IMPROVED METHOD AND MEANS FOR RANGE FINDING
Year: 1881

page_text: LETTERS PATENT to Thomas Bolton of Calcutta in the Province of Bengal
in the East Indies for an Invention of IMPROVED METHOD AND MEANS
FOR RANGE FINDING
PROVISIONAL SPECIFICATION left by the said Thomas Bolton at the
Office of the Commissioners of Patents on the 15th December 1881.
THOMAS BOLTON of Calcutta in the Province of Bengal, in the East Indies
"AN IMPROVED METHOD AND MEANS FOR RANGE FINDING"
My Invention is designed for the purpose of range finding by means of a
system requiring a prismatical shaped box in which are four reflectors two in the
upper part of the box set at an angle of 45 degrees to each other and furnishing
a right angle by reflection and two in the lower part reflecting an angle of
88.° 34' 4" which angle forms one of the elements in a right angled triangle in which
the perpendicular and base are in the proportion of one to forty. In some cases
I employ a telescope provided with subtense wires suitably arranged as a means
for measuring the base.
The principle upon which the system is based may thus be briefly described
regard being had to the Sheet of Drawings annexed hereto as illustrative of the
general nature of the Invention
O AB (Fig. 4) is a right angle laid off from the line joining the fixed point O
to the point A, by means of two staves and of the prismatic shaped box described
hereinafter. The ne A¹ B is produced towards C in the line of the staves
planted at A'B', and a position C is found on the said line by means of the
prismatic box above alluded to, at which the angle included by the lines A¹ C
and CO of the right angled triangle O A' C is such that the side A¹ C is to
the side AO in the proportion of 1 to 20 or of one to 40 as the case may require.
Now if O be a distant object its distance A' O can be read off or computed when
A' C is known, O A' being 20 or 40 times A¹ C. The distance AC may be
obtained by actual measurement with a tape twine or chain, or by pacing it, or by
the help of a telescope used in combination with a standard proportionate scale
attached to the staff at A' and adapted to the subtense wires in the telescope.
The telescope and scale are not necessary parts of the apparatus but are intended
only as a mode of measurement that may be useful under certain circumstances.
For ranges up to 5000 yards the angle OC A has been adopted equal to
88°. 34. 4 which makes the sides A¹ C to A¹ O as 1 to 40; this proportion has
been found to be very convenient for the purpose.

page_text: A (Fig. 1) is a telescope which has two wires placed vertically and parallel
within the focus of the eye piece and adjusted to subtend a certain unit whose
length is dependent on the angle of the mirrors in the box, and the angle subtended
by the distance between the wires, on a given scale, by which means the range is
read off.
G (Fig. 3) is a graduated arm to be attached to the staff A and supported by the
staff D. It is divided into inches, 15 of which are each subdivided into 20 parts,
15 others each into 10 parts, and the rest up to 50 inches into 5 parts, each inch
being proportional to and representing a range of 100 yards; one subdivision of
the first 15 inches or one twentieth of an inch will therefore denote a distance of
5 yards, the tenth of an inch ten yards, and the fifth of an inch 20 yards
F (Fig. 2) is a small auxiliary telescope which can be attached to the prismatic
shaped box, and used for observing very distant objects; it is so arranged as not
to interfere with the working of the instrument when not in use.
The whole of the above can be packed into a canvas bag for convenionce and
portability.
METHOD OF FINDING THE RANGE.
Supposing the distance of any object O (Fig. 4) from an observer at A' to be
required to be determined the following are the directions to be observed:-Set
up the staff A at A' and with the prismatic shaped box lay off the right angle
O A¹ B' by resting the box upon the staff A and presenting its open face to Ŏ:
then place the eye at the edge of the open face of the box, as shewn in Fig. 6, look
through the aperture on the opposite side and note any object in the distance, or
spot on the ground, by direct vision, that coincides with the reflected image of O,
seen in the upper mirror d, in line with which place the staff B some 10 or 20
yards from A. Should it be found on reverting to A that the staff B has not been
placed in the correct position the staff A should be moved a little to the right or left
by the adjustment provided in the top of the tripod, till the right angle is correctly
formed by the reflected image of O coinciding with the staff B seen by direct
vision, care being taken that the staves are set upper pendicularly by the plummets
attached.
The staves A and B being correctly placed proceed to lay off the base A' C in
the line B A C fix the pin attached to the twine on the reel in the ground under
the staff A and walk backwards in the same straight line with A' B' allowing the
twine to run from the reel as required and holding the prismatic box as before to

page_text: the eye, when the staves A and B as seen in a direct line through the aperture,
coincide with the image of O as seen by reflection in the mirror e, the point C is
reached and the range may be read off from the numerals attached to the twine,
in which the marks represent forty times the natural length.
To obtain the range approximately and more expeditiously, the staff B and
measuring twine inay be dispensed with, simply by noting with the aid of the
prismatic shaped box, any object, however distant that may be seen to coincide
with the reflected image of O. To do this it may be necessary to move a little to
the right or left of the position selected for the staff A, and to alter the locality of
the staff accordingly. The position C being found as before the distance CA' inay
be paced back to A which multiplied by 40 will give the range required.
In hazy weather or when the distances are great, and the object too indistinct
to be seen by reflection, the process of finding the range will be the same except
that the prismatic box will have to be reversed and instead of the staves being
looked at through the aperture, their reflected images must be made to coincide
with the distant object seen by direct vision.
Ranges may be found at night also when a light, camp-fire, or other object in
the distance is in view, in which case the staves A and B should be illuminated by
small lamps fixed to the staff heads or by means of phosphorous.
In using the scale and telescope (Figs. 1 and 3) as a means of ineasuring the
base, the scale should first be erected horizontally on the staff A, and set to point
to the distant object O.
The position Chaving been found the telescope is placed on a stand at that point
and turned towards the scale attached to the staff A situated at A. The necessary
adjustment of focus having been performed the observer bisects the zero of the
scale, which is coincident with the centre of staff A, with the centre wire of tho
telescope and notes the number of divisions on the scale included between the two
wires, the corresponding numerals of which having been marked with a due regard
to the system of triangulation employed and to the construction of the telescope
furnish at once the range in yards.
The accuracy with which the range is obtainable by this system depends chiefly
in the first instance in laying off the right angle OA B' exactly; great care
therefore is necessary when observing with the prismatic shaped box, that the
reflected image of the distant object O coincides exactly with the staff B at
station A especially when the object and staff are not in the same plane, in which
case the instrument will require tilting a little to make the observation. In finding
the position C care must be taken to insure the true coincidence of the reflected
image of O with the line A' B₁
The method to be adopted in finding the range with regard to a moving object
is as follows:-
Let S (Fig. 7) represent a ship entering a harbour in a direction shewn by the
line SE for instance; supposing it to be required to find her distance during
some part of her course from a point A on the shore the following directions must
be observed. At A' set up the staff A and place the staff B in such a position B¹
that a line perpendicular to the line A¹ B' will intersect the line SE in some
point E, lay off the right angle E' A' D with the prismatic shaped box on the
opposite side of A' B' to S, and place a staff at D, behind which an assistant must
be stationed; then let the observer move along in the direction A' C and in line
with A and B till he sights the reflection of S in the lower mirror e in coincidence
with the staves A and B scen by direct vision; let him now proceed towards A' still
keeping the image of S coincident with the staves A and B until a prearranged
signal from the assistant warns him to stop the instant that S cuts the line DA'
produced towards E: then is the distance from that point occupied by the observer
in the line C A' when he received the signal to A' one fortieth of the distance A¹E.
The arrangements for laying off the right angle should be made some time previous
to the arrival of the object.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Thomas Bolton in the Great Seal Patent Office on the Sth June 1882.
THOMAS BOLTON of Calcutta in the Province of Bengal in the East Indies
"IMPROVED METHOD AND MEANS FOR RANGE FINDING."
It is designed for the purpose of "range finding "by means of a system requiring
a prismatical shaped brass box in which are four silvered glass reflectors two in
the upper part of the box set at an angle of 45 degrees furnishing a right angle by
reflection and two in the lower part reflecting an angle of 58° 34′ 4″ which forms
one of the elements in a right angled triangle having the perpendicular and base
in the proportion of one to forty
It may thus be briefly described, regard being had to the diagrams annexed
O. A'. B. (Figure 4) is a right angle laid off by means of prismatic shaped box
described hereafter and the staves A and B, the line A' B is then produced_to.C
guided by the staves A and B and a position C found on it also by means of the
prismatic box above alluded to where an angle is formed included by the lines
A¹. C. and C. O. forming a right angled triangle O. A¹. O of which the side A C
is to A. O. in the proportion of 1 to 20 or to 40 as the case may require. Now if
O be a distant object, the distance A' O is known when A¹C is known C A' 20 or
40 times AC respectively while A'C may be obtained by actual measurement
with a tape twine chain by pacing it-
For ranges up to 5000 ya:ds, the angle O. C. A¹ has been adopted equal to
88° 34' 3" which makes the sides A' C to A' O as 1 to 40, and which angle has
been found to be the most convenient for the purpose-Figure 1) Is a prismatic
shaped brass box fitted with two systems of mirrors, those in the upper portion
marked d d are inclined to each other at an angle of 45° furnishing a right angle
by reflection, while those in the lower part of the box and marked e, e, are inclined
to an angle of 44°; 17. 2" and reflect an angle of 88° - 34'-3" Two apertures are
on either side of the box and between each pair of mirrors on the same side serve
for the direct vision of any object when looked at through the open end of the
instrument A (Figure 2) Is a telescopic staff fixed to a li.ht tripod stand and
supplied with a horizontal adjustment and a plummet to insure its perpendicularity
when set up, B (Figure 2) Is a telescopic staff with an iron spike for fixing it in
the ground, it is also supplied with a plummet to set it up perpendicular (Figure 3)
is a metal reel containing strong twine marked for every 10 yards of range and
can be further subdivided by approximation-
The whole of the above are packed into a canvas bag for convenience and
portability.
METHOD OF FINDING THE RANGE
Let the distance of any object O (Figure 4) from an observer at A¹ be required,
set up the staff A at A¹, and with the prismatic shaped box lay off the right angle
O. AB by resting the box upon the staff A and presenting the open face to O, then
place the eye at the edge of the open face of the box, as shown in (Figure 5) look
through the aj erture on the opposite side and note any object in the distance or
mark on the ground by direct vision that may coincide with the reflected image.
of O, seen in the upper mirror d in line with which place the staff B some 10 or
20 yards from A should it be found on reverting to A that staff B has not been
placed in the correct position the staff A should be moved a little to the right or
left by the adjustment provided on the top of the tripod till the right angle is
correctly formed by the reflected image of O. coinciding with the staff B seen by

page_text: direct vision, care being taken that the staffs are set up perpendicular by the .
plummets attached-
The staves A and B being correctly placed the observer proceeds to lay off the
base AC guided by these staves, he fixes the pin attached to the twine on the
reel in the ground under staff A and walks backwards in the same straight line
with A B allowing the twine to run from the reel as required and holding the
prismatic box as before to his eye, looks into the lower reflector e, until he gets to
a position C where the staffs A and B seen in a direct line through the aperture
coincide with the image of O as seen by reflections in the mirror e at which place
he reads off the range from the numerals attached to the twine-
In hazy weather when the distances are great and the object too indistinct to be
seen by reflectors, the process will be the same except that the prismatic box will
have to be reversed and instead of looking at the staves directly through the
aperture their reflected images should be made to coincide with the distant object
seen by direct vision. Ranges may be found at night also when a light camp fire or
other object in the distance is in view in which case the staves A and B should be
illuminated by small lamps fixed to the staff heads or by means of phosphorous-
The accuracy with which the range is obtainable by this system depends chiefly
in the first instance in laying off the right angle O. A'. B great care is therefore
necessary when observing with the prismatic shaped box, that the reflected imago
of the distant object O coincides exactly with the staff B at station A' especially
when the object and staff are not in the same plane, when the instrument will
require tilting a little, to make the observation and secondly in finding the.
position C, care must be taken to insure the true coincidence of the reflected
image of C with the line A¹ B.
To facilitate Military operations the apparatus above described is divided into
two portions D D and E E and used by two or more persons one at position A' and
the other at position C having a measuring tape between them showing the distance
so that the two observations can be taken at one time and the distance of the
object O is obtained in a shorter time and with more facility than that obtained
by the use of the double instrument -
Having thus described the nature of the said Invention and the manner in
which it is to be performed I would have it understood that I lay no general claim
to the use of mirrors for laying off either a right angle or the angle of 88° 34′ 3″
any other elemental angle that may be selected taken separately but what I
consider to be novel and original and therefore do claim as secured to me by the
Letters Patent hereinbefore in part recited, is:-
1 The method of finding a range or distance by the use of four mirrors so
arranged that their angles of reflection are those of the base of a right angled
triangle whose sides about the right angle are as one to ten, twenty, or forty, sixty,
eighty, or one hundred and twenty &c., substantially as described
2 The use to find a range or distance of the improved reflecting apparatus
capable of division into two parts D. D. E E as herein above described.
In witness whereof I the said Thomas Bolton have hereunto set my hand
and seal this Sixteenth day of May in the year of our Lord One thousand
eight hundred and eighty two
Witness,
J. REMFRY
THOMAS BOLTON (L.S.)