which is applied and fitted upon the hour circle K,
must have as must weight applied to its circumference on the side opposite to
its radial bar W as will counterpoise that radial bar, and the forked standard

page_text: U thereon, which supports the declination circle and telescope, together with
that circle and telescope, and the tangent screw P, so as that the said moveable
circle, together with its said appendages, will form a true balance on its
centre.
And, lastly, the lower end of the arch of latitude or altitude L must be
prolonged so far round the bowl F, and have as much weight applied to it,
as will counterpoise the hour circle K with the moveable circle V that is
fitted thereon, and the radial bar W of that circle V, together with the decli-
nation circle, telescope, and other parts above mentioned, which are borne
by that moveable circle, so as that the said arch L, with its counterpoise,
and the said circle K, and the moveable circle with its said appendages,
will balance truly about the central line or horizontal axis formed by the
two pivots or joint pins by which the hour circle K is sustained, and applied
upon the cross bar G, as before explained. And note.-It is obvious that the
lighter the telescope, declination circle, hour circle, and other upper moving
parts above described can be made, consistently with strength, the less weight
will be required to produce the counterpoise aforesaid, and the more effec-
tually the bowl F will be able to keep a steady quiescent position by the
gravitation of its pendulous weight II, because the lighter all the upper
moveable parts can be made, the less they will be able to counteract the
tendency of that gravitation. And note.-The slender stem is affixed to
the bottom of the bowl F by means of a cranked or bended piece of metal x,
which will admit the lower end of the arch L of latitude or altitude to pass
beneath the centre of the bowl F, although the stem p is situated in the
central line of the bowl when prolonged downwards. The instrument may be
used to take the altitude of the pole star in the same manner as already ex-
plained for taking the altitude of any other celestial body, and the altitude so
obtained may be used for finding the latitude of the place of observation in
the same manner as would be done if the like altitude had been taken in the
ordinary manner by a sextant. But to facilitate the determination of the
latitude by observation of the altitude of the pole star with the instrument it
may have a glass wedge or prism applied over the object glass of its telescope
N in the manner of an additional object glass to that telescope. The said
wedge is a piece of glass whereof the two opposite sides are plain surfaces, but
are not parallel, being inclined one to the other, with a slight obliquity, where-
fore the rays of light which pass through such glass are refracted or slightly
bended from a straight course, and the glass is adapted to bend the rays at
just such a small angle (viz., about one and a half degrees), as the angular
distance of the pole star from the true pole being what is termed the polar

page_text: distance of the pole star, wherefore, when such a glass is applied over beyond
the object glass of the telescope, and the pole star is viewed through the tele.
scope and through the glass wedge, the central line of collination of that tele-
scope will not be directed towards the pole star, as would be the case without
the wedge of glass, but the telescope will be directed towards the true pole,
owing to the glass wedge bending the ray of light from the star at the point
where it enters into the telescope just as much in angular measurement as the
pole star is distant from the true pole in such measurement. The ring or cell
wherein the said glass wedge is fixed, and which is mounted over the object
glass end of the telescope, is adapted to turn round about the axis of the tele-
scope as a central line or axis of motion, and the circumference of the ring is
marked with divisions denoting twenty-four hours, those divisions being so
numbered in respect to the glass wedge as that when the cell is turned round
about the object glass of the telescope to the division for any hour (reckoned
in syderial time), then when that hour arrives and the telescope is directed to
point to and see the pole star, then the direction of the telescope will be
truly parallel to the axis of the earth, and will consequently be in the meridian,
and the altitude or angle of elevation of the telescope above the horizontal will
be indicated by the divisions on the arch L of latitude or altitude, and will be
the latitude of the place of observation without other correction than for
refraction. And whereas the telescope when so directed to the true pole, as
aforesaid, will also be in the true meridian, the variation or deflection of the
magnetic needle therefrom will be pointed out on the degrees around the com-
pass cards by the lubber's mark withinside of the bowl F.
In Sheet II. of the Drawings hereunto annexed, Figure 6 is a perspective.
view, and Figure 7 a section, of another celestial compass, which has all the
same properties as that already described and represented in Sheet I., but which,
is very different in the construction of its suspension parts and its pendulous
weights, although in operation and principle of action the pendulous weights are
much the same, the ground of the difference being that instead of suspension of:
the parts by their exterior circumferences in gimbal rings upon pivots forming.
centre lines of motion, in order that such centre lines by intersecting one,
another may admit of free pendulous motion of the suspended parts in all direc-.
tions about one common central point of motion, and suspension, instead thereof,
the suspension of each pendulous weight is made upon a single central point
situated within the interior of the suspended part, and at (or as nearly as possible.
at) the place where the aforesaid common central point of suspension would be.
if the suspension were made gimbal fashion as in Sheet I., wherefore such sus-
pension upon single points (as in Sheet II.) admits of a free pendulous.

page_text: motion of each pendulous part in all directions, but such motion about one
point will be performed with less friction than would be caused by the four
pivots which are required to effect the same purpose by a gimbal ring in the
manner of Sheet I., and also the weight of that ring is avoided, all which are
advantageous in favour of the construction Sheet II., which requires a totally
different form of all the parts in order to admit the suspending points into the
interior of each pendulous part. This cause of difference in construction and
similarity of action between the two being understood, the description of
Sheet II. is as follows:-A, B, is the external wooden box which opens by its
four sides turning down on hinges; C, the upright fixed axis on which it is
mounted; D, Figure 8, is its base or board to support it on a stool, or else E,
Figure 7, is its tripod stand, all similar to the corresponding parts in Sheet I.;
b is a bracket partly of wood and partly of metal fixed into one of the angles
of the box, and reaching out therefrom to the centre, where it sustains the
base of an upright pillar d (see Figure 7), so as to hold the same firmly
in its upright position, and the upper end of the pillar d is a conical
point g of hard bell metal, and upon that point is poised the pendulous
weight ff, which is an obtuse hollow cone made of thin copper covered
with lead; an agate is fixed in the vertex of the cone f, f, to rest upon the
fixed point g, and the cone f, f, is freely at liberty to move or vibrate in all
directions about that fixed point g; no part of the cone f,f has any connection
or contact with any other part, except that point g, and also a contact with the.
suspension point k of the next pendulous weight n, n. That point rests upon
the upper surface of the same agate, which is fixed, as
of the cone f, and whereof the under surface is at the centre of suspension
and motion g for the conical pendulous weight f, f, whilst the upper surface of
the said agate is the centre of motion, and suspension k for the next pendulous
weight n; those two said centres of motion and suspension being one over the
other, and distant one from the other only as much as the thickness of the
agate. It is desirable that they should be near to one another in order that the
different pendulous weights may move as nearly as can be managed about a
common centre of motion or point of suspension, but the pendulous weights f,f,
and n, n, are free to move quite independently one of the other. The pen-
dulous weight n is a hollow tube or ring of lead, in order to admit the upright
pillar d through it; the said weight n is cut with a fine spiral screw thread
around its outer circumference to screw into a metal tube c, c, which has four
arms e, e, proceeding up from it to join to four places at the circumference of
the base of a thin cone of copper o, o, the vertex of which cone has the
before-mentioned point for the suspension of the pendulous weight n fixed
aforesaid, in the vertex

page_text: into it, that point being formed of hard bell metal, and from the upper side of
the same piece of bell metal another like point projects upwards to form the
centre point of motion and suspension m for the bowl F of the compass; the
said two points of the bell metal k (one projecting downwards and the other
upwards) being at as little distance one from the other as can be managed.
The bottom of the bowl F is a cone rising up within the interior of the bowl,
and at the vertex of the conical bottom is an agate m to rest on the above-
mentioned bell metal point k at the top of the thin cone o, o. The pendulous
weight His connected to the bowl F by two branches p, p, Figure 8, of a
forked piece shaped like the letter Y; those branches being joined at their
upper ends G, G, to the circumference of the bowl Fat two opposite places on
its circumference, and from thence the branches p, p, go down and unite
together beneath the bracket b (which forms the base of the upright pallar d),
and the weight II is fixed to the part where the branches p, p, unite, so that
it hangs down in the centre at the bottom of the box A, B, forming a long
pendulum to keep the bowl F horizontal and steady. The branches p, p, are
wide enough apart to admit the conical parts f, f, and o, o, of the pendulous
weights and n to move freely within the space between those branches with-
out touching, and so of the four arms e, c, of the weight n, they spread wide
enough apart to allow the concf to move freely within them without touching.
The angle of the cone f. f, is as much less than the angle of the cone o, o,
(and the angle of the latter is as
than the cone which forms the
bottom of the bowl F), as will leave each of the pendulums free to move
sufficiently far in any direction about its centre of suspension without coming
in contact one with another. The heavy cone f, f, forms a short pendulum,
the hollow weight n, n, a longer pendulum, and the pendulous weight II a
much longer pendulum than either of them. The operation of the two short
pendulums and n, of different lengths, whereby they enable the innermost
long pendulum H to retain the bowl F steady in a horizontal position, is the
same as already fully stated in respect to Sheet I., and therefore need not
be repeated. The upper part of the celestial compass, Sheet II., is somewhat
different in construction, but is essentially the same as that already described
in respect to Sheet I. The hour circle K is the same as in Sheet I., but it is
connected with the bowl F, and supported on two pivots fixed into the pro-
jecting ends G, G, of the branches p, p, which as before mentioned, are joined
to the circumference of the bowl. The arch of latitude or altitude L is a
complete semicircle, joined to the hour circle K at two opposite places in its
circumference, and descending therefrom beneath the bracket b, which forms the
base for the upright pillar d; the arch I. passes above the pendulous weight H.
much less
B

page_text: The clampt and slow motion screw for fastening the arch L and adjusting its
position, is at the end of a short arm, which is fastened to the circumference of
the bowl F, and projects out therefrom, and the vernier scale is borne by the same
arm. The hour circle K surrounds the bowl F (but without any interference
therewith), and it can be tilted up about its pivots at G, G, in order to give it
any required inclination to the horizon. Those pivots constitute a horizontal
axis of motion, and the arch Lis exactly concentre therewith. The upper circle
V, which is fitted upon the hour circle K, and turns round thereon, is the same
as in Sheet I., except that it is a mere ring which has no radial bar, but in lieu
thereof a semicircular bridge R is erected upon two opposite points of the
circumference of the ring V, so as to stand up in a plane at right angles to the
plane of the hour circle K. This bridge R reaches over the bowl F without
interference therewith in any position that is required to be given to the hour
circle or to the bridge R, which serves to support the telescope N, O, made
with a diagonal eye piece O, the same as in Sheet I. The telescope N, O,
is mounted on a short axis which is parallel to the plane of the hour circle K,
that axis being supported in two small bearing standards erected on the summit
of the bridge R. One of those standards is prolonged each way along the
bridge nearly as far as the length of the telescope, and is there formed into
two small arches M, M, carrying divisions for measuring the angles of
declination, and an index S is fixed fast on one end of the axis of the telescope
having a vernier scale engraved on each end of it for reading against the said
divisions. A clamp screw y is applied to the axis of the telescope to fasten it,
and that clamp has a slow-motion screw P to move the telescope slowly and
exactly to its intended declination. If the telescope is capable of moving
through an extent of about fifty degrees in declination, it will be sufficient for
observing the sun and moon at any season of the year, or any other celestial
objects within the zodiac. But note.-It will be advisable to have the telescope
made so as to be capable of moving at least sixty degrees in declination, as in
the case in Sheet I. The manner of adjusting and using the instrument,
Sheet II., is the same as in Sheet I., and requires no further explanation than has
been already given, excepting that in the instrument, Sheet II., the bowl F of
the compass and the measuring circles which it carries being wholly poised on
one centre point g, there is nothing to prevent them from turning round about
horizontally, or to retain them so as to keep the telescope pointing with cer-
tainty in any particular direction in respect to the box A, B, as the pivots of
the gimbals do in the instrument, Sheet I. Therefore, in making an observation
with the instrument, Sheet II., it will sometimes be necessary to push the bow!
F gently round about its centre of motion by application of a finger, until the

page_text: telescope is truly directed to the intended celestial object. The box A, B,
must be turned round about its upright axis C, so as to keep the bracket b far
out of the way of contact with the arch L, or with either of the branches p, p,
of the pendulous weight of the bowl F. Also, in order to make observation
of the local attraction of a ship by the instrument, Sheet II., the mark called
lubber's mark, which is made within the bowl F of the compass (as already
described in respect to Sheet I.), although the same will show the variation
of the magnetic needle, nevertheless that mark cannot have any decided
position in respect to the direction of the keel or length of the vessel, the
bearing of which in making observations on the local attraction of the
vessel must be attended to as well as in steering a ship. For this purpose,
the direction of the keel or bearing of the ship's head may be taken by another
ordinary steering compass, at the same time that the deflection or variation of
the magnetic needle in the celestial compass, Sheet II., is observed by means
of the divisions around its compass-card and its lubber's mark within its bowl
F, at that moment when the said mark has been directed to the true meridian
by some celestial observation made with the telescope of the instrument in
manner already explained. But in order to render the compass-card of the
celestial compass, Sheet II., available for determining the bearing of the ship's
head as well as the variation or deflection of that card from true bearings, a
mark to answer the purpose of an ordinary lubber's mark may be affixed to the
box or case A, B, when the same is fixed on the ship's deck in its proper position
in respect to the direction of her keel, that mark may be a straight horizontal
pointer directed in the direction of the ship's length towards the centre of the
compass-card so as to enable the observer to read which division on the card is
pointed to by the pointer. Or, an upright or two upright stems suitably dis-
posed may be used or may be combined with a horizontal pointer to direct the
eye of the observer for such purpose; or two such upright stems may by aid of
a lamp be made to cast their common shadow across the centre of the card for
such purpose. The mode of adjusting the horizontality of the bowl F of the
celestial compass, Sheet II., and the application of two or more spirit levels,
to its bowl F for verification of that adjustment every time that an observation
is made, may be the same as already described for the celestial compass,
Sheet I., and so of the mode of obtaining the true balance of all its several
moving parts, viz., its hour circle K, arch of altitude L, and declination
bridge R, and telescope N, O. Also the application of a refracting glass
wedge to the object glass of the telescope N for observing the pole star will
be the same as already described in respect to Sheet I. And respecting the
magnetic compass that is enclosed within the bowl F of the celestial compasses,

page_text: Sheet I. and Sheet II., the same may be constructed as usual in any other
kind of marine compasses with any kind of suspension and shape and size of
.needle that may be most approved, and with any suitable means of lifting up
the needle and card from resting on the point of suspension, in order to avoid
wearing the same when the card is not in use. And there may be a small and
very slender stop spring applied in the inside of the bowl F, with a small button
coming through to the outside, and which, on being touched by a finger, will bring
the said stop for an instant into gentle contact with the circular edge of the
compass card, and in order to check the vibrating motion thereof and cause
it to come the sooner to rest for making an observation, the said stop quitting
contact with the edge of the card the instant that the pressure of the finger
on the button is released, and the mark, termed the lubber's mark, may be
made upon the said stop. And note.-Respecting the suspension of the celestial
compass, Sheet I., by means of gimbal rings, the lines of direction of the
several pairs of suspending pivots which form the axes or horizontal centre
lines of motion, and which lines intersect each other at (or nearly at) a
common central point in the middle of the interior of the bowl, which point
is the common centre of the independant vibrating motions of all the several
pendulous weights f, f, and n, n, and of the bowl F of the compass, as herein-
before described. The directions of the said intersecting centre lines of
motion will (in my opinion) be most effective if they are disposed transversely
across the breadth and longitudinally along the length of the ship. But
nevertheless, I do not consider that circumstance to be essential, for the direc-
tion of the said intersecting lines may be disposed diagonally in respect to the
breadth and length of the ship. And as the box A, B, admits of being turned
round about on its axis C, I should recommend trials to be made, first, with
the direction of the said intersecting centre lines placed in conformity with
the breadth and length of the ship, and then placed diagonally thereto, in
order to find out in which direction the bowl will remain the most steady, for
it is probable that in some cases one of those directions, and in other cases
the other of those directions, may be most advantageous, and nothing but
experimental trial can determine which will be best in any particular case.
The telescope N, O, of the celestial compass (either Sheet I. or Sheet II.) is
furnished with cross wires in the focus of its eye glass, which wires intersect
each other in the centre of the field of view of the telescope, and serve to
direct the central line or line of collination of the telescope exactly to the
celestial object that is to be observed, all which is in the usual manner of
astronomical instruments, and requires no explanation; but for use at night, it is
necessary to illuminate those cross wires so much as to render them visible at

page_text: The shape of the said
The inside surface of
eye tube 0 over the
the same time when a star is viewed through the telescope; for this purpose,
a new sort of curved glass prism X (Figure 7, Sheet II., also Figure 9.) or
double wedge is applied over a lateral aperture in the tube of the eye piece O
in order to collect light from a lamp at one side, and direct the same through
the said aperture so as to shine upon the cross wires.
curved glass is shewn in the separate views, Figure 9.
the glass which applies against the outside of the
lateral aperture therein (as if it were a cover to that aperture) is hollowed
to a portion of a cylinder which corresponds exactly to the cylindrical
form of the tube against which it is applied. The middle portion w of the
external surface of the glass is also cylindrical and concentric to the cylin-
drical inside, the said cylindrical portion w forming the segment of a narrow
belt. The upper and lower portions of the external surface at v and a are
portions or segments of conical frustrums, whereof the bases commence at and
conform to the cylindrical belt w, and from thence taper away upwards
and downwards in a direction approaching towards the internal cylindrical
surface of the glass so as to terminate with a thin edge of glass at top and at
bottom. The said glass is retained in place against the outside of the eye tube
by a small rectangular border frame applied over and around the margin of
the glass, and fastened to the tube by small screws. The lateral aperture in
the tube () is rectangular and smaller in size than the glass, in order that the
external conical surfaces of the glass may collect light and transmit it by
refraction through the aperture into the interior of the eye piece and upon the
cross wires therein. Note.-This curved glass for illuminating the cross
wires in the eye piece of a telescope is equally applicable whether it is a
diagonal eye piece or a direct eye-piece.
In Sheet III. of the Drawings hereunto annexed, Figure 10 is a perspective
view, Figure 11 a horizonal plan, Figure 12 a side elevation, and Figure 13
an end elevation, of an instrument for measuring angles by reflection after the
mode of Hadley's sextant, but instead of refering those angles to the visible
horizon of the sea by directing the telescope A or line of sight to view that
horizon, the same is directed to view the pole star, and the plane of the
divided arch B, B, of the instrument (being at right angles to the direction of
the telescope A or line of sight), the said plane B, B, thereby becomes placed
parallel to the celestial equator or equinoctial; and any celestial object can, by
double reflection in the two plane mirrors I, D, (wherewith the instrument is
provided) be brought to apparent coincidence with the pole star as the same.
appears in the telescope; and then that celestial object will have the angles of:
its right ascension and declination indicated by readings upon the two divided.

page_text: arches B and M with which the instrument is provided for those purposes.
And, although the telescope A or line of sight of the instrument is directed to
view the pole star which is not at the true pole, the telescope will have its line
of collination or sight truly directed to the pole by aid of a transparent prism
or wedge of glass of the same kind as herein-before described in reference to
Sheet I., through which wedge the pole star is viewed, that wedge being fixed
upon a frame K at a opposite to and beyond the object glass d of the telescope
A; the two surfaces of that glass wedge a are plane surfaces, but are not
parellel, being inclined one to the other with a slight obliquity, in order that
the rays of light from the pole star in passing through the said glass wedge
may undergo a refraction which bends those rays just so much (viz., about an
angle of one and a half degrees,) as that the telescope A will become pointed
to the true pole when the pole star is seen through it, and the telescope
A being (as before stated,) at right angles to the plane of the divided arch
B, B, of the instrument, that plane will be parellel to the equinoctial or
celestial equator whenever the pole star is seen through the telescope and the
glass wedge a. The telescope A is fixed, as aforesaid, to the frame or plane G
of the instrument at some distance from the centre of the divided arch B, B,
and of its moveable radial arm or index H, the telescope A being situated at
the opposite side of that centre beyond or farther from the middle point or zero
of the divided arch B, B, that is, the zero of the divisions thereof.
A plane
mirror is fixed obliquely opposite to the object glass d of the telescope A
between the legs of the frame K, which frame is erected on the main frame G,
and which sustains the glass wedge a, before mentioned. The mirror I is
inclined at an angle of forty five degrees to the direction of the telescope A,
and also to the plane of the arch B, B; the under inclined surface of the
mirror being turned towards the centre of the arch B, B. One half of the
oblique mirror I is silvered, and the other half is plain transparent glass, the
same as the ordinary horizon glass of a Hadley's sextant; the silvered half of
the mirror I is nearest to the object glass d of the telescope A; but the
silvering is at the back surface of the glass, the front surface thereof being
turned towards the object glass of the telescope, and also towards the index
mirror D. The centre line of the telescope prolonged would pass obliquely
through the inclined mirror I at the place where the silvered and unsilvered
portions meet each other, and the diagonal obliquity of the mirror I adapts it
for receiving reflected rays of light from the index mirror D, and then directing
those rays by oblique reflection from the diagonal surface of the mirror I
down through the object glass d of the telescope A; and at the same time
the rays of light w from the pole star passing through the glass wedge a are

page_text: refracted thereby, as before mentioned, into the direction of the central line.
of the telescope, and the said rays pass obliquely through the thickness of the
unsilvered part of the oblique mirror I, and go down, but without alteration
of their direction through the object glass of the telescope at b, and along the
line of collination thereof to the eye of the observer. The divided arch B, B, and
the moveable radial arm or index II thereof, are the same as usual in Hadley's
sextant, except that the zero of the divisions is at the middle of the arch B, B,
and count each way therefrom; and when the index H is set to zero, as is
shewn in Figures 10 and 11, the direction of the index arm II, if it were
prolonged across beyond the centre of the arch B, B, would intersect the line
of collination of the telescope A. The index glass or mirror D is mounted
on the end 6 of the central axis of the instrument, and of its radial arm or
index H, as usual in Hadley's sextant, except that the front face or reflecting
surface of the mirror is not presented towards the arch B, B, but is turned
the contrary way, in order that the index mirror D may presents its reflecting
surface towards the half silvered inclined mirror I, and also the index mirror D
is attached to the central part of the radial bar or index H, by being mounted
upon pivots m, m, forming an axis which is parallel to the plane of the arch
B, B, and at right angles to the central axis of the instrument, whereon the
radial bar or index H is mounted. The said pivots m, m, of the mirror D
are received in suitable bearings at the upper ends of the prongs of a small
forked standard E, E, which is erected and fixed fast upon the end 6 of the
central axis, where that end comes up through the central part of the radial
arm or index H, and on the extremity of one of the pivots m (whercon
the index mirror is mounted) a small divided arm M is fixed, with a tangent
screw P acting in teeth around the circumference of the arch, to give it a
slow motion for the purpose of tilting or inclining the index mirror D either
way from its perpendicularity with the plane of the arch B, B. When the
index marks of the divided arch M is at zero of the divisions, then the plane
of the index mirror D is perpendicular to the plane of the arch B, B, but
when by turning the screw P the index mirror D is tilted or inclined either
way from that perpendicularity, then the divisions on the arch M indicate how
much it is inclined, and the divisions are numbered each way from the said.
zero so as to read double the angle that the index mirror D is actually
inclined from its said perpendicularity, in the same manner and for the same
reason that the divisions of the divided arch B, B, are numbered each way
from zero to read double the angle that the radial arm or index II is actually
moved about its centre. Note. When the said index H is at zero the axis
m, m, of the index mirror D will then be at right angles to the middle plane

page_text: which
passes through the central axis 6 of the instrument, and through the
central line of the telescope A. The small divided arch M is to measure the
declination of the celestial object which is observed by reflection of the ray
in the index mirror D; that ray being reflected from the reflecting surface
thereof, as at y, to the inclined surface of the other half silvered mirror I,
by which surface the ray is reflected down, as at 2, into the telescope A to the
eye of the observer. Hence at the same time he sees the pole star, as at w;
through the telescope A, and through the glass wedge a, and the refracted
image of the pole star is brought to coincide with the reflected image of the
other celestial object. The large divided arch B, B, with its moveable index II,
is to measure hour angles, and indicate the right ascension of the celestial
object that is observed, by reflection from the index mirror D, in manner
aforesaid, referring that angle to the hour circle (or particular meridian) in
which the pole star is situated; and in order that the zero of the divisions on
the large divided arch B, B, may be made to correspond to the beginning of
Aries (that being the zero from which right ascensions are reckoned), the glass
wedge at a is applied to the instrument by fixing it in a metal ring 7, such as
the object glass of a telescope is mounted in, and that ring 7 is mounted in an
annular socket or cell at the top of the fixed frame K, which, as before
mentioned, sustains the half silvered inclined mirror I between its legs, and in
that cell the glass wedge a can be turned round about the prolonged central
line of the telescope A as an axis of motion, by way of adjustment of the
position of the glass wedge a in respect to the before-mentioned middle plane
of the instrument, that is, the plane which passes through the centre line z of
the telescope A, and also through the central axis 6 of the divided arch B, B,
and which middle plane is at right angles to the plane of that divided arch.
And the said adjustment of the wedge a is such as that when the pole star
w is viewed through the telescope and wedge a, and the plane of the divided
arch B, B, is thereby brought parallel to the equinoctial (as before explained),
then the zero of the divisions of the arch B, B, will correspond to the beginning
of the sign Aries, in which state the instrument is prepared for measuring, by
the index H of that arch B, the right ascension of any celestial body which by
reflection from the index mirror D to the inclined mirror I, and then by second
reflection therefrom down into the telescope A, is brought with its said doubly
reflected image into apparent coincidence with the image of the pole star
refracted through the glass wedge a. The position of the glass wedge a must
for this purpose be such that the plane wherein the ray of light (which is bended
by refraction in passing through it) is situated will form an angle with the.
aforesaid middle plane of the instrument equal to the angle of right ascension

page_text: of the pole star, and the ring 9 of the glass wedge is fixed fast in its cell k by
a pin or screw when the position of the glass has been duly adjusted, as
aforesaid, and the instrument in that condition may be used in manner
following:-The whole instrument is held in the hand by its handle W in the
manner of holding a sextant, and the telescope A (which has cross wires in
its cyc piece) is directed to the pole star w, in which state the plane of
the arch B will become parallel to the equinoctial, then for any celestial
object which is to be observed (suppose, for instance, one of the planets,)
accordingly as its right ascension is east or west of the commencement of the
sign Aries, so the index H of the divided arch B, B, must be moved to one
side or other of the zero of its divisions until the vernier of the index H reads
an angle somewhat near to that of the expected right ascension of the planet;
and also according as the declination of the same planet is north or south of
the equinoctial, so the index mirror D must be tilted or inclined one way or
other in respect to the plane of the arch B, B, which is done by turning the
tangent screw P until the index marks for the divisions on the arch M reads
an angle somewhat near to that of the expected declination of the planet.
The instrument being thus prepared and the telescope A directed to view the
pole star, the doubly reflected image of the planet will most probably be
visible within the field of view of the telescope at the same time with the
refracted image of the pole star, and by moving the index H by its slow motion
serew, and the arch M by its tangent screw P, according as each may require
to be moved, the said doubly reflected image of the planet may be brought
to apparent coincidence with the refracted image of the pole star, that
coincidence taking place in the field of view of the telescope A at the inter-
section of the cross wires in its eye piece, and then the observation being
completed the amount of right ascension of the planet may be read off from
the vernier r of the index II, and the amount of its declination at s on the
divisions of the arch M. The dotted lines in the perspective view, Figure 10,
will serve to explain the course of the rays in such case, although those dotted
lines actually represent a different case, a being supposed to be the ray coming
downwards from the celestial object (which, in the above case, was stated to be
a planet,) to the central part of the index mirror D is then reflected from the
inclined surface of that mirror in a direction y, parallel to the plane of the
arch B, B, and along the before-mentioned middle plane of the instrument
until the reflected ray y strikes the middle part of the under surface of the
inclined mirror I at the junction of the silvered and unsilvered parts thereof,
and from that under surface the ray is turned down by a second reflection into,
the direction, which is the line of collination of the telescope A, and which is

page_text: at right angles to the plane of the arch B, B, and is also in the aforesaid middle
plane of the instrument; likewise the dotted line w is supposed to be the ray
from the pole star coming downwards to the glass wedge a, and by the refractive
power thereof the ray w, after passing through that glass wedge, becomes bended
down into the aforesaid direction,, and then passes without change of that
direction obliquely through the transparent part of the inclined mirror 1 down into
the telescope A, along the line of collination thereof, so that the refracted ray
w,, from the pole star coincides with the doubly refracted ray x, y, z, from the
celestial object. Note.-In the Drawing the vernier 7 of the index II being repre-
sented at zero of the divisions on the arch B, B, the celestial object whose ray x
would be reflected to y and, as aforesaid, would be at nothing in right ascen-
sion, that is, it would be in the same hour angle with the commencement of
Aries, or would come to the meridian at the same instant therewith. The said
celestial object being so situated requires the middle plane of the instrument
to be directed to it, but it will be easy to understand that, if the said object
were situated either to the right or to the left of that position, the index
mirror D might be turned to either side as would be required, by moving its
index Hin order to receive the ray, such as a, coming sideways from the said
object, and reflect that ray from the inclined surface of the mirror into the
same direction y, as aforesaid, which direction of the ray, after reflection
from the index mirror D, is in all cases the same, viz., in the middle plane of
the instrument, and parallel to the plane of its arch B, B, and at the same
distance from or above that plane, as the axis m, m, of the index mirror D is
situated, and the vernier r of the index H, well read on the divisions of the
arch B, B, the amount of right ascension of the same celestial object. And
note also, in the Drawing the index mirror D and the divided arch M is repre-
sented as so greatly inclined upwards that it could not then reflect the ray
from any planet in the manner formerly stated, and therefore to correspond to
that statement it must be supposed that the tangent screw P is turned until
the index mirror D is tilted down so much from the position represented in
the Drawing that the arch M will read at s, a degree of declination suitable
for a planet. The Drawings represent the instrument in a state which can
never be required for use except for the purpose of adjustment, viz., when it is
úsed to observe the pole star both by double reflection in the two mirrors D, I,
and by refraction through the glass wedge a at the same time; that is to say,
the telescope A being directed to the pole star the ray w therefrom will be
bended to the direction in the manner already explained. The vernier r of
the index II being set to read on the arch B, the right ascension of the pole
star and the divided arch M to read at s the declination of the pole star,

page_text: then the ray x, y, z, also proceeding from the pole star, will cause the
doubly reflected image of the pole star to appear to coincide with that other
image of the same star which is seen in the direction w,, through the tele-
scope A and the glass wedge a, the coincidence of those images taking place
in the centre of the field of view of the telescope at the intersection of the
cross wires in its eye piece. And if the said two images of the pole star do.
not so coincide, the instrument will be known to be out of true adjustment
and must be rectified accordingly. Note.-The divisions on the small arch
M for declination may be subdivided by a vernier scale at s, or else the
tangent screw P may have a divided micrometer head n for the purpose of
such subdivision. And note.-The instrument may be adapted to any other
circumpolar star instead of the pole star, having another glass wedge which is
formed to have as much more refractive power as will just suit the polar dis-
tance of the said other circumpolar star, and that other glass wedge with
its ring like q being substituted for the one herein-before described in the
cell k of the frame K; the said glass and ring must be turned round about in
the said cell k, to suit the right ascension of the said circumpolar star, and
then made fast in the cell by a pin or screw. In this way the instrument may
be provided with several glass wedges adapted to various stars, which will Le
most suitable to be used in turn for making observations either in the southern
hemisphere of the earth, or in the tropical regions, or in the northern hemi-
sphere thereof. The instrument may likewise have an additional inclined
mirror, mounted in a suitable frame, which is applied in the cell k at the top
of the frame K, beneath the glass wedge a, for the purpose of receiving a ray
laterally from some other star having a very considerable polar distance, and
for reflecting that ray down into the direction of the line of collination of the
telescope A, at the same time that the pole star (or other circumpolar star) is
viewed through the telescope and through the diagonal mirror I, also through
the said additional inclined mirror, and through the glass wedge a before men-
tioned. The two images produced from the said rays of both the said stars
being brought to coincidence in the field of view of the telescope, and at the
intersection of the cross wires therein, by way of determining the position of
the instrument with great certainty, and the image of the celestial object (a
planet, for instance,) whereof the right ascension and declination is to be
observed, may be brought by double reflection (in the two mirrors D and I)
of a ray such as x, y, z, to a common coincidence with the aforesaid two
coinciding images at the intersection of the cross wires of the telescope,
so that three images will be brought to coincidence, whereof two are, as
before mentioned, for giving the instrument a true position, and the third for

page_text: not.
.
surface of the mirror
ascertaining (by the readings of the divisions of the instrument at r and s), the
right ascension and declination of the object from which the third image is
formed by the double reflection a, y, ; such an additional inclined mirror may
be fixed obliquely across a hollow circular box Z, Figure 14, which is adapted
to fit into the cell at the top of the frame K in place of the ring 7 of the
glass wedge a, which ring is placed in a cell at the top of the box Z,
Figure 14, and fits exactly therein the same as it would do into the cell k, so
that the glass wedge a becomes mounted above the inclined mirror of the
box Z. The box Z has an aperture at one side to admit a ray laterally from
the star to the mirror 7. That mirror is a plane glass plate of uniform
thickness, and may be half silvered in the manner of the diagonal mirror I or
The obliquity wherewith it is placed in its box Z, must be suitable to
the declination of the particular star which is to be reflected by it, so that the
reflected ray from its under surface may be reflected by the under inclined
exactly down the line of collination of the telescope
A. The inclined mirror being held fast in place in the circular box Z by
suitable setting screws, they will enable its inclined position to be regulated
with precision to suit the said declination. And the box Z containing the
inclined mirror 1, is turned round in its cell until the angle which the
inclined mirror makes with the aforesaid middle plane of the instrument
will exactly suit the right ascension of the said particular star, which is to be
reflected by it, and there the box Z is fixed in its cell k, by a pin or screw. And
the ring of the glass wedge a is adjusted into its cell g at the top of the
box Z in the same manner as it would be adjusted in the cell k, as before
explained, in order in either case to suit the right ascension of the pole star (or
other circumpolar star, to the polar distance of which the refractive power of
the glass wedge a is adapted), and when so adjusted the ring 9 of the glass
wedge is made fast in its said cell g by a pin or screw. The ray from that
star, after passing through the glass wedge a, and being refracted thereby
into the direction of the line of collination of the telescope A must pass
obliquely through the glass of the inclined mirror 1, and then in like manner
obliquely through the glass of the diagonal mirror I before reaching the object
glass d of the telescope A, but the direction of the ray is not altered by so
passing obliquely through the glass of those two mirrors, because both those
glasses are plates of parellel thickness. And further, the cell k at the top of
the frame Khas divisions around its outer circumference, as shewn at j.
which divisions represent and are numbered with the twenty-four hours of the
day, and either the ring 7 of the glass wedge a, or else the circular box Z,
Figure 14, of the additional inclined mirror (whichever of those may be

page_text: fitted into the cell ), instead of being held fast in one invariable position in
that cell by pin or screw, as before-mentioned, the same may be adapted to
turn round in the cell k with an index mark or vernier f, to denote how
many hours divisions the glass wedge (or, the additional inclined mirror 7,
Figure 14, together with the glass wedge,) have been turned round in the cell
k. With this provision the instrument is adapted for measuring the meridian
distance of a celestial object by taking a similar observation thereof with the
instrument to that already described for measuring the right ascension. The
index mark or vernier f, which applies to the said divisions of twenty-four
hours at j, around the cell, is so adjusted that being set to the time of day
when an observation is about to be made, reckoning by syderial time), and
the telescope being directed to the pole star (or other circumpolar star, as the
case may be), and an observation made by double reflection of a celestial
object (a planet, for instance,) in the two mirrors D and I bringing the reflected
image of that object to apparent coincidence with the refracted image of the
pole star, then the aforesaid middle plane of the instrument will be in the
meridian, and the reading of the vernier r on the divisions of the arch B, B,
will be meridian distance instead of right ascension, as in the case formerly
described. And note.-The eye piece of the telescope A may have a curved
glass prism or double wedge applied to it in the manner shewn at X, v, w, x,
Figure 9, Sheet II., and herein-before described for the purpose of trans-
mitting light to illuminate the cross wires. In its eye piece R are darkened
glasses for making observations of the sun; they are the same as usually
applied to sextants, and can be turned up one, two, or three at a time to
intercept the ray y which is passing from one mirror D to the other I, or they
can all three be turned down out of the way; and S are other darkened
glasses applied at the top of the frame K beneath the cell k, so that they can
be turned one or two to intercept the ray passing down to the telescope A, or
can both be turned out of the way. A dark glass may be screwed on over
the eye hole of the telescope A. The diagonal mirror I is fixed between the
legs of the frame K by screws which admit of adjusting its position to a
proper inclination of exactly forty-five degrees. And note.--The part G of
the frame, and the several arms T of the arch B, B, of the instrument, may
be made curving downwards to join with the central socket from which those
arms and frame G radiate; but that central socket, and the outer extremities
of the arms T and part G, to which the arch B, B, and frame K, K, is
affixed, being still in the same positions as represented in the Drawing, then
there would be room for the arch M of declination to be of a much larger
radius than is represented, because its lower part might descend down into

page_text: the plane of the arch B, B, where the arms T and the part G now are, and
by being larger the divisions of the arch M would be more accurate.
And whereas, Letters Patent were granted to me, George Graydon, by
His late Majesty King George the Fourth, on or about the Fifth day of
August, One thousand eight hundred and twenty-four, for a new compass for
navigation and other purposes, which compass had been then newly invented
by me, and in my Specification which I caused to be duly inrolled in the
High Court of Chancery, in compliance with a proviso contained in the said
Letters Patent, I did describe three instruments, which I then denominated
the celestial compass, and such instruments, with various improvements on
the constructions therein described, have been made and used under authority
of the said Letters Patent; and whereas, such celestial compasses have
been intended for attaining the same objects as the instruments herein-before
described, and have in part attained such objects, I wish to be understood
that I make no claim under or by authority of the Letters Patent now lately
granted to me by Her present Majesty as aforesaid, to the exclusive use of
any of the instruments described in my said former Specification, or made
and used under authority of the said former Letters Patent; but I only claim
an exclusive right to the new improvements which I have now recently made
on those former instruments, and instruments constructed according to and
containing those new improvements have been herein-before described; and
whereas, in all my said former celestial compasses there was contained, as
essential parts thereof, an hour circle capable of being elevated by aid of an
arch of latitude or altitude, in order to incline the plane of such hour circle so
much from the horizontal as to place it parallel to the equinoctial or equator,
and with a moveable upper part applied upon such hour circle, and turning
round about the same in a suitable manner for measuring the hororary angles
described by celestial bodies or their meridian distances, together with other
moveable parts applied upon the before-mentioned upper moveable part, for
the purpose of measuring the angles of declination of such celestial bodies or
their distances above or below the equinoctial; and the said parts, suitably
combined one with another for observing such angles, were mounted in one
gimbal ring, so as to be wholly suspended upon pivots disposed in two lines of
direction crossing each other at right angles, in order to allow of free motion
in every direction, and with one heavy pendulous weight affixed at the very
lowest situation in the combination of suspended parts, and at a sufficient
distance below the level of the said suspension pivots to enable the gravitation
of such weight to place the whole combination of suspended parts in the true
intended position in respect to the horizon, as well as to retain them in such

page_text: position whilst the required celestial observations were made. And although
that simple mode of suspension, by means of one gimbal ring with one pendu-
lous weight, will completely answer the purpose when such an instrument is
used on shore, and will also enable it to give very useful results when used on
board ships at times when there is but little motion thereof; nevertheless, the
tendency of such instruments to remain steady is not sufficient to enable them
to be used at sea under circumstances of agitation and motion of the ship
when it would be highly, desirable to do so, and when by aid of my present
improvements useful observations may be taken with the instruments herein-
before described, which are constructed according to those improvements.
Having now described the said instruments constructed according to and
containing my new improvements, I, the said George Graydon, do hereby
declare that the new Invention, whereof the exclusive use is granted to me by.
the said Letters Patent, consists in the following particulars:-
First, in the mode herein-before described in reference to Sheet I. of the
Drawings hereunto annexed, whereby the compass bowl F, carrying the
measuring circles of the celestial compass, is suspended on pivots forming
intersecting centre lines of motion within a series of gimbal rings, which are
arranged and suspended one within another with two or more independant
pendulous weights, as f and n, applied to certain of those rings, so as to be
suspended by means of the pivots thereof, with free liberty of independant
motion about all those pivots, as about one common centre of motion, and in
any direction about the same, the said pendulous weights, as f and n, being at a
sufficient distance below the level of that said common centre of motion to give
each of the suspended parts to which the said several pendulous weights are
applied an adequate tendency to remain in a quiescent position by the gravi-
tation of such weights, but the several pendulous weights f and n are cach at
liberty to move one quite independantly of another. And further, the outer-
most of those pendulous weights, as f, which derives its whole support (by
intervention of an exterior gimbal ring a, with pivots forming intersecting
centre lines of motion) from the external box or case A, B, of the instrument,
has the centre of gravity of its weight f nearer to the level of the aforesaid
common centre of motion than the next pendulous weight n, which latter
derives its whole support (by intervention of another smaller gimbal ring k
with pivots forming intersecting centre lines of motion) from parts belonging to
the aforesaid outermost pendulous weight f, in order that the pendulous weight
n may not receive any tendency to motion from the external box or case A, B,
beyond so much motion as the said outermost pendulous weight may bave
received therefrom, and can transmit to the next pendulous weight n. And the

page_text: compass bowl F, with a still lower innermost pendulous weight H of its own,
having the measuring circles of the celestial compass applied upon and around it,
derives its whole support (by intervention of an innermost gimbal ring m with
pivots forming intersecting centre lines of motion) from parts belonging to the
pendulous weight n. The bowl F having the centre of gravity of its innermost
pendulous weight H much lower down below the common centre of motion
than the other pendulous weights f and n are, the bowl is the more disposed to
quiescence by the gravitation of that weight II, and the bowl F having no
direct connection with the external box or case A, B, cannot receive any ten-
dency to motion therefrom, except inasmuch as the outermost pendulous weight
fmay have derived some small motion therefrom, and as the next pendulous
weight n (from which the bowl F obtains its whole support) may have derived
a still less motion from the outermost pendulous weight f, wherefore it is only
inasmuch as the bowl may be influenced by the small extent of motion of the
pendulous weight n that it will receive any tendency to motion, and owing to
the greater length of the pendulum H of the bowl than of the pendulum
formed by the weight n, the former II is not disposed to accompany the latter
n in the oscillatory motion which that latter n may have acquired from the
outermost pendulous weight f. And in like manner and for the same reason,
the pendulous weight n is made so as to form a longer pendulum than the pen-
dulum that is formed by the outermost weight f, in order that the former n will
not be disposed to accompany the latter f in the oscillatory motions which
that latter may have derived from the external box or case A, B. And
whereas in my former celestial compasses there was a pendulous weight
answering to that one I which is affixed to the bowl, and the same obtained
its support (by intervention of a gimbal ring answering to that marked a, a,
with pivots forming intersecting centre lines of motion) from an external box
or case answering to that marked A, B, therefore I make no claim under the
present Letters Patent to the one pendulous weight, such as H, suspended in
the external box, or case A, B, by intervention of only one gimbal ring, such as
a, a. But this first article of my present improvements is on that simple mode
of suspension, and consists in the additional application (in the manner herein-
before set forth) of two or more additional pendulous weights, such as n and f,
with intervening gimbal suspensions, such as k, k, and m, m, to allow liberty
of motion in all directions, that additional application being made between the
one innermost pendulous weight H and the one outermost gimbal suspension a,
the said additional pendulous weight being adapted to form independant pen-
dulums of very different lengths from that formed by the innermost pendulous
weight H, and also of different lengths from each other in the manner and

page_text: for the reasons herein-before set forth. And all the several parts of the
celestial compass, Sheet I., being suitably combined one with another in the
mauner and for the purposes herein-before explained, the whole constitutes a
new combination, which is a great improvement upon the former celestial
compasses. And note.-Although I have mentioned only two additional
pendulous weights f and n, I do not confine myself to that number, for three,
four, or more pendulous weights may be introduced one within another with
suitable intervening gimbal suspensions if it is desirable to obtain still more
steadiness than will be given by two such additional pendulous weights as
berein-before described in reference to the Drawing, Sheet I.
Secondly, in the mode herein-before described in reference to Sheet II.,
whereby the compass bowl F, carrying the measuring circles of the celestial
compass, and having a long pendulum descending from the bowl F,
is wholly supported or freely poised on the point of one central pivot at m,
so as to be capable of free motion in all directions about that point m by
the gravitation of the pendulum H, and which pivot m is at the summit
or vertex of another second pendulum n, n, c, c, e, e, o, o, that is itself
supported or poised upon the point of one central pivot which belongs
to it, whereby that said second pendulum is capable of free motion in all
directions about that point k by the gravitation of its weight n, n, and the
said last-mentioned point k is supported in an agate cup at the summit or
vertex of another pendulum ff, which is itself poised on the fixed point g at top
of a central upright pillar d, which is affixed by a bracket b to the box or case
A, B, wherein the whole instrument is enclosed, the last-mentioned pendulum
ff, being capable of free motion in all directions about that fixed point g, by
the gravitation of its weight f, f, but having, in consequence of that weight, a
tendency to hang quiet will only partake of part of the motion of the external
box or case A, B, and the agate cup on the top of the said pendulum being
the sole support for the suspension point of the second pendulum n, n, c, c,
e, e, o, o, the lower pendulum having its own tendency to hang quiet, will only
partake in part of the motion of the pendulum f, f, wherefore the bowl F
of the compass being wholly supported upon the central point m at the vertex
of the said second pendulum n, n, c, c, e, e, o, o, will have but a very slight
impulse or tendency to motion communicated to it, and owing to the length of
its pendulum H, giving that pendulum a great tendency to hang quiet, it will
be likely to do so and keep the bowl F, together with the measuring circles,
which are supported thereby, sufficiently steady in a horizontal position proper
for taking observations. And note. Whereas compasses called azimuth

page_text: compasses have been heretofore made with the bowl containing the magnetic
needle suspended by poising a central socket formed at the interior hollow
bottom of the bowl upon a fixed point at top of an upright pillar with liberty
of free motion in all directions about that fixed point, such mode of suspension
being a substitute for gimball suspension; wherefore I make no claim to such
mode of suspension for the bowl of the celestial compass, if the same be
performed by merely poising the bowl F upon one fixed point, such as g, with
one pendulous weight affixed to the bowl answering to H, but this second
article of my present improvements is an improvement on that simple mode of
suspension, and consists in the additional application in manner herein-before
set forth of two or more pendulous weights, such as n and f, poised on points
of suspension, one upon the other, with liberty of motion in all directions about
those centres, and all those suspensions intervening between the suspension of
the bowl itself and the fixed supporting point g, which sustains the whole
weight. The said additional pendulous weights being adapted to form
independent pendulums of very different lengths from that formed by the
pendulous weight H of the bowl itself and also of different lengths one from
another; in the manner and for the reasons herein-before set forth. And all
the several parts of the celestial compass, Sheet II. being suitably combined
one with another, in the manner and for the purposes herein-before explained,
constitutes a new combination which is a great improvement upon former
modes of suspending celestial compasses. And note. Although I have
mentioned two additional pendulous weights f and n, I do not confine myself
to that number, for three, four, or more pendulous weights, or independant
pendulums may be introduced one within another and poised independantly
one of another on centrepoints resting one upon another if it is desirable
to obtain greater steadiness than will be given by two such pendulous weights
as f and n.
Thirdly, in the mode herein-before described, in reference to Sheet I. and
Sheet II., of applying a glass prism or refracting wedge to the telescope of a
celestial compass, for the purpose of observing the pole star or some other
circumpolar star, for the polar distance of which star the refraction of
such wedge is adapted, and thereby obtaining the altitude of the true
pole, although the star which is viewed through the telescope and the
said glass wedge is situated at some angular distance from that true
pole.
Fourthly, in the mode herein-before described in reference to X, v, w, x,
Sheet II., Figure 9 (and also in reference to Sheet I.), for transmitting light

page_text: transversely through a bended glass prism into the eye piece of the telescope
in order to illuminate the cross wires therein sufficiently to render them visible
to the observer.
Fifthly, in the mode herein before described in reference to Sheet III., of
constructing an instrument for measuring the angles that are subtended in the
heavens by celestial bodies, with the telescope or line of sight disposed at right
angles to the plane of the divided arch or circle of the instrument, and with a
refracting glass prism or wedge applied to the telescope or line of sight in such
mauner as that the pole star (or other circumpolar star to the polar distance,
whereof the refracting power of the said wedge is adapted) being received through
the telescope or line of sight, and through the glass wedge, then the telescope
or line of sight will become directed to the true pole, and consequently the plane
of the divided arch or circle of the instrument will become parallel to the
equinoctial, in which position observations may be made of the right ascension
and declination of any celestial object by means of the mirrors of the instruments
bringing the reflected image of such object into apparent coincidence with
the pole star (or other circumpolar star,) which is at the same time viewed
through the telescope or line of sight of the instrument, and through the
refraction of the glass wedge; also, in applying the said glass wedge to
the telescope or line of sight in manner herein-before described, so that the
said wedge can be turned round about the line of collination or of sight, as an
axis, in order to suit the time of the day or night when an observation is about
to be made, and thereby to obtain the meridian distance and declination of the
celestial object which is observed at such time; also, in applying a half-
silvered plane reflecting mirror obliquely to the telescope or line of sight in
conjunction with the said glass wedge, in order to obtain the reflected image of
some well-identified circumpolar star to the polar distance and right ascension,
whereof the said reflecting mirror is adapted by its obliquity to the line of
collination or sight, and by its position in respect to other parts of the instru-
ment in such manner that the said reflected image of the said circumpolar star
may be brought to apparent coincidence with the pole star (or other star),
which is at the same time viewed through the telescope or line of sight, and
through the refraction of the glass wedge, and the two apparently coincident
stars may also be brought to apparent coincidence with the reflected image of
the celestial object whereof the right ascension and declination is to be observed
by the instrument in order that, by such apparent tripple coincidence of the
celestial objects at the same time in one view, the right ascension and declina-
tion of one of those objects may be measured and determined by the instrument
which refers the same to the known right ascension and declination of the other

page_text: two objects. All the several parts of the said instrument, Sheet III., being
suitably combined one with another, in manner and for the purposes herein.
before explained, the whole constitutes a new combination, which is a great
improvement upon any reflecting instruments heretofore invented for observing
the right ascensions and declinations, or the meridian distances and declina-
tions of celestial objects. And whereas, in my said former Specification an
instrument or celestial compass was described for observing meridian distances
and declinations of a celestial object by reflection, & bringing the reflected
image of such object to apparent coincidence with the reflected image of the
pole star.
I do not now make claim under my present Letters Patent to any part of
the said former instrument or celestial compass, but I confine my present claim
of Invention in respect to the instrument herein-before described in reference
to Sheet III. to the particulars above stated under the fifth article of my
present improvements.
In witness whereof, I, the said George Graydon, bave hereunto set my
hand and seal, this Second day of November, One thousand eight
hundred and thirty-nine.