Improvements in Range Finders.
Year: 1899

page_text: Date of Application, 11th Mar., 1899
Complete Specification Left, 11th Dec., 1899-Accepted, 27th Jan., 1900
Improvements in Range Finders.
T, ANDREW BETTS BROWN, Engineer, of Rosebank Engineering Works, in the
County of the City of Edinburgh, North Britain, do hereby declare the nature
of this invention to be as follows:-
This invention relates to a rapid method of ascertaining distances. This 1
do by the adaptation of an ordinary sextant with a particular form of gearing
to measure angles subtended by objects at a distance the heights of which are
previously known or assumed, and the reading off on a graduated dial plate the
distances corresponding to the angles so found.
In order to make this instrument suitable as a range or distance finder, which
consists in the accurate measure of extremely small angles (as those subtended
by short objects at comparatively long distances or ranges) and also to enable the
result to be represented on a sufficiently large index plate, the following form of
gearing or mechanism is introduced.
The angular rotary motion given to the movable reflecting mirror is produced
by means of a cam of suitable form revolving on a centre. This cam is driven
by the index bar and by a motion of the same the various points of contact of
the cam on a bar pivoted to the frame carrying the mirror produce a uniformly
angular motion of the reflecting mirror.
In order to insure that the surfaces of the bar and cam are always in contact,
a spring is introduced the one end being fixed to the rotating mirror arm and
the other end to the frame of the sextant.
Any required ratio of the angle traversed by reflecting mirror to that of the
index arm to suit the degree of accuracy of reading and the extent of range or
distances required may be made by alteration of the form of the cam.
GRADUATION OF INDEX PLATE.
The index plate over which the index arm travels is graduated in the follow-
ing manner-
Firstly, the plate is lined off by a line drawn radially outwards from the centre
which may be called the "height" line. Along the "height" line a number
of points are chosen and plotted at proportionate distances from the centre,
representing a suitable number of heights of objects. Through these various
points concentric circular arcs are traced out about the centre. These ares may
be called the range ** lines.
Along one of the range lines I obtain a suitable number of points which I
designate as ranges or distances and in order to obtain these I assume both a
suitable range of an object and its height, and from these data I compute the
angle subtended by calculation. Having obtained this angle and increased it
by the angular ratio of the reflecting mirror to that of the index arm, I now
sweep the index arm through this calculated angle and where it cuts the corre-
sponding range "line I mark that position as the range or distance from
which the angle was calculated. I continue this process along the "range"
line until. I obtain the sufficient number of ranges required for that height of
::

page_text: object. I then in a similar manner obtain other series of points along the
various ares or range" lines corresponding to the various heights of objects
whose ranges I require.
Having now obtained a suitable number of range points corresponding to a
sufficiently varied number of heights of objects, I then join these points by lines
representing a series of curves, from which in a rapid manner the range of a
given object corresponding to the angle so taken can be read off, the heights of
the said object being either known or assumed beforehand. Each of these curves
now represents the range of a series of objects of different heights (or angles
subtended by different heights of objects at the same range).
A sliding pointer is fitted to the index bar to be set to the supposed or assumed
height of the object whose range is required. A clamping screw is also fitted
to the end of the index bar in order to fix the position of the bar after an angle
has been taken.
The size of the index plate can be made to suit the variety of heights of objects
to be represented.
I, ANDREW BETTS BROWN, Engineer, of Rosebank Engineering Works, in the
County of the City of Edinburgh, North Britain, do hereby declare the nature,
of this invention and in what manner the same is to be performed, to be parti-]
cularly described and ascertained in and by the following statement:-
This invention relates to a rapid method of ascertaining distances. This I
do by the adaptation of an ordinary sextant with a particular form of gearing
to measure angles subtended by objects at a distance the heights of which are
previously known or assumed, and the reading off on a graduated dial plate the
distances corresponding to the angles so found.
In order to make this instrument suitable as a range or distance finder, which
consists in the accurate measure of extremely small angles (as these subtended
by short objects at comparatively long distances or ranges) and also to enable the
result to be represented on a sufficiently large index plate, the following form of
gearing or mechanism is introduced.
The angular rotary motion given to the movable reflecting mirror is produced
by means of a cam of suitable form revolving on a centre. This cam is driven
by the index bar and by a motion of the same the various points of contact of
the cam on a bar pivoted to the frame carrying the mirror produce a uniformly
angular motion of the reflecting mirror.
In order to insure that the surface of the bar and cam are always in contact
a spring is introduced the one end being fixed to the rotating mirror arm and
the other end to the frame of the sextant.
Any required ratio of the angle traversed by reflecting mirror to that of the
index arm to suit the degree of accuracy of reading and the extent of range or
distances required may be made by alteration of the form of the cam.
In order that my invention may be properly understood and readily carried
into effect, I have hereunto appended one sheet of drawings.

page_text: The index handle is shown at A which sweeps round the dial plate B upon
which there are a number of curves drawn to indicate the range. On the index
bar A there is the sliding pointer C which is set to a scale marked radially on
the dial plate indicating the height of the masts of a ship and ranging from 40
up to 160 feet.
The index bar A is attached to a spiral cam D with a worm E
fixed on the radial of the index bar A and operating on a worm wheel segment F
for the purpose of giving a micrometer adjustment. Resting on this cam is a
piece capable of adjustment by sliding block with a lever H. On this lever is
mounted a mirror I which reflects the object in a stationary mirror J which has
the usual adjustments as in the ordinary sextant.
At K there is a pedestal and ring mounted, into which can be inserted a
telescope.
The mirror I has fitted to it a compression spring L which keeps the bearing
piece G firmly against the surface of the cam.
The angular movement of the index bar A is 80 times as much as that of
the mirror I and the curved lines on the index plate B are calculated for such a
proportion.
GRADUATION OF INDEX PLATE.
The index plate over which the index arm travels is graduated in the follow-
ing manner:-
Firstly, the plate is lined off by a line drawn radially outwards from the centre
which may be called the "height" line. Along the "height" line a number
of points are chosen and slotted at proportionate distances from the centre,
representing a suitable number of heights of objects. Through these various
points concentric circular ares are traced out about the centre. These ares may
be called the " range lines.
Along one of the range lines I obtain a suitable number of points which I
designate as ranges or distances and in order to obtain these I assume both a
suitable range of an object and its height, and from these data I compute the
angle subtended by calculation. Having obtained this angle and increased it
by the angular ratio of the reflecting mirror to that of the index arm, I now
sweep the index arm through this calculated angle and where it cuts the corre
sponding rangeline I mark that position as the range or distance from
which the angle was calculated. I; continue this process along the " range
line until I obtain the sufficient number of ranges required for that height of
object. I then in a similar manner obtain other series of points along the
various ares or
range lines corresponding to the various heights of objects
whose ranges I require.
"
39
Having now obtained a suitable number of range points corresponding to a
sufficiently varied number of heights of objects, I then join these points by lines
representing a series of curves, from which in a rapid manner the range of a
given object corresponding to the angle so taken can be read off, the heights of
the said object being either known or assumed beforehand. Each of these curves
now represents the range of a series of objects of different heights (or angles
subtended by different heights of objects at the same range).
A sliding pointer is fitted to the index bar to be set to the supposed or assumed
height of the object whose range is required. A clamping screw is also fiited
to the end of the index bar in order to fix the position of the bar after an angle
has been taken.
The size of the index plate can be made to suit the variety of heights of objects
to be represented.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed, I declare that what
I claim is
1. The range finder, substantially as herein described and illustrated.

page_text: 2. The spiral cam mechanism by which the angular motion of the mirror I is
multiplied, substantially as herein described and illustrated.
Dated this 21st day of November 1899.
BOTTOMLEY & LIDDLE,
154, St. Vincent Street, Glasgow, Applicant's Patent Agents.