Improvements in Ascertaining the Distances of Inaccessible or other Objects, and in Apparatus employed therein.
Year: 1892

page_text: Date of Application, 23rd Feb., 1892
Complete Specification Left, 22nd Nov., 1892-Accepted, 31st Dec., 1892
PROVISIONAL SPECIFICATION.
Improvements in Ascertaining the Distances of Inaccessible or other
Objects, and in Apparatus employed therein.
I, GEORGE HAMILTON FENNER of 14 The Avenue, Bedford Park, Acton in the
County of Middlesex, Bachelor of Arts and Military Tutor, do hereby declare the
nature of this invention to be as follows:-
Various methods of range finding have been suggested, some being based on
the employment of a mechanical base capable of being carried from place to place,
others on the calculation of a base fixed in direction but not transportable with the
apparatus.
In either case the direction is substantially a fixed one relatively to the range.
According to my invention I can lay down a base in any suitable or convenient
direction relatively to the direction of the range sought without material
restriction.
In carrying out my invention having selected a sufficiently well defined point in
the object whose range is sought I choose another sufficiently well defined object in
any convenient direction in order to align thereupon the base by means of which
the range is ultimately measured.
In laying down a base in this manner I am not restricted to the choice of an
object in any particular or predetermined direction.
The instrument, the subject of the invention, consists of a metallic box preferably
in the shape of a quadrant or quarter circle inside which are arranged mirrors say
two in number as in a sextant, one, fixed, being formed as half mirror half plain
glass, the other moveable, being a complete mirror.
To the moveable mirror is attached a toothed wheel, sector or equivalent part to
which is geared a second toothed wheel or equivalent part of one half the diameter
to the spindle of the latter wheel is fixed a straight lever with bevelled edge which
traverses a metal disc through an arc of about 95° to 100°. On the disc are traced
portions of the circumferences of circles each circle passing through the centre on
which the lever rotates and described so that its diameter corresponds with the
position of the edge of the lever when the mirrors show an angle of 90°.
The diameters of the circles are respectively those lengths on which are
represented the maximum multiples of the base when the base is respectively
1. 2. 3. 4. 5. 6. 7. 8. 9. 10 units.
The bevelled edge is divided into convenient equal divisions.
The circumferences of the circles are numbered 1 to 10.
The lever and consequently the moveable mirror are made capable of being
moved through a small are after an observation has been taken either by means of a
tangent screw, a stop or suitable equivalent means capable of being regulated
according to requirement by a micrometer screw or otherwise.
The instrument is used as follows. Any well defined object is chosen making a
convenient angle (preferably not less than 30°) with the direction of the object
whose range is required, the angle between these two directions is then recorded on
the instrument by moving the index mirror. The mirror and lever are then
adjusted to an angle differing from that angle by some small amount such for
instance as from 45' to 2° 30' (forty-five minutes to two degrees thirty minutes) by
the means mentioned above, or such adjustment may be made by means of another
pair of mirrors giving the desired angle.
The observer advances in the direction of the second object until this increased
angle is given by the mirrors. The base i.e. the distance between the first
and this last point of observation is ascertained and the corresponding range is read

page_text: off the lever. Thus, suppose the base is 75 yards the division on the lever cut by
the circle 7 is read and multiplied by 10 then that cut by the circle 5 and the two
are added. If there is a decimal fraction in the base it can be similarly included,
or intermediate circles may be drawn to give readings intermediate to those given
by the circles numbered 1 to 10.
If desirable a fixed base may be used in which case it will be necessary to vary
the difference angle, the same readings will be used provided the base be first
multiplied by the fraction shown on the micrometer screw.
Amongst the advantages attendant upon the employment of the foregoing method
and apparatus is the fact that the base increases with increase of the length of the
range obviating thereby increased liability to error that would otherwise arise.
Dated the 23rd day of February 1892.
WM. BROOKES & SON,
55 & 56, Chancery Lane, London, Agents for the Applicant.
COMPLETE SPECIFICATION.
Improvements in Ascertaining the Distances of Inaccessible or other
Objects, and in Apparatus employed therein.
I GEORGE HAMILTON FENNER of 14 The Avenue, Bedford Park, Acton in the
County of Middlesex, Bachelor of Arts and Military Tutor 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 :-
Various methods of range finding have been suggested, some being based on
the employment of a mechanical base capable of being carried from place to place,
others on the calculation of a base fixed in direction but not transportable with
the apparatus.
In either case the direction is substantially a fixed one relatively to the range.
According to my invention I can lay down a base in any suitable or con-
venient dirction relatively to the direction of the range sought without material
restriction.
In carrying out my invention having selected a sufficiently well defined point in
the object whose range is sought I choose another sufficiently well defined object
in any convenient direction in order to align thereupon the base by means of
which the range is ultimately measured.
In laying down a base in this manner I am not restricted to the choice of any
object in any particular or predetermined direction.
The instrument the subject of the invention, consists of a metallic box prefer-
ably in the shape of a quadrant or quarter circle sextant, circle, square or other
convenient form inside which are arranged mirrors say two in number as in a
sextant, one, fixed being formed as half mirror half plain glass, the other moveable,
being a complete mirror.
To the moveable mirror is attached a toothed wheel, sector or equivalent part
to which is geared a second toothed wheel or equivalent part of one half of the
diameter to the spindle of the latter wheel is fixed a straight lever with bevelled
edge which traverses a metal disc through an arc of about 95° to 100°.
On the disc are traced portions of the circumferences of circles_each_circle
passing through the center on which the lever rotates and described so that its
diameter corresponds with the position of the edge of the lever when the mirrors
show an angle of 90°.
The diameters of the circles are respectively those lengths on which are repre-
sented the maximum multiples of the base when the base is respectively 1, 2, 3, 4,
5, 6, 7, 8, 9, 10 units or more.
The bevelled edge is divided into convenient equal divisions.
The circumferences of the circles are numbered 1 to 20, or higher or lower
enumeration.

page_text: The lever and consequently the moveable mirror are made capable of being
moved through a small arc after an observation has been taken either by means
of a tangent screw, a stop or suitable equivalent means capable of being regulated
according to requirement by a micrometer screw or otherwise.
The instrument is used as follows.
Any well defined object is chosen making a convenient angle (preferably not
less than 30°) with the direction of the object whose range is required, the angle
between these two directions is then recorded on the instrument by moving the
index mirror. The mirror and lever are then adjusted to an angle differing from
that angle by some small amount such for instance as from 45' to 2° 3.1 (forty five
minutes to two degrees thirty minutes) by the means mentioned above or such
adjustment may be made by means of another pair of mirrors giving the desired
angle.
The observer advances in the direction of the second object until this
increased angle is given by the mirrors. The base, i.e. the distance between the
first and this last point of observation is ascertained and the corresponding range
is read off the lever. Thus suppose the base is 75 yards the division on the lever
cut by the circle 7 is read and multiplied by 10 then that cut by the circle 5 and
the two are added.
If there is a decimal fraction in the base it can be similarly included, or inter-
mediate circles may be drawn to give readings intermediate to those given by the
circles numbered 1 to 20 or other convenient euumeration.
If desirable a fixed base may be used, in which case it will be necessary to vary
the difference angle, the same readings will be used, provided the base be first
multiplied by the fraction which may be shewn on the micrometer screw.
Amongst the advantages attendant upon the employment of the foregoing
method and apparatus is the fact that the base increases with increase of the
length of the range obviating thereby increased liability to error that would
otherwise arise.
Fig. 2 is a similar view of the disc shewn separately.
a is a metal frame carrying two mirrors as in an ordinary sextant. The index
mirror is silvered, and is capable of rotation about a central axis cat right
angles to the plane of the instrument.
The other mirror 6', called the horizon glass, is fixed, and half of it is silvered
and half plain glass.
Carrying the index mirror b is an arm d which rotates in a plane parallel to
that of the instrument, and is provided with a vernier scale d¹ to read angles on
a graduated are a¹ contained in the frame a. This arm carries with it a smaller
arme attached directly to the index mirror 6 and moving with the index arm d
about the same axis e; it is capable moreover of rotating through a small arc,
relative to the index arm, taking with it the index mirror b.
ور
The amount of arc is regulated by two screws d d³ attached to the large or
index arm d, one on each side, against either of which the small arme can be set
at will, and which can both be moved so as to increase. or diminish as desired the
play of the small arm; d² is called the "zero" screw, and the "difference
screw, the frame a also carries a metallic disc presenting a plane surface either
on the upper or lower side as most convenient; if on the upper side the disc is
depressed sufficiently below the plane of the graduated arc to permit of room for
the other parts of the instrument. On this disc are engraved a convenient
number of circular arcs starting from a common point at which they touch one
another.
3
About this point an arm f' with graduated straight edge is free to revolve,
the prolongation of which passes through the point f'. A chord is thus formed

page_text: to all the circular arcs such that in any position it is divided by the arcs into
equal parts.
The graduated edge is divided into equal divisions of convenient length,
say to go, or of an inch.
By suitable means this straight edge or cord is made to revolve at twice the
rate of the index arm d, and concurrently with it; to do this I employ cog
wheels, friction wheels, or a compound circular motion in a ratio of 2 to 1, the
arrangement for the latter, which has the advantage of dispensing with wheels
being as follows:-
The index arm d on its under side has a straight slot (not shown on drawing)
in the direction of its length, and such that the prolongation passes through the
central point about which it rotates; in this slot works a pin which is fixed to
the revolving chord at the same distance from the pivot point of the chord as the
latter is from the pivot point of the index arm.
The ares on the disc are numbered consecutively outwards.
As an alternative the arcs and revolving chord may be omitted, in which case
the graduated arc of the sextant is graduated to show, in addition to angles,
multiples of a base corresponding to the angles. In this form the invention may
be adapted to the ordinary box sextant thus providing a pocket instrument for
measuring both angles and ranges.
For convenience in measuring the base, there may be attached to the
instrument a bobbin on which a graduated cord, wire, tape or ribbon of suitable
material is kept wound up to zero by means of a spring. At the end of the tape
is a ring to pass over a stick, picket or rifle; as the operator carries the instrument
to the other end of the base the tape unwinds and shows the length required.
The instrument is used as follows:-
1. To measure angles-proceed as with a sextant.
2. To measure ranges:-
e. g. required the range of object X from point A.
(a) Choose a well defined object B which with X subtends any angle at A,
most suitably between 50° and 100°.
(b) Measure this angle by the instrument using it as a sextant, taking care
that the small arm attached to the index mirror is pressed against the difference
screw.
(c) Shift the arm to the zero screw.
(d) Move with the instrument from A on the straight line A. B. towards B and
stop at the point at which the angle then subtended by B and X is recorded by
the instrument, this being equal to the original angle at A increased by the
"difference angle."
(e.) Measure the base so obtained and read off the range on the revolving
chord; or the number on the graduated arc indicated by the index arm and
multiply it by the base to give the range.
N.B. If more convenient the operation may be reversed, that is to say, the
larger angle measured first and the base measured in the opposite direction.
3. To adjust the screws:-
(f) Set the small arm against the zero screw d² and move the index arm d by
means of the tangent screw d (or otherwise) until the range indicated is zero; if
the mirrors are parallel (ascertained as in sextant) the zero screw is adjusted, if
not, turn the zero screw d² until after trial the mirrors are parallel.
(g.) Set the arm e against the difference screw d³ and adjust that until the
index arm d records the angle for which the instrument is graduated.
The zero screw d' is the screw on that side of the index arm d towards which
the arm moves to increase the angle indicated.
The difference angle is the difference between the angles at either end of the
base, its magnitude fixes the size of the circular arcs and therefore determines the
graduation of the instrument. For a difference of 1° 30' the diameter of the circular
are marked 10 is 38-202 times a single division on the revolving chord, or the

page_text: graduation opposite 90° on the graduated sectant arc is 38-202 or 38.2 approxi-
mately.
Each instrument shows the angle for which it is graduated, but any other angle
may be used not greater than 2°, the result as recorded being proportionately
increased or diminished according as the angle is smaller or larger than the
normal difference angle of the instrument.
Amongst the advantages attendant upon the use of the improved instrument are
The base may be taken in any most suitable direction and not necessarily in a
fixed direction relatively to the range nor restricted within a small number of
degrees.
Advantage may be taken of any well defined object that presents itself without
the necessity of sending out a man or planting a picket.
The base is proportional to the range and therefore errors are not increased for
long ranges.
Many ranges may be taken from one point with a base fixed as to direction.
A surveying instrument is combined with a range-finder and thus a survey may
be made in open county from one spot.
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 [
claim is :-
1. The construction arrangement and combination of parts substantially as
herein shown and described constituting improved apparatus for use in ascertaining
the distances of inaccessible or other objects.
2. The method of and means or apparatus for ascertaining the distances of
inaccessible or other objects substantially as and for the purpose set forth.
3. In a range finder, or distance calculator, the construction and arrangement of
plotting table, or surface, having tangential co-axial circular circumferences
capable of co-operating with a protracting arm substantially as set forth more
particularly with respect to Fig. 2.
Dated the 22nd der of November 1892
WM. BROOKES & SON,
55 & 56, Chancery Lane, London, Agents for the Applicant.