IMPROVE- MENTS IN SEXTANTS AND OTHER SIMILAR INSTRUMENTS FOR TAKING OBSER, VATIONS
Year: 1864

page_text: LETTERS PATENT to Richard Archibald Brooman, of 166, Fleet Street, in
the City of London, Patent Agent, for the Invention of "IMPROVE-
MENTS IN SEXTANTS AND OTHER SIMILAR INSTRUMENTS FOR TAKING OBSER,
VATIONS."A communication from abroad by Pierre Michel Albert
Laurent, of St. Nazaire, France.
Sealed the 3rd February 1865, and dated the 27th October 1864.
PROVISIONAL SPECIFICATION left by the said Richard Archibald Brooman
at the Office of the Commissioners of Patents, with his Petition, on the
27th October 1864.
I, RICHARD ARCHIBALD BROOMAN, of 166, Fleet Street, in the City of
5 London, Patent Agent, do hereby declare the nature of the said Invention
for "IMPROVEMENTS IN SEXTANTS AND OTHER SIMILAR INSTRUMENTS FOR TAKING
OBSERVATIONS," to be as follows:-
The object of this Invention is the rendering of the measure of angular
distances by means of reflecting instruments, octants, sextants, and circles,
0 more easy and more exact than heretofore, especially in night observations.
The Invention consists in improvements in these instruments which allow
of the observer lengthening perpendicularly to the plane of the instrument,
according to the requirements of the observation, one or other of the direct or

page_text: reflected images of the terrestial objects or heavenly bodies, the angular dis-
tance of which is being measured, or even both these images. When the
elongated heavenly body is a star it appears in the form of a luminous line
perpendicular to the plane of the instrument; when the heavenly body is the
sun or a planet, it appears as a luminous band, more or less broad according to
its diameter. The effects just described are obtained by means of a simple
apparatus which I term an elongating glass, or by a modification in the shape,
hitherto plain, of the mirrors used in reflecting instruments. The accessory
apparatus for elongating the images, and termed elongating glass is a con-
verging or diverging cylindrical lens placed upon the instrument normally to
its plane, and perpendicularly to the course' of the luminous rays of the object
to be elongated. By cylindrical lens I mean all lenses, the faces of which
are cut or ground to a cylindrical instead of a spherical curve as ordinary
lenses, the lenses may be plano-convex, plano-concave, double convex, double
concave, or convexo-concave.
In the accompanying Drawings A, A, A, B, B, B, C, C¹, C, D, D¹, D¹¹³,
E, E', E", represent these different glasses in their frames. A, B, C, D, E,
are cross sections of the elongating glasses through a transverse section per
pendicular to the generators of their cylindrical surfaces; A¹, B, C, D, E¹,
are transverse sections through a plane parallel to the generators of their
cylindrical surfaces; A", B", C", D", E", are longitudinal sections of the
elongating glasses. The interposition of such a glass between the eye and the
heavenly body or a terrestial object, will have the effect of elongating more or
less according to its focal length (its distance to the eye, and the opening of
the pupil) the image of the object or body in a perpendicular direction to the
generators of the cylindrical surface of the lens. By placing upon a reflecting
instrument an elongating glass, the generators of which are parallel to its
plane, the body or object seen through this elongating glass will present to
the eye those of its edges, which are parallel to the plane of the instru-
ment, confused and indistinct, while those of its edges which are perpen-
dicular to the plane of the instrument, those precisely between which contact
is established, will preserve all their sharpness, whether observed with the naked
cye or through a glass. The elongating glasses for objects or bodies seen by
reflection only are placed at C or D, Figure 1, between the large mirror A
and the small mirror B, in the same manner as the coloured glasses are
placed in reflecting instruments. The elongating glasses for objects or bodies
seen directly are placed at C' or D' above the small mirror B with respect to
the eye. The elongated glasses for objects or bodies seen directly and by
reflection at the same time, are placed between the eye and the small mirror B,

page_text: say, for example, C", Figure 1. The frames for holding the elongating glasses
may be fixed to the instrument, and movable on a hinge as D and D', Figure 1..
This arrangement allows the observer to move into the path of the luminous
rays the particular elongating glass suitable for the observation; the frames
are then similar to that indicated at Figure H. The frames may also bo.
independent of the instrument, and are then similar to that shewn at Figure M,.
the tail N is introduced into one or other of the holders C, C, C", Figure 1.
The frames are constructed in manner to allow the observer by a slight rotary
motion of the lens to re-establish the parallelism of its generators with or to
the plane of the instrument, this is indispensable to exactitude in the obser-
vations. Figures H and M shewn one of the arrangements for fulfilling this,
condition. The dimension or opening to be given to the elongating glasses
is determined by the same rule as that which fixes the dimension of the
coloured glasses, that is to say, that the opening or field of these glasses must
be such that all the luminous rays that the deformed body sends to the eye may
pass through them, and without their intercepting any of them. The focal
length to be given to the elongating glasses depends upon the angle that the
image is desired to subtend in the eye, upon the distance of the lens to the
eye, and on the opening or diameter of the pupil. Experience will dictate
better than all theoretical formulæ the most suitable focal length to be given to
the elongating glasses. The light of the body elongated diminishing all things
equal in proportion to its elongation, it is advisable to furnish each instru-
ment with a series of elongating glasses of different powers in order that the
observer may select that most suited for his observation. Again, the elonga-
tion may be varied by altering the distance between the eye and the elongating
glass if the observation is with the naked eye, or between this glass and the
object if of the telescope if a lelescope is used. To measure the angular height
of a star above the horizon of the sea, look directly to the horizon, and place
an elongating glass between the large and small mirrors, when the star will
be brought in the form of a luminous line perfectly sharp, without irradiation
and without trepidation to rest upon the line of the horizon. To measure the
angular distance from the moon to a star, look directly at the latter, and place
an elongating glass behind the small mirror, the lighted edge of the moon
which will retain her natural shape, will be brought to tangent upon the linear
image of the star. To measure in the artificial horizon the height of a star,
place an elongating glass between the eye and the small mirror, and the
linear image of the star seen by reflection in the small mirror will be brought
superposed over the linear image of the same star seen in the artificial horizon.
These various observations afford a degree of exactitude not attainable without

page_text: the aid of elongating glasses. The position of the elongating glasses between
the large and small mirrors being arbitrary, it may be supposed as the extreme
limit to be fixed on one of the plain faces anterior or posterior of these
mirrors, equivalent to dressing in cylindrical surfaces parallel to the plane
of the instrument, either the anterior face or the posterior face of one or
other of these mirrors, or their two faces. Again, the position of the elon-
gating glass placed between the small mirror and the eye being arbitrary, it
may be supposed applied on the plain face of one of the lenses composing the
telescope equivalent to dressing upon this face of the lens a cylindrical
surface parallel to the plane of the instrument, and to converting it into a
cylindro-spherical lens. In reflecting instruments for measuring at night the
angular height of the stars above the horizon of the sea, it is better, in order
to lose as little light as possible, to dispense with the non-silvered párt of the
small mirror, and to give to the Galileo telescope the greatest opening
possible.
SPECIFICATION in pursuance of the conditions of the Letters Patent, filed
by the said Richard Archibald Brooman in the Great Seal Patent Office
on the 2nd March 1865.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, RICHARD
ARCHIBALD BROOMAN, of 166, Fleet Street, in the City of London, Patent
Agent, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Twenty-seventh day of October, in the year
Lord One thousand eight hundred and sixty-four, in the twenty-eighth year of
Her reign, did, for Herself, Her heirs and successors, give and grant unto me,
tho said Richard Archibald Brooman, Her special licence that I, the said
Richard Archibald Brooman, my exccutors, administrators, and assigns, or
such others as I, the said Richard Archibald Brooman, executors, admi-
nistrators, and assigns, should at any time agree with, and no others, from
time to time and at all times thereafter during the term therein expressed,
should and lawfully might make, use, exercise, and vend, within the United
Kingdom of Great Britain and Ireland, the Channel Islands, and Isle of Man
an Invention for "IMPROVEMENTS IN SEXTANTS AND OTHER SIMILAR INSTRUMENTS
FOR TAKING OBSERVATIONS," (communicated to me from abroad by Pierre
mo
Michel Albert Laurent, of St. Nazaire, France,) upon the condition (amongst
others) that I, the said Richard Archibald Brooman, my executors or admi-

page_text: nistrators, by an instrument in writing under my, or their, or one of their
hands and seals, should particularly describe and ascertain the nature of
the said Invention, and in what manner the same was to be performed,
and cause the same to be filed in the Great Seal Patent Office within six
calendar months next and immediately after the date of the said Letters
Patent.
.
NOW KNOW YE, that I, the said Richard Archibald Brooman, do
hereby declare the nature of the said Invention, and in what manner the same
is to be performed, to be particularly described and ascertained in and by the
following statement thereof, reference being had to the Drawings hereunto
annexed, that is to say :-
.The object of this Invention is the rendering of the measure of angular
distances by means of reflecting instruments, octants, sextants, and circles,
more easy and more exact than heretofore, especially in night observations.
The Invention consists in improvements in these instruments, which allow
of the observer lengthening perpendicularly to the plane of the instrument,
according to the requirements of the observation, one or other of the direct
or reflected images of the terrestrial objects or heavenly bodies, the angular
distance of which is being measured, or even both these images. When the
elongated heavenly body is a star it appears in the form of a luminous line
perpendicular to the plane of the instrument; when the heavenly body is the
sun or a planet. it appears as a luminous band, more or less broad according
to its diameter. The effects just described are obtained by means of a simple
apparatus, which I term an elongating glass, or by a modification in the shape,
hitherto plain, of the mirrors used in reflecting instruments. The accessory
apparatus for elongating the images, and termed elongating glass, is a con-
verging or diverging cylindrical lens place upon the instrument normally to its
plane, and perpendicularly to the course of the luminous rays of the object to
be elongated. By cylindrical lens I mean all lenses the faces of which are cut
or ground to a cylindrical instead of a spherical curve, as ordinary lenses; the
lenses may be plano-convex, plano-concave, double convex, double concave,
or convexo-concave.
In the accompanying Drawings, A, A, A, B, B, B, C, C¹, C, D, D',
D", E, E¹, E", represent these different glasses in their frames. A, B, C,
D, E, are cross sections of the elongating glasses through a transverse section
perpendicular to the generators of their cylindrical surfaces; A¹, B¹, C¹, D¹,
E¹, are transverse sections through a plane parallel to the generators of their
cylindrical surfaces; A", B", C", D", E", are longitudinal sections of the
elongating glasses. The interposition of such a glass between the eye and the

page_text: heavenly body or a terrestrial object will have the effect of elongating, more
or less according to its focal length (its distance to the eye and the opening
of the pupil), the image of the object or body in a perpendicular direction to
the generators of the cylindrical surface of the lens. By placing upon a
reflecting instrument an elongating glass, the generators of which are parallel
to its plane, the body or object seen through this elongating glass will present
to the eye those of its edges, which are parallel to the plane of the instru
ment, confused and indistinct, while those of its edges which are perpendicular
to the plane of the instrument, those precisely between which contact is
éstablished will preserve all their sharpness, whether observed with the naked
eye or through a glass. The elongating glasses for objects or bodies seen by
feflection only, are placed at C or D; Figure 1, between the large mirror A
and the small mirror B, in the same manner as the colored glasses are placed
in reflecting instruments. The elongated glasses for objects or bodies seen
directly are placed at C¹ or D¹ above the small mirror B with respect to the
eye. The elongated glasses for objects or bodies, seen directly and by reflection
at the same time, are placed between the eye and the small mirror B, say, for
example, at C, Figure 1. The frames for holding the clongating glasses
may be fixed to the instrument, and movable on a hinge, as D and D¹,
Figure 1. This arrangement allows the observer to move into the path of
the luminous rays the particular elongating glass suitable for the observation ;.
the frames are then similar to that indicated at Figure H. The frames may:
also be independent of the instrument, and are then similar to that shewn at
Figure M; the tail N is introduced into one or other of the holders C, C¹, C",
Figure 1: The frames are constructed in manner to allow the observer by a
slight rotary motion of the lens to re-establish the parallelism of its generators
with or to the plane of the instrument; this is indispensable to exactitude in
the observations. Figures H and M shew one of the arrangements for
fulfilling this condition. The dimension or opening to be given to the elon-
gating glasses is determined by the same rule as that which fixes the
dimensions of the colored glasses, that is to say, that the opening or field of
these glasses must be such that all the luminous rays that the deformed body
sends to the eye may pass through' them, and without their intercepting any
of them. The focal length to be given to the elongating glasses depends upon
the angle that the image is desired to subtend in the eye, upon the distance
of the lens to the eye, and on the opening. or diameter of the pupil. Expe-
rience will dictate, better than all theoretical formula, the most suitable focal
lengths to be given to the elongating glasses. The light of the body elongated
diminishing all things equal in proportion to its elongation, it is advisable to

page_text: furnish each instrument with a. series of elongating glasses of different powers,
in order that the observer, may select that most suited for his observation.
Again, the elongation may be varied by altering the distance between the eye
and-the elongating glass, if the observation is with the naked eye, or between
this glass and the object if of the telescope if a telescope is used. To measure
the angular height of a star above the horizon of the sea, look directly to the
horizon and place an elongating glass between the large and small mirrors,
when the star will be brought in the form of a luminous line perfectly sharp
without irradiation and without trepidation. to rest upon the line.of.the
horizon. To measure the angular distance from the moon to a star, look
directly at the latter, and place an elongating glass behind the small mirror,
the lighted edge of the moon, which will retain her natural shape, will be
brought to tangent upon the linear image of the star. To measure in the
artificial horizon the height of a star, place an elongating glass between the
eye and the small mirror, and the linear image of the star seen by reflection
in the small mirror will be brought superposed over the linear image of the
same star seen in the artificial horizon. These various observations afford a
degree of exactitude not attainable without the aid of elongating glasses. The
position of the elongating glasses between the large and small mirrors being
arbitrary, it may be supposed, as the extreme limit to be fixed on one of the
plain faces, anterior or posterior, of these mirrors, equivalent to dressing in
cylindrical surfaces parallel to the plane of the instrument, either the anterior
face or the posterior face of one or other of these mirrors, or their two faces.
Again, the position of the elongating glass placed between the small mirror
and the eye, being arbitrary, it may be supposed applied on the plain face of
one of the lenses composing the telescope equivalent to dressing upon this
face of the lens a cylindrical surface parallel to the plane of the instrument
and to converting it into a cylindro-spherical lens. In reflecting instruments
for measuring at night the angular height of the stars above the horizon of
the sea, it is better, in order to lose as little light as possible, to dispence with
the non-silvered part of the small mirror, and to give to the Galileo telescope
the greatest opening possible.
And having now described the nature of the said Invention, and in what
manner the same is to be performed, I declare that I claim,-
First, the improvements herein-before described in sextants and other
similar instruments for taking observations, whereby the observer is enabled
to lengthen perpendicularly to the plane of the instrument the direct or the
reflected image of a heavenly body or other object, the angular distance of
which is to be measured, or even both these images.

page_text: Second, the employment in sextants and other similar instruments of
elongating glasses or lenses, in manner and for the purpose herein-before
described.
In witness whereof, I, the said Richard Archibald Brooman, have here-
unto set my hand and seal, this First day of March, One thousand
eight hundred and sixty-five.