IMPROVEMENTS IN RANGE FINDERS
Year: 1881

page_text: LETTERS PATENT to Francis Charteris, commonly called Lord Elcho, of
23, St. James Place, London, for an Invention of "IMPROVEMENTS IN RANGE
FINDERS"
PROVISIONAL SPECIFICATION left by the said Francis Charteris at the
Office of the Commissioners of Patents on the 26th August 1881.
FRANCIS CHARTERIS, commonly called LORD ELCHO, of 23, St. James Place,
London. IMPROVEMENTS IN RANGE FINDERS."
"
This Invention relates to the means of ascertaining the approximate distance
of objects, and more particularly of troops in action, without necessitating
calculation and without loss of time.
It consists in placing between the field and eye lenses of the eye piece of a
telescope a transparent disc of glass on which are visible a number of lines arranged
as steps, with a figure on the top of each step, said steps being placed over a
horizontal base line at distances corresponding to the apparent height of men
(mounted or dismounted) at different ranges, preferably from 200 to 2000 yards
for infantry, and from 300 to 2800 yards for cavalry. The figures at the top
of each step indicate the distance, preferably in hundreds of yards, the steps
marked with the initial I being for infantry and the steps marked C for cavalry,
the two stairs being as much as possible arranged symmetrically. Instead of
using the same disc for all distances two discs may be used, one for short distances
and the other for long distances, or one for cavalry and one for infantry, and they
may be all adapted to the same telescope so that either one or the other may be
used at a time, or different discs may be used with different telescopes.
The absolute size and distance of the steps depends on the construction and
power of the telescope, and may be ascertained either by calculation or by
experiment.
The division may be photographed, engraved, or otherwise produced on the glass
or transparent disc. The lines may also be represented by cobweb or other fine
material mounted on a frame instead of a disc.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said Francis Charteris in the Great Seal Patent Office on the
25th February 1882.
FRANCIS CHARTERIS, commonly called LORD ELCHO, of 23, St. James' Place,
London. IMPROVEMENTS IN RANGE FINDERS."
"
This Invention relates to the means of ascertaining the approximate distance
of objects, and more particularly of troops in action, without necessitating
calculation and without loss of time.
It consists in placing between the field and eye lenses of the eye piece of a
telescope a transparent disc of glass on which are visible a number of lines arranged
as steps, with a figure on the top of each step, said steps being placed over a
horizontal base line at distances corresponding to the apparent height of men
(mounted or dismounted) at different ranges, preferably from 200 to 2000 yards
for infantry and from 300 to 2800 yards for cavalry. The figures at the top of
each step indicate the distance, preferably in hundreds of yards, the steps marked
with the initial I being for infantry and the steps marked C for cavalry, the two
stairs being as much as possible arranged symmetrically. Instead of using the
same disc for all distances two discs may be used, one for short distances and the
other for long distances, or one for cavalry and one for infantry, and they may be
all adapted to the same telescope, so that either one or the other may be used at a
time, or different discs may be used with different telescopes.
The absolute size and distance of the steps depends on the construction and
power of the telescope, and may be ascertained either by calculation or by
experiment.
The division may be photographed, engraved, or otherwise produced on the glass
or transparent disc. The lines may also be represented by cobweb or other tine
material mounted on a frame instead of a disc.
In the accompanying Drawing, Figure shows the eye piece of a telescope
provided with a disc D to which my Invention refers, while Figure 2 is a front
view of the disc D showing the divisions on a larger scale. As discs provided
with plain horizontal divisions have already been used in telescopes for range
finding, I need not describe where and in what manner the disc should be secured
to the tube. I do not claim the application of discs provided with horizontal
divisions for indicating the distances, but the stair shaped arrangement of the lines
and figures, and the combination of two symmetrically arranged systems of lines
on the same disc, one for indicating the apparent height of infantry, and the other
the apparent height of cavalry at various distances, the whole substantially as
described.
In witness whereof, I, the said Francis Charteris, have hereunto set my hand
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T
1003
Witness,
W. GREGORY,
Optician,
51, Strand,
London.
ELCHO. (L.S.)