IMPROVEMENTS IN INSTRUMENTS FOR ASCERTAINING DISTANCES, CHIEFLY DESIGNED AS RANGE-FINDERS FOR MILITARY PURPOSES
Year: 1880

page_text: LETTERS PATENT to Henry Hensoldt, of Forston Street, in the County of
Middlesex, for an Invention of " IMPROVEMENTS IN INSTRUMENTS FOR
ASCERTAINING DISTANCES, CHIEFLY DESIGNED AS RANGE-FINDERS FOR
MILITARY PURPOSES."
PROVISIONAL SPECIFICATION left by the said Henry Hensoldt at the
Office of the Commissioners of Patents on the 12th June 1880.
"IMPROVE-
HENRY HENSOLDT, of Forston Street, in the County of Middlesex.
MENTS IN INSTRUMENTS FOR ASCERTAINING DISTANCES, CHIEFLY DESIGNED AS
RANGE-FINDERS FOR MILITARY PURPOSES."
My Invention relates to range finders or instruments for ascertaining the
distance between two points or positions, and consists in improvements whereby
I produce an instrument chiefly designed for finding the range of artillery or
musketry expeditiously and accurately without the necessity of any multiplication
or other calculation on the part of the operator, which instrument or apparatus is
greatly superior to instruments of the same class as heretofore constructed, by
reason of its simplicity of construction, and from the fact that no special practice
or instructions are required to enable the manipulation of the same to be readily
understood.
In the use of range finders as heretofore ordinarily constructed, it has been
necessary to set out a triangle with a certain predetermined angle at the base, the
apex of the said triangle being the object whose distance from the operator or
operators is to be ascertained; or the base of the triangle in some cases extends in
a line with the object whose distance is to be ascertained. This method however
necessitates a series of separate operations; as, for instance, the laying off of an
imaginary base, the measuring of the length of such base, the determination of the
second angle at the base, and the after multiplication and other calculation to
attain the result desired. Several persons are generally required to take the
measurements and for other purposes. Moreover, it frequently happens that the
object whose distance to be ascertained is a movable one, such, for instance, as a
Prins 11

page_text: man on foot or mounted, in which case it frequently happens that before the
operations necessary for calculating the distance are completed he has disappeared
from view or has moved to another position, thereby rendering the whole attempt
futile.
My Invention is designed to obviate these difficulties and disadvantages, and to
produce an instrument which in a few seconds will afford an indication of the
exact distance of any object from the said instrument, and which can be manipulated
by one person, and may be readily transported or carried by such person, while
obviating the necessity for employing tapes or lines for measuring a base on which
to set out a triangle or other figure.
My said Invention is based upon the principle of indicating on a scale within a
telescope the height of the object whose distance is to be found, and then by the
comparison of the same with the actual height (known or estimated) of the said
object, to ascertain the distance of the same from the instrument.
One method of carrying the said Invention into practice is as follows, that is to
say I employ a telescope of the ordinary or other suitable construction, and
insert within the eye piece of the same a glass disc, which is provided with a
series of irregular or unequal divisions, that is to say, with lines not equi-distant
from each other, and which if desired may be suitably numbered. This glass disc
is preferably secured in a detachable tube, which may be readily inserted in or
The irregular
withdrawn from the eye piece of the telescope when desired.
gradations or divisions on this glass disc must be adapted to the height of some
well known object. One very convenient height is that of a man, which averages
about five feet eight inches, and as there are many other objects in nature which
are of the same or approximately the same height, I have found that a disc
provided with divisions to suit this height may be very advantageously employed
for military purposes.
In order to ascertain the distance of any object, say a man, the operator having
brought him in view, first ascertains by the length of the image projected on the
disc whether he is within 200 yards. If so the telescope is adjusted so that the
feet of the man touch the lower horizontal division or line on the glass disc. The
operator then observes which line or division of the disc coincides with the top of
the man's head, and then takes the number marked at the sido of the scale on the
said division or counts the number of divisions from the upper one; he is thereby
enabled to estimate the distance, as the space between each division represents a
certain number of yards.
When the distance of the object is found to be beyond 200 yards the highest
point of the same is brought in line with a central horizontal line on the aforesaid
disc, and the number of divisions between the lowest point of the object and the
lower line or division on the disc then give the distance of the object.
From the above description it will be readily understood that the only operations
required are, first, to bring the object into focus, then adjust the telescope to bring
the bottom division (if within 200 yards, or the central division if beyond that
distance) on the glass disc into line with the lower or upper point of the object,
and then to observe the number of the line or to count the number of divisions
whereby the distance is readily estimated. When the distance of objects of greater
height than a man is to be ascertained, the disc in the telescope must be replaced by
another disc graduated to suit the estimated height of the object, whose distance
may then be readily ascertained in the manner above described.
To render the said instrument especially applicable for ascertaining long distances
for ordnance firing I modify my improvements as follows, that is to say :-Instead
of employing a glass disc provided with divisions at varying distances from each
other, as above described, I arrange in the interior of the telescope, and at one side
of the same a glass plate provided with numbered divisions or gradations. On a
level with the lower division I stretch horizontally across the telescope a filament
or thread of cobweb or other fine line, which is immovably secured and serves as a
base line, that is to say, as a line whereon the base of the object whose distance is

page_text: to be ascertained is made to coincide. Above this fixed line I arrange another
cobweb or line, which is attached to a plate capable of sliding vertically, and
adjustable by a milled headed screw or other suitable device. The plate carrying
the said cobweb or line is provided at its upper part with lugs, which fit over and
are free to slide vertically upon two rods, preferably surrounded by spiral springs
to constantly press the said plate upward. The lower portion of the plate is
provided with an extension having a screw threaded hole with which the end of
the screw engages. Below the telescope and formed on or attached to the shank
of the said screw is a disc having numbered divisions upon its periphery, and over
the edge of this disc extends a finger or pointer fixed to the box containing the
aforesaid threads and the sliding plate. The divisions on this disc indicate fractions
of those on the aforesaid glass plate. When it is desired to ascertain the distance
of an object with this instrument the fixed or base line of the instrument is made
to coincide with the base of the distant object whose image is projected on the glass
plate; then by turning the aforesaid screw the movable line is adjusted to coincide
with the top of the said object. By thus turning the screw the disc provided with
divisions on its periphery is also turned behind the fixed pointer. The operator
then takes the number of the division on the glass plate opposite to the movable
thread and the number of the division opposite the fixed pointer. The said
graduated disc affords means for ascertaining the exact position of the said movable
line when the same is between any two of the divisions on the glass plate. Then
by the aid of a chart or table with vertical and horizontal columns of figures to suit
the instrument, the operator is enabled at once to ascertain the distance or range of
the object from the instrument.
By the employment of the movable thread in combination with a fixed thread, as
above described, I avoid the necessity of a series of divided discs for objects of
different heights, as by estimating the height of the object whose distance is to be
ascertained, and employing a chart or table calculated to suit such height I am
enabled with the one instrument to find the distance of any object, whatever the
height of the same may be.
My improved range finder is preferably provided with means for supporting it on
a stand, and with suitable adjusting devices. For the longitudinal adjustment of
the eye piece of the telescope I prefer to provide the same with a longitudinal
rack gearing with a pinion turned by a thumb nut on the second section of the
telescope.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Henry Hensoldt in the Great Seal Patent Office on the 11th
December 1880.
HENRY HENSOLDT, of Forston Street, in the County of Middlesex.
"IMPROVE-
MENTS IN INSTRUMENTS FOR ASCERTAINING DISTANCES, CHIEFLY DESIGNED AS
RANGE-FINDERS FOR MILITARY PURPOSES."
My Invention relates to instruments for ascertaining the distance between two
points or positions, and consists in improvements whereby such instruments are
made to serve very advantageously as range-finders, that is to say, for finding the
range of artillery or musketry expeditiously and accurately, and I am thereby
enabled to produce an instrument or apparatus greatly superior to those heretofore
constructed for like purposes, by reason of its simplicity and its capability of being
used without multiplication or other calculation, or any special practice or scientific
knowledge or training on the part of the operator.
In the use of range-finders, as heretofore ordinarily constructed, it has been in
most cases necessary to set out a more or less extensive base line, the measurement
of which and the determination of certain angles necessitate a more or less
complicated calculation, and in some instances a considerable degree of physical
exertion on the part of the operator, and very frequently the co-operation of several
persons.
My Invention is designed to obviate the above difficulties and to produce an
instrument which in a few seconds will afford an indication of the exact or nearly
exact distance of any object from the said instrument, which can be manipulated by
one person, and may be readily transported or carried by such person, while
obviating the necessity of employing tapes or lines for measuring a base whereon
to set out a triangle or other figure.
My said Invention is based upon the principle of indicating the height or any
other dimension of the object whose distance is to be found on a scale within a
telescope, and then by comparison of this indicated dimension with the actual
height or dimension (known or estimated) of the said object, ascertaining the
distance of the latter from the instrument.
In order to accomplish this result, the exact magnifying power of the telescope
which is to be used must be known; this can be ascertained by measuring the
focal length of the two front lenses (the objective) of the telescope, and by taking
into consideration the magnifying power of the eye-piece. Knowing the height or
the approximate height or other dimension of an object, I am able to calculate the
apparent size thereof within the focus of the instrument, at any given distance
from the latter, between a minimum and a maximum distance. And after having
ascertained the magnifying power of the telescope, and having theoretically
ascertained the variations in the apparent size of the said object at various distances,
I construct a scale, indicating those variations by fine but distinct lines on a glass
disc. This glass disc is preferably secured in a detachable tube, which may be
readily inserted in or withdrawn from the eye-piece of the telescope when desired.
The irregular graduations or divisions on this glass disc must be, as above specified,
adapted to the height or other dimension of some well known object. One very
convenient standard of measurement is the height of a man, which averages about
five feet eight inches; and as there are many other objects in nature which are of
the same or approximately the same height or length, I have found that a disc
provided with divisions to suit this height may be very advantageously employed
for military purposes. It is well understood that the shorter the distance or range
of the object from the instrument the longer will be the image thereof on the disc,

page_text: Figure 5 a side elevation, and
Figure 6 a central longitudinal section of a portion of a modified form of range-
finder constructed according to this Invention.
Figure 7 is an end view looking towards the rear end of the range-finder, portions
of the instrument being removed to indicate more distinctly the details of
construction of the same.
Figure 8 represents on an enlarged scale the measuring lines used in the said
modified form of range finder.
Figure 9 is an elevation drawn to a reduced scale, and
Figure 10 a transverse section on the line x, x, Figure 9, illustrating a method of
adjusting the eye-piece of the telescope.
Like letters indicate the same parts throughout the Drawing.
I will first more particularly describe the instrument shewn in Figures 1, 2,
and 3, in which a represents a telescope of the ordinary construction within which
I insert the eye-piece b; the latter is provided with a glass disc c having a series
of irregular or unequal divisions, that is to say, the said disc has upon it a series
of lines or divisions unequally distant from each other, as shewn in Figure 3, which
lines if desired may be suitably numbered, as shewn. This glass disc c is preferably
secured in a detachable tube d, which may be readily inserted in or withdrawn
from the eye-piece bof the telescope when desired.
My scale is divided by a central line into two parts, which for convenience I
will term the upper and the lower part. In the upper part or half the graduations
are separated by wider intervals than in the lower half, and during the determi-
nation of a distance the eye-piece of the telescope which contains the scale must
be turned to bring the lines of the scale into a horizontal position if the vertical
dimension of the object is to be taken, or in any other required position, according
to the dimension which is to be observed. In the disc shewn in Figure 3 the upper
half of the scale has ten divisions, each denoting a difference of 10 yards in the
range or distance of the object; for instance, if the latter should reach from the
lowest line c' of the scale to the fifth division in the upper half of the scale, the
distance of the object would be 150 yards, taking 100 yards as the minimum
distance to be ascertained. For all distances between 100 yards and 200 yards the
lowest line c¹ of the scalo will serve as a base line, that is to say, the line which
will coincide with the lowest point of the dimension determined upon; and as each
division of the upper half indicates a difference of 10 yards it will be understood
that when the image of the object extends from the lowest line of the whole scale
only to the central line c³ its distance is 200 yards. If the range or distance is
greater than 200 yards, the image will be found to fill less than one half of the
scale, and then the lowest line of the scale must no longer be used as a base for the
image's lowest point, that is, as a base for the lowest point of the dimension
determined upon, but the image's highest point must be brought level with the
central line of the scale, and the divisions must be counted from the lowest line of
the scale to the image's lowest point.
As far as 400 yards I have found it practicable to use divisions, each representing
10 yards; from 400 to 500 the divisions are so arranged as to each represent 20
yards, and from 500 to 2,000 yards each division represents 100 yards.
And as
the intervals between the division-lines can easily be mentally subdivided into 10

page_text: parts, the distance of the object can be ascertained with a degree of accuracy more
than sufficient for military purposes.
In using this instrument the operator having the man or other object in view
first observes whether the image projected on the disc extends over more than one
half of the scale; if so, the telescope is adjusted so that the feet of the man touch the
lowest horizontal division or line c¹ on the glass disc. The operator then observes
which line or division of the disc coincides with the top of the man's head, and
then takes the number marked at the side of the scale on the said division, or
counts the number of divisions from the upper one; he thereby at once ascertains
the range or distance. When the distance of the object is so great that the image
of the latter extends over less than one half of the scale, the highest point of the
object is brought in line with the central horizontal line c² on the aforesaid disc,
and the number of divisions between the lowest point of the object and the lowest
line on the disc will then shew the range or distance of the object.
From the above description it will be readily understood that the only operations
required in using my improved instrument are, first, the focussing of the object,
then adjusting the telescope to bring the bottom division or the central division on
the glass disc into line with the lower or upper point of the object, and then
observing the number of the line which coincides with the other extreme point, or
counting the number of divisions as aforesaid.
When the object whose distance is to be ascertained is of dimensions that cannot
be conveniently estimated by comparison with the height of a man, the aforesaid
disc in the telescope must be replaced by another disc graduated to suit the
estimated height or other dimension of such object, whose distance may then be
readily ascertained in the manner above described.
It would have been casy to have used a scale in which the lowest line would serve
as a base for all objects without exception, but as the clearness or distinctness of
an object presented in a telescope is in proportion to its proximity to the centre of
the field of view, and as it is of essential importance that especially the more distant
objects should be very clearly seen in order to obtain correct results, the scale has
been arranged in the manner above described, and by this arrangement the greatest
distances are indicated on the portions of the said scale nearest to the centre of the
field of view.
I modify my improvements as follows, that is to say-Instead of employing a
glass disc provided with divisions at varying distances from each other, as above
described, I arrange in the eye-piece of the telescope, and so as to obscure a small
portion of the field of view of the latter, a small piece of metal or other material
provided on its inner edge with teeth e, whose points are equidistant from each
other. Or I may use a glass plate with equal divisions or graduations. This
contrivance is situated somewhat at one side of the interior of the eye-piece of the
telescope, and its highest point, or what is more essential the point of the highest
of the teeth (or the highest line of the graduations) is placed in line with the
central point of the field of view, and the series of teeth (or graduations) extends
therefrom to the lower part of the field of view. Across the latter, and level with
the upper graduation or highest of the teeth, I stretch a filament or thread f of
cobweb, which is immovably secured in its place; or I insert a glass disc with an
engraved line. Across the upper part of the field of view I fix another line f',
parallel to the line f. These lines f, f¹, serve two purposes, viz., Istly, as base-lines,
or lines on which one extremity of the object must be brought before its distance
can be found; and 2ndly, as boundary lines, or indicators of the maximum and
minimum distances which can be ascertained by the said instrument.
In com-
bination with these two fixed lines f, f', I arrange another cobweb or line ƒ³,
which is attached to a plate g, capable of sliding vertically while keeping this line
parallel with the fixed lines; the said plate is adjusted by a screw j or other suitable
device. The plate carrying the line is provided at its upper part with lugs or
guiding blocks gl which fit over and are free to slide upon two rods h, one of which

page_text: is preferably surrounded by a spiral spring i arranged to constantly press the said
plate upward. The lower portion of the plate g is provided with an extension g³,
having in it a screw-threaded hole, with which the end of the screw j engages.
Below the telescope, and formed on or attached to the shank of the said screw, is a
disc or vernier k, having numbered divisions on its periphery; and over the edge of
this disc extends a finger or pointer Z fixed to the box which contains the aforesaid
lines and sliding plate. The divisions on this disc indicate fractions of those of
the aforesaid teeth or scale.
The space between the two fixed lines represents a pre-determined distance,
which differs only in accordance with the height of the object, while the space
between the upper fixed line and the lowest of the teeth or graduations e indicates
the minimum distance that can be ascertained. This minimum distance also varies
according to the height or other dimension of the object whose distance is to be
ascertained.
When it is desired to find the range or distance of an object with this instrument,
it is necessary first to ascertain within what scope this distance may fall, that is to
say, into what portion of the telescopic field of view the image of the object is to
be brought. In every case the height or other dimension of the object must be
approximately known, as on the correctness of this knowledge depends the accuracy
of the result. When it is found that the object is within au observable distance,
that is to say, when its image presented in the instrument is not longer than the
entire scale, one of its extremities must be brought level with the upper fixed
line fi; then if the other extremity projects beyond the line f, the movable line f
must be moved to touch this extremity by turning the nut ke. The operator then
counts the number of the teeth or divisions from the central line f; and if the
movable line f' is not exactly level with one of the points of the teeth, he must
not only count the number of teeth from the central line f, but must also read off
the excess on the vernier k. The intervals between the teeth or divisions, as
aforesaid, are equal, and each represents one revolution of the screw; the vernier
being divided into 100 parts gives by means of the index or pointer a very
correct indication of the fraction.
If the image of the object should be so small in the telescope as to necessitate
the elevation of the movable line fabove the centre line f, the distance of the
object is beyond the limit represented by the half scale or space between fand f¹.
In this case the object's highest point must no longer be brought in line with the
upper fixed line f¹, but must be made level with the centre line f. In each case
the number of teeth from the centre downward with the excess read off on the
vernier allows the distance of the object to be ascertained as follows:-After these
figures have been obtained the operator refers to a table or chart with vertical
and horizontal columns of figures especially calculated for this purpose, and within
a few seconds, without any calculation, he can read off the distance. The tables
are so arranged as to present columns containing the number of teeth or of
revolutions of the vernier and their successive fractions with the corresponding
number of yards opposite. Thus if the number of teeth be three, and the fraction 45,
the distance will be found opposite the figures 3,45 of the index column. Each
table is so constructed as to consist of two parts; one part gives the distances of
the nearer objects, viz., those of which one extremity must be brought on the
upper fixed line f¹, while the other part must be referred to in cases where one
extremity of the object has to be level with the central line f.
By the modification of my Invention wherein I employ the movable line in
combination with two fixed lines, as above described, I avoid the necessity for a
series of discs for objects of different heights or dimensions, as by estimating the
height or other dimension of the object whose distance is to be ascertained, and
employing a table calculated to suit such height or dimension, I am enabled with
the one instrument, and without changing the scale therein, to find the distance of
almost any object, whatever the height or other dimension of the same may be.

page_text: My improved range-finder is preferably provided with means for supporting it
on a stand and with a suitable adjusting apparatus.
To facilitate the vertical adjustment of the telescope I provide the same with
the following devices, that is to say :-I secure to the telescope by means of a clamp
or clamping ring m and screw m', a pivot or plug which is adapted to revolve
within a T-piece m² whose lower arm is so constructed as to fit an aperture or
socket in the stand for supporting the telescope. Upon the said pivot I arrange a
clamping ring n provided with a clamping screw n', which when loosened allows
the ready adjustment of the telescope in a vertical direction. Projecting from this
clamping ring n is the arm n2, which when the required adjustment of the
telescope has been approximately effected and the ring n has been clamped by
the screw n¹, permits a further and very minute or accurate adjustment as follows,
that is to say-At one side of the arm n I arrange a spring n³, which tends to
constantly force the said arm in one direction. On the other side is a screw n*,
which on being turned moves the arm n³ in the contrary direction, thus enabling
the telescope to be minutely and completely adjusted to the exact position required
after the quick approximate adjustment thereof, as above described.
For the longitudinal adjustment of the eye-piece of the telescope, I in some
cases provide the same with a longitudinal rack b' gearing with a pinion at 6³,
turned by a thumb-nut 63 on the second section of the telescopo a.
In the arrangement illustrated in Figures 9 and 10 for adjusting the eye-piece b,
I arrange upon the said eye-piece a clamp o provided with a clamping screw o¹,
and upon the second section of the telescope I provide a lug p¹ to which a screw 2
is secured. This screw passes through a tapped hole in the aforesaid clamp o.
When the screw o¹ is loosened it permits the eye-piece to be moved in or out
approximately to the extent desired without affecting the position of the said
clamp. To then effect an accurate adjustment of the said eye-piece the screw o' is
tightened, and thereby compresses the clamp o tightly upon the eye-piece b, I then
turn the screw p. By this means a very minute longitudinal adjustment of the
eye-piece may be effected to ensure the proper projection of the object whose
distance is to be ascertained within the telescope.
Having thus fully described my said Invention and shewn how the same may
be conveniently and advantageously carried into practice, I wish it understood
that I claim,
First. The combination with a telescope of a glass disc marked with a scale,
the spaces or divisions of which are unequal, and which is graduated according to
the magnifying power of the instrument, and inversely in proportion to the
distance to be indicated thereby, in such a manner that the greater the range or
distance of the object the more central will be its indication on the disc by the
lines thereon for the purposes specified.
Second. The modification of my Invention wherein I employ the scale or series
of equidistant teeth or divisions with two fixed lines and one movable line
arranged in combination therewith, as and for the purpose specified.
Third. The improved devices consisting of the sliding plate to which the
movable thread or line is attached, and the screw in combination with the
graduated disc or vernier and pointer arranged, and operating substantially as set
forth and for the purpose specified.
In witness whereof, I, the said Henry Hensoldt, have hereunto set my hand
and seal, this Tenth day of December, in the year of our Lord One
thousand eight hundred and eighty.
HENRY HENSOLDT. (L.S.)