Improvements in and connected with Range Finders.
Year: 1893

page_text: Date of Application, 7th Jan., 1893
Complete Specification Left, 5th June, 1893-Accepted, 8th July, 1893
PROVISIONAL SPECIFICATION.
Improvements in and connected with Range Finders.
I, ARTHUR OCTAVIUS GREEN, of Brompton Barracks, Chatham, in the County
of Kent, Major in the Corps of Royal Engineers, do hereby declare the nature of
this invention to be as follows:-
The invention relates to improvements in and connected with range finders,
whereby great accuracy of observation is obtained, and whereby the instrument can
be readily fixed to and removed from an ordinary field-glass.
This instrument is based upon the well known principle of double reflection from
two plane mirrors. It consists of two central fixed mirrors, placed with their
silvered sides back to back, and their reflecting surfaces outwards, and of two other
mirrors, one on each side of the central pair, which are capable of adjustment by
means of a key to any required angles, which shall give a fixed ratio between a
measured base and the distance of the object, the range of which is required to be
known.
The method of its adjustment is as follows, reference being had to the accom-
panying diagram.
O being a known point the distance of which from A is accurately known (say
2000 yards), a line B A D is laid out accurately at right angles to O A, and a
distance mark either found or placed at D, at about the same distance from A,
that O is from A. No. 1 mirror, being one of the outer mirrors, is now made to
reflect the object O on to the point D by means of the adjusting screw, and these
mirrors will now always enable a right angle to be set off, (a right angle has been
selected as being a generally useful angle).
-
A distance AB, which bears a fixed ratio to the required range A O-the ratio
selected is and in this case would be 2000.
40 yards, snow carefully measured
in the line DA B, and at the point B, by means of the adjusting screw, No. 2
(outer) mirror is made to reflect the object O again on to the point D, i.e., to read
the angle OBA of a triangle in which the angle OA B is a right angle and the
length of the side A B is known.
It follows, therefore, that these mirrors, when once adjusted, will always enable
one to set off the angles at the two ends of a measurable base, which itself will
always bear a fixed ratio to the distance of the object required, provided the range
does not exceed the limit of distance for which the instrument was originally
adjusted.
An effective arrangement of means for adjusting the angle of the outer mirrors is
as follows
The mirror frame has fixed therein a spring, one end of which is fixed to the
frame whilst the other carries clips to hold the outer edge of the mirror, and near
to the clips a screw stud, fixed to the spring and acted upon by a nut, causes the
clips to draw the outer end of the mirror down to fixed stops. The inner end of the
mirror rests upon the end of a screw and is pressed against the latter by a spring;
this latter screw works in a thread made in the mirror frame, and it is shaped at its
outer end to receive a key by which it can be turned to effect the adjustment of
the angle of the mirror.
The instrument is provided at the angle of the mirrors with a hinged arm which
is capable of ready connection and disconnection with an arm carried by a divided
ring provided with a screw connection at the joint to enable the said ring to be
readily fixed to the sun-shade of a field-glass.
The adjustments once made previous to issue by the instrument maker, the
instrument will not require any further adjustment.

page_text: The name by which this instrument will be known is "Green's Broad Arrow
Telemeter" for infantry purposes.
Dotal Tanuary 7th 1902
ARTHUR O. GREEN,
By Harris & Mills,
23, Southampton Buildings, London, W.C., Agents.
COMPLETE SPECIFICATION.
Improvements in and connected with Range Finders.
I, ARTHUR OCTAVIUS GREEN, of Brompton Barracks, Chatham, in the County
of Kent, Major in the Corps of Royal Engineers, do hereby declare the nature of
this 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 accompanying drawings and to the figures and letters marked thereon:--
The invention relates to improvements in and connected with range-finders
whereby great accuracy of observation is obtained, and whereby the instrument can
be readily fixed to and removed from an ordinary field-glass.
My invention is illustrated in the accompanying drawings, in which
Figure 1 is a perspective view showing the instrument attached to a field glass.
Figure 2 is a sectional edge view of the instrument separately,
Figure 3 is an inner face view showing one of the outer mirrors and
Figure 4 is a diagram for use in explaining the method of adjusting the
instrument.
The instrument is based upon the well known principle of double reflection from
two plane mirrors. It consists of a three legged frame a having two central rigidly
fixed mirrors placed with their silvered sides back to back and their reflecting
surfaces outwards, and two other mirrors c c mounted in the outer arms of the frame
with their reflecting surfaces opposite to and one on each side of the central pair.
These two mirrors e c are capable of adjustment to a certain range of angle by
means of adjusting screws de which shall give a fixed ratio between a measured
base and the distance of the object the range of which is required to be known.
An effective arrangement of means for adjusting the angle of these outer mirrors is
as follows:-
Each of the outer arms of the mirror frame has fixed therein a plate or spring f,
one end of which is fixed to the frame a whilst the other carries clips to hold the
outer edge of the mirror c, and a screw stud d fixed to the plate or spring and
acted upon by a nut d', causes the clips to draw the outer end of the mirror c down
to fixed studs or stops g. The inner end of the mirror is pressed by the end of a
screw e firmly against a strong spring i; this latter screw e works in a thread made
in the mirror frame and it is shaped at its outer end to receive a key by which it
can be turned to effect the adjustment of the angle of the mirror. Thus a con-
siderable amount of movement can be given to the mirror itself about one end
without fear of the adjustment being altered when once made without the use of the
proper key.
The instrument is provided at the angle of the mirrors with an arm which
terminates in a small ball capable of ready connection and disconnection by a
screw with a forked arm & carried by a strap as shown or by a divided ring
provided with a screw connection at the joint to enable the said attachment to be
readily fixed to the sunshade of a telescope or field-glass.
The outer cases are numbered 1, 2, respectively, on the outside, and the method
of adjustment is as follows, reference being had to the diagram shown in Figure 4.
O being a point, the distance of which from A is accurately known (say
2,000 yards), a line B A D is laid out accurately at right angles to OA with a
theodolite or otherwise, and a distance mark either found or placed at D at about
the same distance from A that O is from A. By means of the adjusting screw e,

page_text: No. 1 mirror is now made to reflect the object O from the opposite central mirror
on to the point D which is seen by direct vision either above or below the mirror
case, and this pair of mirrors will now always enable a right angle to be set off (a
right angle has been selected as being a generally useful angle).
A distance A. B, which bears a fixed ratio to the known range A O-the
ratio selected is 36-and in this case would be 2000 = 40 yards, is now carefully
measured in the line DA B, and at the point B, by means of the adjusting screw e,
No. 2 (outer) mirror is made to reflect the object O again on the point D, i.e., to
read the angle O BA of a triangle in which the angle O A B is a right angle and
the length of the side A B is known.
It follows, therefore, that these mirrors, when once adjusted, will enable one to
set off the angles at the two ends of a measurable base, which itself will always
bear a fixed ratio to the distance of the object required, provided the range does
not exceed the limit of distance for which the instrument was originally adjusted,
which in this case has been taken to be 2,000 yards. When once adjusted previous
to issue by the maker, the instrument will not require any further adjustment
and the adjusting screw can be cemented, if necessary, so as to be absolutely
immovable.
The method of using the instrument is as follows:-
Holding the instrument in the right hand, between the forefinger and thumb, up
to the right eye, turn No. I mirror case in the direction of the eye, and glance over
the top of the central case, or underneath if annoyed by glare, at the object of
which it is desired to find the range. A large field of view is now seen in the
central mirror to the left hand, in which some distance mark may be selected with
which to bring the object into coincidence by either moving backwards or forwards.
Should, however, no favorable object present itself in the field of view to the left,
the instrument may be turned upside down, held in the left hand with No. 1 mirror
still towards the right eye, and an object favorable for the purpose sought in the
field of view to the right. This operation can be performed with great rapidity,
and after a very little practice favorable distance points can be quickly picked up.
Now turn towards the selected distance point, and make accurate contact by
reflecting the object on to the distance point, as seen by direct vision either over
the top or underneath the instrument frame, by moving towards or back from the
distance point as the case may be. A little practice will soon show which way to
move, according as the reflected object falls to the right or the left of the distance
point, and the instrument is held with the mirrors either towards the right or the left.
If the mirrors are turned towards the left hand and the reflected object is seen to
the left of the distance point, or mirrors to the right, and reflected object to the
right, move back; if the mirrors are to the left, and reflected object to the right
of the distance point, or vice versa, move forward. Leave a mark, and for this I
would recommend a white stick with pointed ferrule, or a ramrod, sticking up in the
ground between the place where your feet were, and run back to rather more than
what you think your base will be; align yourself as accurately as possible by
means of the stick and distance point, and then reflect the object by means of
No. 2 mirror on to the distance point, completing the contact by moving inwards,
taking care to keep on the alignment. Having completed the contact satisfactorily,
the base thus found may be either paced or measured with a tape, and its
distance will be of the required range. Suppose the base measured 35 paces
or yards, the range would be 35 × 100: = 1,750 yards, a sum which does not require
any great mental arithmetic.
=
The above description makes the operation appear a very lengthy affair, but a
range can be taken in less than a minute with only one observer. It is a little
longer when using the instrument in combination with a field-glass or telescope for
long ranges suitable for artillery, but for most infantry ranges it would be
preferable to use it simply by itself, unless the atmosphere is misty or dull, or a
person is short-sighted, when, of course, the glasses enable much better contacts to
be made.

page_text: The field-glass attachment enables the central mirrors to be brought in succession
into more or less of a line with the optical axis of any glass, the bar being
strapped firmly to the sunshade of the glass, and by rotating the range-finder
slightly, images can be brought into contact in the same vertical plane, even when
they are at considerable differences of altitude, which is, of course, of very great
practical importance.
All the above instructions refer to the single instrument; it is, however, capable
of giving very rapid and accurate results for long ranges when used in combina-
tion with another exactly similar instrument manipulated by a second observer.
In this case observer A, making use of No. 1 mirror, catches the reflection of
the object, and motions observer B to the right or left with his disengaged hand,
until B's eye, as seen direct over the top of the instrument, is in contact with
the reflected object. B, making use of No. 2 mirror, now advances or retires on
this line until he makes contact between the reflected object and A's eye, being in
the meantime kept on the true alignment by A. The distance between the two
observers when both have contact is th of the range and can be paced or
measured. If the range is under 1,000 yards it is better for both observers to use
No 2 mirror, in which case the base is th of the range, the angles laid off being
those at the base of an isosceles triangle, in which the ratio of base to range is
1 to 25.
The name by which this instrument will be known is "Green's Broad Arrow
Range Finder."
Having now particularly described and ascertained the nature of my said inven-
tion, and in what manner the same is to be performed, I declare that what I
claim is :-
1. The improved range-finder constructed substantially as herein shown and
described.
2. The improved range-finder and method of connecting the same with a telescope
or field-glass, substantially as herein shown and described.
3. A range-finder consisting of a three-armed frame having two mirrors rigidly
fixed back to back in the central arm and an angularly adjustable mirror in each
outer arm facing a mirror of the central arm, substantially as herein shown and
described.
Dated this 5th day of June 1902
UREEN, MAJOR IV. M.,
By Harris & Mills,
23, Southampton Buildings, London, W.C., Agents.