IMPROVEMENTS IN INSTRUMENTS FOR MEASURING ANGLES. APPLICABLE TO NAUTICAL AND OTHER PER
Year: 1858

page_text: LETTERS PATENT to Louis Joseph Arsène Brun, of Paris, in the Empire
of France, Merchant, for the Invention of "IMPROVEMENTS IN INSTRUMENTS
FOR MEASURING ANGLES. APPLICABLE TO NAUTICAL AND OTHER PER"
FOR MEASURING ANGLES. APPLICABLE TO NAUTICAL AND OTHER P
Sealed the 29th June 1858, and dated the 1st January 1858.
PROVISIONAL SPECIFICATION left by the said Louis Joseph Arsène
Brun at the Office of the Commissioners of Patents, with his Petition,
on the 1st January 1858.
I, LOUIS JOSEPH ARSENE BRUN, of Paris, in the Empire of France, Merchant,
do hereby declare the nature of the said Invention for "IMPROVEMENTS IN
INSTRUMENTS FOR MEASURING ANGLES, APPLICABLE TO NAUTICAL AND OTHER PUR-
POSES," to be as follows:
This Invention relates to a compensating protractor which allows of at once
placing on paper (flat or hydrographical maps, topographical surveys, plans,
&c.,) with regard to the meridian, the angles or directions measured in nature
with a magnetic needle or a compass in reference to the magnetic meridian,
and that without taking into account the variation or declination of the
magnetic needle at each operation. Thus, and to be more intelligible, if it be a
topographical compass, this new protractor allows of the tracing immediately on
paper, and without other aid than that of the meridians already marked thereon,
the projection itself of directions seen in nature; if it be a mariner's compass,

page_text: it allows of the tracing at once, and without calculation, either the direction
travelled or a bearing taken, &c. In a word, the compensating protractor is
merely an ordinary protractor in which the graduation is, at the will of the
operator, moveable or fixed with regard to the true line. It is composed of,
first, a first transparent plate or table (horn, glass, &c.), two sides a, b, and
c, d, Fig. 1, of which (which I call rules) are exactly parallel to each other,
and also to a line e, f, traced on the plate (which I call the true line). This
true line is made near the middle of the table, Fig. 1 of the Drawings
annexed, if the second plate or limb herein-after referred to is circular; it is,
on the contrary, near one of the rules Fig. 2, if the limb is semicircular, or
when it is desired to employ a circular limb of greater diameter than the table.
The two rules or only one of them may be furnished with a metal or wooden
border, either moveable or not, as shown in Fig. 2, but this is not of great utility.
The table is besides pierced with two holes g, h, Figs. 1, 2, 6, 7, and 8, or
it may be a groove or part cut out, Fig. 3, intended to receive screws, Fig. 5,
the heads of which (which are very flat) are placed below the table, and on
which a nut is screwed, Fig. 4, the pressure of which suffices to hold and fix the
limb herein-after referred to on the table. These holes are so arranged that
the centre of the limb held by the screws may be placed on the true line.
Although the arrangement of grooves, Fig. 3, seems advantageous at first,
because it allows of the using limbs of different diameter on a single table,
yet I prefer the system of holes, because the screws are less liable to be lost,
and also because it is easier to work the limb. Secondly, a second plate (the
limb), which is also transparent; it may be circular or semicircular, and is
graduated. This limb is so placed on the table that its centre is on the true
line, then by making it turn on the table, any graduation desired can be
made to coincide with the true line, and then the screws are tightened. By
this means a protractor is produced, the zero radius of which is inclined to
the rule at the angle required.
All modes of graduation at present in use may be applied to this instru-
ment, but when it is more particularly intended for marine purposes, it is well
to adopt a graduation exactly analogous to that of the mariner's compass, the
mariner's card included, the north line of which coincides with the zero radius.
The limb may be circular and of smaller diameter than the table, Fig. 6;
or circular and of greater diameter than the table; Fig. 7; or lastly; semi-
circular, as at Fig. 8. In these three Figures 6, 7, and 8, the zero radius
of the limb is supposed to be superposed on the true line of the instrument.
It is advantageous to leave a sort of margin, about an inch or an inch and
a half wide, round the whole circumference of the limb; this margin prevents

page_text: the nuts resting on and injuring the graduations. This arrangement is repre-
sented at Fig. 9.
A number of modifications can be made in this instrument; thus, if thought
advisable, a vernier scale can be added at the right and left of the true line, to
show with less or greater approximation the fractions of the last subdivisions
of the limb. This instrument may be constructed of copper or any other
metal, care being taken to render apparent the centre of the limb, Fig. 10,
In this case the limb may be submitted to the action of adjusting screws,
which will render its movements extremely slow. Lastly, the form may easily
be varied, as seen in the instrument represented at Fig. 10, in which the
dark tint indicates the limb, and the yellow indicates the table and rule. It
is also evident that in this same Figure the true line is the diameter e, f,
parallel to the rule a, b..
SPECIFICATION in pursuance of the conditions of the Letters Patent, filed
by the said Louis Joseph Arsène Brun in the Great Seal Patent Office
. on the 30th June 1858.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, LOUIS
JOSEPH ARSENE BRUN, of Paris, in the Empire of France, Merchant, send
greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the First day of January, in the year of our Lord
One thousand eight hundred and fifty-eight, in the twenty-first year of Her
reign, did, for Herself, Her heirs and successors, give and grant unto me, the
said Louis Joseph Arsène Brun, Her special licence that I, the said Louis
Joseph Arsène Brun, my executors, administrators, and assigns, or such
others as I, the said Louis Joseph Arsène Brun, my executors, administrators,
and assigns, should at any time agree with, and no others, from time to time
and at all times thereafter during the term therein expressed, should and
lawfully might make, use, exercise, and vend, within the United Kingdom of
Great Britain and Ireland, the Channel Islands, and Isle of Man, an Invention
for "IMPROVEMENTS IN INSTRUMENTS FOR MEASURING ANGLES, APPLICABLE TO
NAUTICAL AND OTHER PURPOSES," upon the condition (amongst others) that I,
the said Louis Joseph Arsène Brun, my executors..or administrators, 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

page_text: 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 Louis Joseph Arsène Brun, do hereby
declare the nature of my said Invention, and in what manner the same is to
be performed, to be particularly described and ascertained in and by the
following statement, reference being had to the Sheet of Drawings hereunto
annexed, and to the letters and figures marked thereon (that is to say) :-
My Invention relates to a compensating protractor, which allows of at once
placing on paper (flat or hydrographical maps, topographical surveys, plans,
&c.,) with regard to the meridian, the angles or directions measured in nature
with a magnetic needle or a compass in reference to the magnetic meridian,
and that without taking into account the variation or declination of the mag-
netic needle at each operation. Thus, and to be more intelligible, if it be a
topographical compass, this new protractor allows of the tracing immediately
on paper, and without other aid than that of the meridians already marked
thereon, the projection itself of directions seen in nature; if it be a mariner's
compass it allows of the tracing at once, and without calculation, either the
direction travelled, or a bearing taken, &c. In a word, the compensating
protractor, in which the graduation is, at the will of the operator, moveable or
fixed with regard to the true line. It is composed of, first, a first transparent
plate or table (horn, glass, &c.), two sides a, b, & c, d, Fig. 1, of which (which
I call rules) are exactly parallel to each other, and also to a line e, f, traced on
the plate (which I call the true line). This true line is made near the middle
of the table, Fig. 1 of the Drawings annexed, if the second plate or limb
herein-after referred to is circular; it is, on the contrary, near one of the rules,
Fig. 2, if the limb is semicircular, or when it is desired to employ a circular
limb of greater diameter than the table. The two rules or only one of them
may be furnished with a metal or wooden border, either moveable or not, as
shown in Fig. 2, but this is not of great utility. The table is besides pierced
with two holes g, h, Figs. 1, 2, 6, 7, & 8, or it may be a groove or part cut
out (Fig. 3), intended to receive screws, Fig. 5, the heads of which (which are
very flat) are placed below the table, and on which a nut is screwed, Fig. 4,
the pressure of which suffices to hold and fix the limb herein-after referred to
on the table. These holes are so arranged that the centre of the limb held by
the screws may be placed on the true line. Although the arrangement of
grooves, Fig. 3, seems advantageous at first, because it allows the using limbs
of different diameter on a single table, yet I prefer the system of holes,
because the screws are less liable to be lost, and also because it is easier to
work the limb. Secondly, a second plate (the limb), which is also transparent;

page_text: it may be circular or semicircular, and is graduated. The limb is so placed
on the table that its centre is on the true line, then by making it turn on the
table, any graduation desired can be made to coincide with the true line, and
then the screws are tightened. By this means a protractor is produced, the
zero radius of which is inclined to the rule at the angle required.
All modes of graduation at present in use may be applied to this instrument,
but when it is more particularly intended for marine purposes it is well to
adopt a graduation exactly analogous to that of the mariner's compass, the
mariner's card included, the north line of which coincides with the zero radius.
The limb may be circular and of smaller diameter than the table, Fig. 6; or
of greater diameter than the table, Fig. 7; or lastly, semicircular, as at Fig. 8.
In these three Figures 6, 7, 8, the zero radius of the limb is supposed to be
superposed on the true line of the instrument. It is advantageous to leave a
kind of margin, about an inch or an inch and a half wide, round the whole
circumference of the limb; this margin prevents the nuts resting on and
injuring the graduations. This arrangement is represented at Fig. 9.
A number of modifications can be made in this instrument. Thus, if
thought advisable, a vernier scale can be added at the right and left of the
true line to show with greater or less approximation the fractions of the last
subdivisions of the limb. The instrument may be constructed of copper or
any other metal, care being taken to render visible the centre of the limb,
Fig. 10. In this case the limb may be submitted to the action of adjusting
screws, which will render its movements extremely slow.. Lastly, the form
may easily be varied, as seen in the instrument, represented at Fig. 10, in
which the dark tint indicates the limb, and the yellow indicates the table
and rule; it is also evident that in this same Figure the true line is the
diameter e, f, parallel to the rule a, b.
The protractor of my Invention is, in fact, nothing but a goniometer,
because it serves to measure and trace angles on paper, and, like all gonio-
meters, it can be used with either a fixed or moveable limb. The preceding
description has reference to the protractor, considered only as a goniometer,
having a moveable limb; what follows relates exclusively to the compensating
protractor, considered as a goniometer, having a fixed limb, so that the
instrument which I am about to describe, properly speaking, is simply a
modification of the protractor described above.
The compensating protractor having a fixed limb consists, first, of a plate
which is generally transparent and circular, or semicircular and graduated,
which is called the limb (Figs. 11 & 12). Any mode of graduating at present
in use may be applied thereto.

page_text: Secondly, of a hand or indicator (Figs. 13 & 14) having a hollow centre,
which enters with a little friction in a socket X (Figs. 11, 12, 15, & 16),
which socket is also hollow, in order to admit of the centre C of the instru-
.ment being seen. This socket is fixed on the. limb by screws, rivets, or any
other means; the needle can therefore be turned at will by the operator
round the centre C of the instrument, and it can be stopped and fixed on any
graduation by means of a nut V (Figs. 11, 12, 15, & 16), by the simple
pressure which it exerts against the limb. The socket X (Figs. 11, 12, 15,
.& 16) has a screw on the exterior, as seen in Figs. 15 & 16, the nut V on
the contrary is screwed in the interior, as seen in Figs. 15 & 16. A trans-
parent limb is employed to facilitate the use of the instrument that is to trace
the point in navigation, but it could also be of metal, and the centre would
then be left apparent according to a plan analogous to that at present in use
for ordinary metal protractors. It is also for the sake of convenience that the
centre is left open to view, as the needle could turn just as well on a solid
metal axis placed at the centre of the instrument as on a hollow socket, as
described.
This new mode of mounting is also applicable to the compensating pro-
tractor having a moveable limb, by hollowing the limb at the centre exactly
as described with reference to the needle, and in this case the two screws
serving to fix the limb on the plate at the will of the operator is dispensed
with.
In witness whereof, I, the said Louis Joseph Arsène Brun, have here-
unto set my hand and seal, this Fifteenth day of June, One thousand
eight hundred and fifty-eight.
זוזזתבת
L. J. A. BRUN. (..)