I- PROVEMENTS IN QUADRANTS, SEXTANTS, AND OTHER SIMILAR INSTRUMENTS
Year: 1857

page_text: in the ounty of Middlesex, and of 160, Buchanan Strect, in the
City of Glasgow, North Britain, Gentleman, for the Invention of "I-
PROVEMENTS IN QUADRANTS, SEXTANTS, AND OTHER SIMILAR INSTRUMENTS."-
A communication from James C. Lanc, of Brooklyn, in the State of
New York, in the United States of America.
Sealed the 23rd September 1857, and dated the 15th June 1857.
PROVISIONAL SPECIFICATION left by the said John Henry Johnson at
the Office of the Commissioners of Patents, with his Petition, on the
15th June 1857.
I, JOHN HENRY JOHNSON, of 47, Lincoln's Inn Fields, in the County of
Middlesex, and of 166, Buchanan Street, in the City of Glasgow, North
Britain, Gentleman, do hereby declare the nature of the said Invention for
"IMPROVEMENTS IN QUADRANTS, SEXTANTS, AND OTHER SIMILAR INSTRUMENTS," a
communication from James C. Lane, of Brooklyn, in the State of New York,
in the United States of America, to be as follows:-
This Invention relates to a peculiar adaptation of parts to quadrants,
sextants, and other instruments of a like nature, whereby an artificial horizon.
or zenith is obtained for the purpose of measuring the altitude of the sun,
and for any purpose to which quadrants or sextants are applied; and
observations may be made at times when the real horizon is obscured or
obstructed.
These improvements consist in the application and use of a constantly.
horizontal mirror in connection with the eye piece and horizon glass, and

page_text: so arranged that the inclination of the latter can be read directly upon a
segmental arc, giving the complement of the angle formed by the sun or any
other object and the zenith. A constantly vertical mirror may also be used
in connection with the eye piece, horizon glass, cross bair lines or their
equivalents, interposed between the said eye piece and vertical mirror; and an
index glass, whereby an artificial horizon can be readily obtained, and the
altitude of the sun or of any other object can be read upon a segmental are,
giving the angle of the sun or any other object with the horizon......
SPECIFICATION in pursuance of the conditions of the Letters Patent, filed
by the said John Henry Johnson in the Great Seal Patent Office on
the 15th December 1857.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, JOHN HENRY
JOHNSON, of 47, Lincoln's Inn Fields, in the County of Middlesex, and of 166,
Buchanan Strect, in the City of Glasgow, North Britain, Gentleman, send
greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Fifteenth day of June, in the year of our Lord Que
thousand cight hundred and fifty-seven, in the twentieth year of Her reign,
did, for Herself, Her heirs and successors, give, and grant unto me, the said
John Henry Johnson, Her special license that I, the said John Henry
Johnson, my executors, administrators, and assigns, or such others as I, the said
John Henry Johnson, my executors, administrators, or 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
QUADRANTS, SEXTANTS, AND OTHER SIMILAR INSTRUMENTS," a communication
from James C. Lane, of Brooklyn, in the State of New York, in the United
States of America, upon the condition (amongst others) that I, the said
John Henry Johnson, by an instrument in writing under
hand and seal
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 J, the said John Henry Johnson, do hereby declare
the nature of the said Invention, and in what manner the same is to be per-

page_text: formed, to be particularly described and ascertained in and by the following
statement, reference being had to the accompanying Drawings, and to the
letters and figures marked thereon, that is to say:-
The said Invention relates to a peculiar adaptation of parts to quadrants,
sextants, and other instruments of a like nature, whereby an artificial horizon
is obtained for the purpose of measuring the altitude of the sun, and for any
purpose to which quadrants or sextants are applied; and observations may be
made at times when the real horizon is obscured or obstructed.
These improvements consist in the application and use of a constantly
horizontal mirror in connection with the eye piece and horizon glass, and so
arranged that the inclination of the latter can be read directly upon a
segmental arc, giving the complement of the angle formed by the sun or any
other object and the zenith. A constantly vertical mirror may also be used
in connection with the eye piece, horizon glass, cross hair lines or their equi
valents, interposed between the said eye piece and vertical mirror; and an
index glass, whereby an artificial horizon can be readily obtained, and the
altitude of the sun or of any other object can be read upon a segmental arc,
giving the angle of the sun or any other object, with the horizon.
And in order that the said Invention may be fully understood I shall now
proceed more particularly to describe the same, and for that purpose I shall
refer to the several Figures on the Sheet of Drawings hereunto annexed; the
samic letters of reference indicate corresponding parts thoughout all the
Figures.
:
:
Figure 1 of the Drawings represents a front view;
Figure 3, a plan of my improved instrument; and
sectional detail of the same.
Figure 2, a back-view;
Figure 4, an enlarged
A represents a loaded cup, supported on the end of a bracket by means of
gimbols or compass bearings, in such a manner that it will remain at rest in
but one position.
:
The level top of the cup contains a reflecting surface or mirror B, which
is removable at pleasure, to receive in its place a vertical mirror. The mirror
may be so arranged as to pivot upon two bearings, & to be adjustable either
for the horizontal or vertical position.
The bracket C is attached to a portion of that limb of the quadrant which
carries the horizon glass. The loaded cup is adjustable in height by means of
a screw D, working in a cylindrical box nut E. The latter is armed with
a pin or stud, which, moving in a spiral-shaped slot F of the socket G, acts
as a guide for the proper adjustment of the mirror.
It is obvious that, when the horizontal mirror is used, it should occupy such

page_text: a position that the visual ray shall pass from the eye piece through the
horizontal centre line of the horizon glass, & strike the centre line of the
mirror, which is parallel with the horizontal centro line of the horizon glass.
But when the vertical mirror is used it is not necessary that the visual ray,
passing through the eye piece and the horizon glass, should strike the centre
of the mirror, the principal object is, that the inage of the horizontal cross
hair shall be reflected back, in coincidence with the real cross hair. It is
therefore important to adjust the vertical mirror, so that it shall occupy a
convenient position to reflect the eye picce. The spiral slot F effects this
object by giving the required position at a certain point of elevation of the
mirror. Between the eye piece and the mirror is situated a frame H, con-
taining cross hairs at right angles to each other. I prefer to use a glass with
colored lines across it, on account of the hygrometrical state of the atmosphere
rendering hairs unsteady. In the ordinary method of measuring the altitude
of the sun the real horizon is required, in order to have the reflected image of
the sun to coincide with it.
By using the apparatus herein described, I can dispense with the real
horizon, which is very important when it is obscured or obstructed. The real
horizon is obtained artificially when the hair lines which are interposed
between the eye piece and the perpendicular mirror are so reflected back that
the reflected image of the hair lines coincides with the real hair lines.
When the horizontal mirror is used, the altitude of the sun can be measured
directly by obtaining the complement of the angle the arm makes into the
zenith. This is done by causing to concide both the reflection of the sun
from the constantly horizontal mirror and the horizon glass, which, of course, is
placed in a position parrallel with the mirror and upon the line of the reflected
The back arc J is so graduated that the complement of the angle the
sun is making with the zenith is read directly from it. It will be perceived
that the index glass is not used with the horizontal mirror.
ray.
Having now described and particularly ascertained the nature of the said
Invention, and the manner in which the same is or may be used or carried
into effect, I would observe, in conclusion, that I do not confine or restrict
myself to the precise details or arrangements which I have had occasion to
describe or refer to, as many variations may be made therefrom without
deviating from the principles or main features of the said Invention; but what
I consider to be novel and original, and therefore claim as the Invention secured
to me by the herein-before in part recited Letters Patent, is,-
First, the application and use to and in quadrants, sextants, and other
instruments of a similar nature for taking altitudes, of a constantly horizontal

page_text: reflecting surface or mirror, in such manner that the line of vision, passing
through the eye piece and horizon glass, shall striko the intersection of the
lines of rotation of the said mirror, for the purpose herein-before described.
Second, the application and use to and in quadrants, sextants, and other
instruments of a similar nature, of a constantly perpendicular reflecting surface
or mirror, in such manner that the line of vision, passing through the eye piece
and horizon glass, shall strike the intersection of two perpendicular planes
passing through lines parallel with the lines of rotation of the said mirror, for
the purpose herein-before described.
Third, the interposing between the eye piece and the perpendicular or
horizontal mirror, herein-before referred to, of a frame containing cross hairs or
their equivalents, for the purpose herein-before described.
In witness whereof, I, the said John Henry Johnson, have hereunto set
my hand and seal, the Fifteenth day of December, One thousand
eight hundred and fifty-seven.
J. HENRY JOHNSON. (L.S.)