AN IMPROVED INSTRUMENT FOR THE MEASUREMENT OF ANGLES
Year: 1839

page_text: TO ALL TO WHOM THESE PRESENTS SHALL COME, I, FREDERICK
AUGUSTUS GLOVER, of Charlton, near Dover, in the County of Kent, Clerk,
send greeting.
WHEREAS I did, by petition, humbly represent unto Her present most
Excellent Majesty Queen Victoria, that, after much study and expense, I had
invented "AN IMPROVED INSTRUMENT FOR THE MEASUREMENT OF ANGLES," and
Her said Majesty being willing to give encouragement to all arts and inven-
tions which may be for the public good, was graciously pleased, by Her Royal
Letters Patent under the Great Seal of Great Britain, bearing date at
Westminster, the Second day of November, in the third year of Her reign,
for Herself, Her heirs and successors, to give and grant unto me, the said
Frederick Augustus Glover, my exors, adññors, 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 I or they should agree with (and no others), from time to time and at all
times during the term of years therein expressed, should and lawfully might
make, use, exercise, and vend my said Invention within that part of Her said
Majesty's United Kingdom of Great Britain and Ireland called England, Her
Dominion of Wales, and Town of Berwick-upon-Tweed, and also in all Her
Majesty's Colonies and Plantations abroad, in such manner as to me, my
exors, adñiors, and assigns, shall seem meet, and that I or they shall enjoy
the whole profit and advantage arising by reason of the said Invention during
the said term of years therein mentioned; and for that end Her said Majesty
for Herself, Her heirs and successors, requires and strictly commands all Her
subjects whatsoever, within England, Wales, and Town of Berwick-upon-
Tweed, and also in all Her Colonies and Plantations abroad aforesaid, that
they shall not, during the continuance of the term of years thereby granted,

page_text: either directly or indirectly make, use, or put in practice my said Invention,
or any part thereof, or in anywise counterfeit, imitate, or resemble the same,
nor make or cause to be made any addition thereunto or subtraction there-
from whereby to pretend himself or themselves the inventor or inventors
thereof, without the license of me, the said Frederick Augustus Glover, my
exors, admors, or assigns, in writing first had and obtained in that behalf.
And whereas the said Letters Patent contain a proviso, obliging me, the said
Frederick Augustus Glover, particularly to describe and ascertain the nature
of my said Invention, 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
inrolled 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 bad) will more fully and at large appear.
NOW KNOW YE, that in compliance with the said proviso, I, the said
Frederick Augustus Glover, do hereby declare that my said Invention is
described and ascertained in manner following, and by and of the Drawing
hereunto annexed, that is to say:-
My said improved instrument for the measurement of angles is intended to
effect all the same purposes as the instruments now in use for measuring
angles, called Hadley's reflecting quadrant or reflecting sextant, the pocket or
box sextant, Sir Howard Douglas's reflecting semicircle, and others of the like
kind, in all of which instruments one of the objects which is observed is viewed
by two successive reflections in two plane mirrors wherewith such instruments
are always provided, but in my said improved instrument only one such mirror
is used, and only one reflection of the object takes place. And whereas in the
ordinary Hadley's quadrant or sextant, in order to use the same for measuring
the altitude of the sun, or of any other object above the horizon, either a
horizontal reflecting surface called an artificial horizon must be used, or else a
view of the horizon of the sea is requisite, as an artificial horizon cannot be
used at sea at all, and as the horizon of the sea cannot always be seen in hazy
weather, and very rarely at night, the instrument becomes useless in such
cases; but my said improved instrument is provided with a gravitating pendulum
carrying a horizontal line of sight, and governing that line so that it will
preserve a truly horizontal direction, in order that the altitude of an object
which is viewed by only one reflection in the one mirror of the instrument
may be measured by reflection to the said horizontal line of sight without any
necessity for a view of the horizon of the sea.
Figure 1 of the Drawing hereunto annexed is a full-size representation of
one form of my said improved instrument adapted for the use of seamen, in

page_text: place of the Hadley's quadrant or sextant commonly used by them. A is the
telescope, to which the eye of the observer is applied; B, B, is the divided
arch, which is one-fourth of the whole circle; H is the index affixed to the
projecting end of an axis which occupies the centre of the arch B; and on the
central part of the index H a plane or flat reflecting mirror D is fixed with
the plane of its reflecting surface exactly coincident with the central line of the
said axis, if the said line were prolonged, and a fine line is scratched along the
surface of the said mirror, forming a continuation or prolongation of the said
central line of the axis of motion. The plane of the said mirror D being
supposed to be extended towards the arch B, corresponds with the edge or
radial line h of the index II, which index has a vernier scale upon the end of
it at r to apply to and subdivide the divisions on the arch B. And note.-
Those divisions are numbered so as to indicate only half the angle that the
index H is moved over from its zero or point of commencement, in the same
manner as is usual in Hadley's quadrant or sextant.
The instrument when used for the measurement of angles of altitude is held
in the hand by its handlo W, with the telescope A directed horizontally in the
same manner as Hadley's quadrant or sextant, but the line of sight through
the telescope in my improved instrument is directed to the surface of the index
mirror D so as to view the line scratched thereon, as aforesaid. And assuming
(for the present) that the line of sight y, y, of the telescope A is kept in a
truly horizontal direction, then the instrument will measure the angle of
altitude of any object whereof a ray (as æ, for instance) coming upon the
surface of the mirror D at the said line which is scratched thereon; the said
raya is reflected from that surface into the line of sight y of the telescope A.
for then the angle of the altitude of the said object above the horizontal line of
sight y, y, through the telescope A will be indicated by the vernier r of the
index H, and the divisions on the arch B to which that vernier applies. And
as to the pendulum and horizontal line of sight, which pendulum, as before
> mentioned, retains that line of sight in a horizontal position by the gravitation
of the pendulum, that pendulum is enclosed within a hollow box of thin
metal I, which is affixed to one of the radial bars T of the divided arch B, so
that the plane of the box is parallel to the plane of the arch, but so far within
that plane as will allow the index H to move across before the front side of the
box I without touching. The pendulum itself is suspended within the box,
as is represented by dotted lines K in Figure 1; and Figures 2 and 3 are a
front and side view of the box I with the pendulum K within it.
The
pendulum is suspended upon fine pivots a, a, at the opposite sides of the short
cylindrical tube Y. which tube contains the aforesaid line of sight, the pen-

page_text: dulum being affixed to the under side of the tube Y by one end of its
stem l, m, which extends horizontally to reach into the hollow of the box I and
then turns down therein with a straight stem m, in order to suspend the bob
or weight K at the lower end of the stemil, m. The pivots a, a, are mounted
in a supporting cock E, which is affixed to the upper radial bar T of the
arch B, B, and projects out therefrom, but rising up with an arch so as to
leave room for the cylindrical tube Y to move freely without touching the arch.
The hollow box I is affixed to a perpendicular branch of the cock E, which
branch reaches downwards behind the back of the box for that purpose. The
cock E is fixed on the radial bar T with a notch clipping over the bar T, from
which it can be easily removed, together with the bar I, pendulum K, and line
of sight tube Y, if required; but when in place the cock E can be fixed fast
by 1 pin passing through both prongs of the clipping part and the bar T.
The weight of the pendulum K when it hangs freely and at rest in its box I
causes the line of sight tube Y to assume and to retain a truly horizontal
direction, and the position of the stem m of the pendulum in respect to the
tube is adjusted by suitable setting screws 1, 1, so that the line of sight
through the tube Y will be exactly horizontal when the pendulum K hangs
freely vertical.
The line of sight tube Y might have cross wires in the aperture at each
end of it to indicate the intended line of sight through the central axis of
the tube Y, but what I prefer is to apply plane or flat glass of uniform
thickness in each aperture, with cross lines drawn on each glass, so as to
divide the circular field of view into four quadrants; and the two opposite
quadrants of each glass are darkened, whilst the other two opposite quadrants
are left transparent glass, to see through clearly. This is shewn at Figure 4,
wherein 1, 2, 3, 4, are the four quadrants of the glass P, at one end of the
tube Y, and 5, 6, 7, 8, are the corresponding four quadrants of the glass Qat
the opposite end of the tube Y. The intended line of sight. is formed by
looking beneath the under side of the darkened quadrant 1 in one glass P,
and over the upper side of the darkened quadrant 5 of the other glass Q,
that is, for one half or side of the field of view, videlicet, the left-hand side;
but for the other half or right-hand side thereof the sight is directed by looking
over the upper side of the darkened quadrant 3 of one glass P, and beneath
the under side of the darkened quadrant 7 of the other glass Q. The two
glasses P and Q are turned round in their respective cells at each end of the
tube Yuntil the several radial lines by which each glass is divided into
quadrants, as aforesaid, are placed exactly in horizontal and vertical directions,
and then the several quadrants at each end of the tube Y will correspond, and

page_text: the horizontal sides of the darkened quadrants will form a true line of sight,
as aforesaid, through the central axis of the tube Y, and it will be known when
the vision is truly directed in that line of sight by the appearance of a fine
continuous line of bright light, extending horizontally across the field of view,
like a bright wire, when the sun or moon or other brilliant object is viewed
through the tube Y, the line being equally fine and distinct at each end of it;
for if the vision is directed in the slightest degree too low for the intended
horizontal line of sight, then the said horizontal bright line across the
left hand and half of the width of the field of view will appear broad
and coarse at the same time that the intended continuance of the said
line across the other or right-hand half of the said width will disappear
altogether. Or, on the other hand, if the vision is directed in the slightest
degree too high for the intended horizontal line of sight, then the said
horizontal bright line across the right-hand half of the width of the field of
view will appear broad and coarse, at the same time that the intended com-
mencement of the said line across the left-hand half of the width of the field
of view will disappear altogether, and it will be only when the vision is truly
directed through the central axis of the tube Y that the said bright line will
appear equally clear and defined, and extending quite uniformly across both
balves of the field of view, as already described. Note.-The metal cells or
rings, wherein the glasses P and Q are fixed, are fitted into each end of the
tube Y, so as to be capable of turning round therein, in order to adjust the
position of the two glasses, in manner aforesaid, so that the said bright line
will be horizontal across the field of view; and for the convenience of making
such adjustment, screws p, p, are applied at each end of the tube Y, in the
direction of the tangents, to each of the rings P, Q; and the threads of those
screws p, p, act in the manner of endless screws in teeth which are f. rmed
around the outside circumference of the metal rings wherein the glasses P, Q,
are fixed, so that by turning the screws p the said rings and the glasses which
they contain will be turned round within the ends of the tube Y. And in
order to afford a sufficient view of the object which is to be seen through the
glasses P, Q, at each end of the tube Y, to enable the observer to identify
such object, the middle part of the field of view is left open, as is sufficiently
explained by Figure 4 and Figure 3, the upright sides of the several darkened
quadrants 1, 3, and 5, 7, being removed at a small distance from the vertical
centre line or diameter of the field of view, but parallel to that diameter,
wherefore the appearance to the eye, in looking through the tube Y, will be
an opening in form of an upright cleft across the centre of the field of view
from top to bottom thereof, and of sufficient width to allow the object which

page_text: is to be viewed to be distinguished, also the bright narrow line of light before
mentioned extends horizontally across the field of view at the level of its
centre, from side to side, but not across the upright cleft. When the instru
ment is held, as shewn in Figure 1, in a proper position for observing an
altitude, the central line of sight y through the tube Y is in exact conformity
with the central line of the telescope A, which line is directed to look exactly
to the central line before mentioned as being scratched on the mirror D, and
which seratched line will be horizontal when the instrument is held by its
handle W with the plane of its divided arch B, B, in a vertical direction.
The said scratched line will be visible to the observer looking through the
telescope A, for it will appear to cross the upright cleft in the middle of the
field of view; and when the instrument is held by its bandle W with
the telescope A in a truly horizontal direction, then the line of sight through
the tube Y will conform exactly with the central line of the telescope A, and it
will be known that such is the case by the appearance of the bright horizontal
line which, as before mentioned, extends from each side of the field of view,
through the glasses P, Q, of the tube Y, and that bright line will appear to
be continued across the upright cleft, in the middle of the field of view, by
the said line that is scratched on the mirror D, so that the aforesaid bright
line proceeding from each side of the field of view and the scratch on the
mirror at the centre of the field will form one fine continuous line, extending
horizontally all across the centre of the field as a horizontal diameter thereto.
When that appearance is obtained it will be known that the instrument is in
its true intended position, as in Figure 1; then by moving the index II upon
the divided arch B, B, the mirror D can be inclined more or less, as may be
requisite for reflecting the ray, coming in the direction of the dotted line a,
from the object whereof the altitude is to be observed, and turning that ray
by reflection into the horizontal line of sight y which passes through the
centre of the tube Y, and of the telescope A; and the index I being clamped
by its clamp screw, and then adjusted by its slow-motion screw t (as is usual
in sextants), until the image of the object in the mirror D corresponds to the
line before mentioned, which extends horizontally across the field of view as
a horizontal diameter thereto, then the divisions on the arch B, B, being read
off by the vernier r of the index H, will give the measurement of the
angle x, D, y, of altitude of the object x above the horizontal line y, y.
R are dark glasses of the same kind as are usually applied to sextants for
the purpose of observing the sun; they can be all turned up out of the way,
or one, or two, or three can be turned down into the line y, y, as is apparent
in Figure 1. The telescope A is applied to the instrument by screwing it

page_text: into a ring G which is formed on the end of a stem fitted into a socket, and
adjustable therein by a screw for placing the telescope nearer to or farther
from the plane of the divided areh B, B, as may be required, and as is
commonly done in sextants.
The mirror D is mounted on the central part of the index H in the usual
manner of sextants, with the usual screws for adjusting the position of its flat.
surface to be exactly perpendicular to the plane of the divided arch B, B;
also with setting screws at q. q, for turning the plane of the mirror D to an
exact coincidence with the radial line h, h, and thus producing the adjustment
for what is termed index error, that is to say, when the vernier r of the
index II is at its zero then the plane of the mirror D should be exactly at
right angles to the line of sight y. y. And note. The mirror D cannot be
made of glass silvered at the back, as is usual in sextants and reflecting
instruments, but it must be made of the compound metal called speculum
metal, being such as is used for the speculum of a reflecting telescope, the
mirror D being ground to a perfectly flat surface and well polished.
The divisions on the arch B, B, are continued to 80 degrees and upwards,
being numbered double, so as to read 160 degrees, for the instrument is capable
of measuring altitudes or other angles as great as 160 degrees, which will be
found a great advantage over the ordinary reflecting instruments.
Figures 5, 6, 7, 8, 9, of the Drawing are full-size representations of another
form of my said improved instrument adapted for the use of military or civil
engineers and surveyors in field surveying, being extremely portable and
convenient, and sufficiently accurate for such uses. The instrument is con-
structed in the form of the well-known mathematical instrument called a
sector, consisting of two legs H, I, united by a large joint B in the manner
of a short but broad and thick pocket rule. The whole when shut up is of
the dimensions represented in Figure 5, and can be enclosed in a leather case,
Figures 7 and 8, for carrying in the pocket, that leather case opening or
shutting up in the manner of pocket-book lids, and being fastened when
closed by inserting a pencil w into loops u, u, as is commonly done for
fastening pocket books. When in use the two legs H and T are opened out
to an angle one with the other, as in Figure 6, which angle is denoted by the
divisions engraved around the circular joint B, B. A plain mirror D of
speculum metal is lodged for carriage (as shewn by dotted lines in Figure 5),
within a cavity in the thickness of the leg T where withdrawn therefrom.
The mirror D is stuck for use into a notch formed for its reception at the
central part of the circular joint B, B, so that the mirror D will stand with
its plane at right angles to the plane of the two legs T, H, and their arch;

page_text: B, B, and the mirror will also stand with its plane at right angles to the
inside edge h, k, of the leg H, which line h, h, radiates out from the divisions
of the arch B, B, at the zero of those divisions. The surface of the mirror D
coincides exactly with the centre of the circle B, B; and a line is scratched
on the surface of the mirror D, so that when the mirror is in place for use the
said line passes exactly through the centre of the circle B, B, and in a
direction at right angles to its plane, in the same manner as already explained
in respect to Figure 1. When the instrument, Figures 5, 6, is to be used for
measuring an angle of altitude, a horizontal line is derived from a pendulum
K, m, Y, which is suspended freely on a small pin that projects out at a, from
the flat surface of the leg T, and the upper part Y of the pendulum serves as a
horizontal line of sight y, y, that part Y being adapted to be exactly horizontal
when the whole pendulum K, m, Y, hangs freely, as aforesaid, on its pin a, see
Figures 6 and 10. That pendulum is a small drawing square cut out of
metal plate in the form of the letter L, and is lodged for carriage in a cavity
within the thickness of the leg H, as shewn by the dotted lines in Figures 5
and 6. The end of the part Y of the square then projects from the leg II across
the end of the other leg T, being received in a cavity at that end, and by thus
passing across the ends of both legs I and T the part Y unites them securely
when they are closed together, as in Figure 5. The said square K, m, Y, can
remain secure in its said cavity in the leg H when the instrument is in use, but
can be withdrawn whenever it is wanted, either for a drawing square or for
raising perpendiculars, or for use as a pendulum in manner aforesaid. The
sight of the observer is directed in a horizontal line y, y, Figure 6, through a
long narrow slit cut out through a thin blade A of metal, which turns up on
suitable joints, so as to stand out at right angles to the plane of the instrument
and its divided arch B, B, as is shewn in Figures 9 and 10. The said cleft
in the blade A ranges exactly with the innermost edge of the leg T, and with
the upper part Y of the pendulum K, m, Y, which upper part Y, when the
instrument is held with its leg T in a truly horizontal position, will point
exactly to the line which, as before mentioned, is scratched on the surface of the
mirror D. When the observer holds the instrument in his hand, in the position,
Figure 10, and looks through the slit in the sight A along the line of sight y, y,
towards the line that is scratched on the mirror D, if he sees that the straight
line along the upper part Y of the pendulum K, m Y, conforms exactly with s
that line of sight y, y, he knows that the said line y, y, is horizontal; but if
the said upper part Y does not so conform, he must tilt the whole instrument
so much one way or other as will bring it to conform, and then the line of
sight y, y, and the leg T will be truly horizontal and is to be kept so. The

page_text: other leg of the instrument is then to be moved up or down about the
centre of the arch B until the reflected image of the object a, whereof the
altitude is to be observed, is seen exactly at the scratch in the mirror D. The
divisions of the arch B, B, will shew the real angle that the two legs II and T
make one with the other, and the required angle a, D, y, of altitude of
the objecta above the horizontal line y, y, will be double that real angle
which the two legs H and T make one with the other. The divisions
of the arch B, B, may be numbered to read double the real angle that
the two legs make one with the other, and those divisions will shew the
required angle of altitude a, D, y. The instrument may have two sets of
divisions around the circumference of the arch B, B, one at each side of the
thickness of the instrument, one set of those divisions being numbered in real
degrees to shew the angle that the two legs II and T make one with the
other; and the other set of those divisions being numbered to shew twice as
much, which latter numbering will denote the angle x, D, y, actually measured
by the reflection. And each set of divisions may have a vernier scale engraved
on the leg T, where the same applies against the circumference of the arch
B, B, in order by such vernier to subdivide the divisions of the arch B, B.
And note. The notch before mentioned wherein the mirror D is mounted for
use, instead of being made in the central part of the leg H, may be formed
across the centre of a large joint pin b, which serves for the centre of motion,
whereby the two legs II and T are united, and which joint pin bis fastened to
and moves with the leg I; but the said joint pin & will admit of a small
extent of angular motion in respect to the leg H, for the purpose of adjusting
the position of the mirror D; such motion may be given by a small setting
screw 7, 9, Figure 12, which is mounted in a cavity formed within the
thickness of the leg II near the circumference of the arch B3, B, as is shewn by
the dotted lines in Figure 6, and that screw q acts upon the end of an arm f,
which extends out from the said large centre pin 6 of the joint. The setting
is wholly concealed, but it can be turned by means of a watch key,
and will serve to adjust the position of the mirror D for index error, in
the same manner as already described, respecting the setting screws q, q,
Figure 1, viz., to place the mirror D with its surface in a direction exactly
across at right angles to the length of that leg H, wherewith the mirror moves
when the legs H and T are opened out with angular motion around their joint
pin b, so as to set one leg at any angle with the other leg. The instrument
may also be used for the measurement of horizontal angles, in the manner
shewn in Figure 11, in which case a magnetic needle is very useful for
determining bearings, or measuring the horizontal angles that objects make
screw

page_text: with the magnetic meridian. A magnetic needle n, s, is for such purpose
contained in a small box N which is lodged in a notch cut out in the inside
edge of the leg T, the box N being retained in place within that notch by
centre pins situated in the middle of the thickness of the leg T, and one of
those pins entering into each end of the box N at one-fourth of the width of
the box N from that edge or side thereof, which (when the box N is in its
place so as to completely fill up the notch in the leg T) will conform with the
innermost straight edge of that leg. The whole width of the box N is twice
as much as its thickness, which thickness is equal to the thickness of the
leg T wherein the box is included. The box N contains the magnetic needle
n, s, within it, the centre pin wherein it is mounted being fixed up in a small
cross bar at the mid length of the box N. A cover of transparent talc and a
bottom of the same material encloses the needle n, s, to complete the box, but
there is also a cover A and a bottom C of metal, both united to that end of
the box which is farthest from the arch B by a hinge joint for each cover A
and C, so that about those hinge joints the said covers A and C can be turned
up into a direction at right angles to the length of the box N, in order to
uncover the box, and also in order to erect the cover A into a suitable position
for becoming the blade A, before mentioned as having a long narrow slit
through it for directing the sight in making an observation; but that whereas
it is requisite for that purpose that the slit which is in the mid breath of the
blade or cover A should range or conform with the inner edge y, y, of the
leg T, the whole of the box N requires to be turned half round about its two
centre pins before mentioned, whereby it is kept in place within its notch in
the leg T; those centre pins being situated as already stated form an axis
whereon the box N is sustained, and when it is turned with one of its sides
upwards the box N will exactly fill up its notch in the leg T, as is seen in
Figure 5, and then the two metal covers A and C of the box being shut down,
they will conform to the two flat surfaces of the leg T. But by turning the
box N half round about its said axis or centre pins, it will assume the position
seen in Figure 6, the mid breath of the box N then conforming to the line
y. y, and consequently when the covers of blades A and C of the box are
opened up to a right angle with the length of the box N, the slits through
them will conform to the line of sight y, y, suitably for making an observation
for measurement of an altitude in manner already described, or else for
measuring a horizontal angle in manner following, by aid of the magnetic
needle n, s. The tale at top and at bottom of the box N allows the needle
n, s, to be seen very distinctly by the eye, when looking through the slit in the
blade A so as to observe the direction of the needle. The whole instrument is

page_text: to be turned round about in a horizontal direction to direct the line y, y, to all
quarters of the compass in succession, until the needle n, s, is seen to be in its
quiescent direction, that is, in the magnetic meridian, and then the instrument
is turned so much further as will cause the needle to point correctly along the
line y, y, that is, directly towards the line scratched on the surface of the
mirror D. Then keeping the instrument steady and still, looking along the
line y, y, in the direction of the needle n, s, the leg H is to be turned at an
angle about the centre of the arch B, until the object whereof the bearing is
to be determined is seen by reflection in the mirror D, and then the bearing
or angle that the direction from the eye to such object makes with the
magnetic meridian will be double the angle that the two legs II and T
make one with another, which double angle will be shewn by the readings
of the vernier against those divisions of the arch B which are adapted
for reading off double the angle, as already explained.
By this mode
the angle of bearing can be measured if the object is situated on the
right-hand side of the magnetic meridian, but if it is on the left-hand side
thereof then the leg II is to be opened about the centre of the arch B, B,
beyond a right angle with the other leg T, in order to bring the back surface
of the mirror D into use for reflecting a ray from an object situated on the
right-hand side of the magnetic meridian, and bending that ray into the
direction of the line of sight y, y, that direction being, as before explained,
coincident with the magnetic meridian. The back surface of the mirror D
must for this purpose be made truly flat like the front surface and parallel
thereto, the thickness of the mirror being alike at all parts, and as the back
surface is not coincident with the centre of the arch B, it cannot have a line
scratched upon it for determining the line of sight y, y, as already described
respecting the front surface. Therefore in lieu of such a scratched line an
extra sight piece, Figure 11, is turned up from the inner edge of the leg T
about a centre pin by which it is jointed to that edge, so that the said sight k
will stand up perpendicularly to the plane of the leg T, and the upright edge
of that sight will serve to direct the view truly along the line y, y, in
looking through the slit of the blade A towards the back surface of the mirror
D, and the object which is to be seen by reflection in that surface is to be
brought to apparent bisection or contact with the said upright edge of the
sight. The sight k, when turned down to coincide with the edge of the
leg T, forms a door to close the entrance of the cavity in the leg T wherein
the mirror D is lodged for carriage. The magnetic needle n, s, may be put
into its box N, either with the north end or its south end directed towards the
mirror D, and in one case the bearings will be measured from a northward

page_text: and in the other case from a southward direction. As the blade A stands up
to a considerable height above the upper surface of the leg T, and the other
blade C descends down as much below the lower surface of the same leg (as
is seen in Figure 11), their long vertical slits permit of directing the sight
somewhat downwards or upwards in order to see by reflection in the mirror D
objects that are rather below or above the horizontal plane in which the legs
of the instrument must be retained when making the observation, and it will
measure the horizontal angles of bearing of such objects with the magnetic
meridian; and if it is desired to measure the angle subtended by two objects,
whereof one is to be viewed by direct vision and the other by reflection, the
mirror D may be of half the width represented in the Drawings, so that its
edge will terminate exactly where the line before mentioned would be scratched
upon its surface, that line being coincident with the center of the circular
arch B, B, wherefore in the case now describing it will be one edge or termi-
nation of the front surface of the mirror, which will be thus coincident with
the centre of the arch B, B, in order that one object may be seen by direct
vision along the line of sight y, y, through the slit of the blade A, and against
the said edge or termination of the mirror D, whilst the other object which is
viewed by reflection in the front surface of the mirror is brought at the very
edge or termination of that surface to an apparent contact with a direct view
of the other object against the same edge. The whole instrument, Figures 5
and 6, being constructed like a sector may have engraved on its legs T and H
any such lines of divisions belonging to an ordinary sector as are or may be
desired. Also the square K, Y, may have lines of equal divisions engraved
along its edges, in order that by applying the side Y of that square to the
inside of one of the legs T or H, as is shewn by dotted lines in Figure 6, and
opening the two legs H and T to make any required angle with each other,
the instrument may be used to construct and find the proportions of any
right-angled triangle. The instrument also serves as a rule or measure and
for a bevel, and by using the square K, Y, as a pendulem it serves for a level
or for a clinometer, thus rendering it of general use in field operations, as well
as for the measurement of angles in the manner herein-before described.
And note. The instrument, when constructed as in Figure 1, may have the
pendulum K with the box I, Figure 2, which contains it, together with the tube
And then
of sight Y, Y, altogether removed from the instrument, Figure 1.
a compas box containing a magnetic needle may be applied in the place of the
tube Y, Y, to enable the instrument, Figure 1, to measure horizontal angles of
bearing with the magnetic meridian in the same manner as already described
in respect to Figures 5, 6.

page_text: Having now described my said improved instrument, I, the said Frederick
Augustus Glover, 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 :-
Firstly, in the mode herein-before described of measuring angles by means
of one reflection in one mirror, instead of by two reflections in two mirrors, as
heretofore practised in reflecting instruments.
Secondly, in the mode herein-before described of applying to the instrument
a horizontal line of sight which is governed by the gravitation of a pendulum,
so as to refer the altitude of an object which is viewed by one reflection in one
mirror to a horizontal line without requiring a view of the horizon of the sea
or any artificial horizon, as usually practised.
Thirdly, in the mode herein-before described of applying to the instrument
a magnetic needle which is viewed at the same time with the object that is
viewed by one reflection in one mirror, so as to refer the angle of bearing or
direction of that object to the magnetic meridian.
Fourthly, in the mode herein-before described of measuring angles by
means of one reflection in one mirror, and the apparent contact of the image
of an object reflected at the very edge or termination of the reflecting surface
of that mirror, that contact being made with a direct vision of another object
by the same edge or termination of the said reflecting surface of that
mirror.
In witness whereof, I, the said Frederick Augustus Glover, have hereunto
set my hand and seal, this Second day of May, in the year of our
Lord One thousand eight hundred and forty.
FREDERICK AUGUSTUS (L.S.) GLOVER.
AND BE IT REMEMBERED, that on the Second day of May, in the
year of our Lord 1840, the aforesaid Frederick Augustus Glover came
before our said Lady the Queen in Her Chancery, and acknowledged the
Specification aforesaid, and all and every thing therein contained and specified,
in form above written. And also the Specification aforesaid was stamped
according to the tenor of the Statute made for that purpose.
Inrolled the Second day of May, in the year of our Lord One thousand
eight hundred and forty.