IMPROVED MEANS AND APPARATUS FOR MEASURING DISTANCES, APPLICABLE FOR RANGE FINDING AND OTHER MILITARY AND SURVEYING OBSERVATIONS
Year: 1879

page_text: LETTERS PATENT to Ebenezer Erskine Scott, of No. 14, Marlborough Road,
Lee, in the County of Kent, for the Invention of "IMPROVED MEANS AND
APPARATUS FOR MEASURING DISTANCES, APPLICABLE FOR RANGE FINDING AND
OTHER MILITARY AND SURVEYING OBSERVATIONS."
Sealed the 12th September 1879, and dated the 18th March 1879.
PROVISIONAL SPECIFICATION left by the said Ebenezer Erskine Scott at
the Office of the Commissioners of Patents on the 18th March 1879.
<<
EBENEZER ERSKINE SCOTT, of No. 14, Marlborough Road, Lee, in the County of
Kent. IMPROVED MEANS AND APPARATUS FOR MEASURING DISTANCES, APPLICABLE
FOR RANGE FINDING AND OTHER MILITARY AND SURVEYING OBSERVATIONS."
My Invention relates to means and apparatus for ascertaining the distances of
objects which are themselves inaccessible to the observer, as in finding ranges for
musketry or artillery, or for military or civil surveying. The operation which I
adopt for this purpose is to determine by actual measurement the base of a right
angled triangle, which has at its vertex the distant object and a known vertical
angle, and I select the vertical angle such that its tangent or sine is a definite
fraction, as, for example, one hundredth of the radius. Calling, the reciprocal of
this fraction the coefficient of the instrument I have only to multiply the measured
base by this coefficient in order to ascertain the distance of the object measured
along the perpendicular side of the triangle when I use the tangent, or along the
bypotenuse when I use the sine of the angle for the computation. For the
purpose of determining a triangle such as I have described, I employ an instru-
ment constructed on the principle of the sextant, but having the movement of its
radius limited by definite stops so that it is capable of observing only two angles,
one of them a right angle and the other an angle greater than a right angle by the
intended vertical angle of the triangle. The construction of the instrument is as
follows: On a rigid base plate I mount a radius working on a vertical pivot, and
carrying a mirror, the upper half of which is unsilvered. At the side of the radius
and near its mirror I fix on the base plate another mirror, so set that when the
radius is against a stop on the base plate at one extreme of its stroke, the two
mirrors are inclined to one another at an angle of 45°; and I fix on the base plate
.

page_text: another stop against which the radius can be pressed, the angle through which it
with its mirrors is turned from the one stop to the other being half the desired
vertical angle of the triangle. When an observer looks through an eye piece at
the end of the base plate at the radius mirror and sees through its transparent part
one distant object, and in its silvered part the image of another object coinciding
with the former, he knows that the lines of sight to those two objects form an
angle with one another, which in the one position of the radius is a right angle and
in the other position of the radius exceeds a right angle by double the angle
through which the radius is moved from the one stop to the other. The instrument
is with advantage enclosed in a case of wood or other light material, with lateral
sight holes provided with suitable covers. The mirrors and also the stops for the
radius may be made adjustible, so that the instrument can be at any time set by
applying it to the measurement of known distances before using it for ascertaining
distances that are unknown. Having got the instrument accurately adjusted I
apply it to measure the distance of an inaccessible object in the following manner :-
Setting the radius against the one stop I find a position in the field such that I see
in the radius mirror, the coincidence of the distant object with a pole set up at
some distance to right or left, and I mark this position by a pole. The line of the
two poles gives the direction of the base of the triangle. I then having set the
radius against the other stop move to a point in the line of the base, where the
distant object as viewed through the instrument coincides with the image of the
first pole, the distance of this point from the first pole being measured as the length
of this base of the triangle. I multiply this length by the coefficient to which the
instrument is set, and thus obtain the distance of the observed object. The instru-
ment may be simplified by using it in an inverted manner as follows:-Instead of
providing a radius moveable between definite stops I fix the two mirrors so that
they suit the observation of an angle a little less than a right angle, and then by
inverting the instrument I can observe another angle which is as much greater than
a right angle. The difference of the two angles thus observed forms the vertical of
an angle of an isosceles triangle, which when the angle is very small may be taken
to have its base in the same proportion to its side as the said angle or its chord
bears to the radius. Having thus fixed the small angle to which the instrument is
permanently set, which angle I preferably choose, such that its chord is a definite
fraction, such as one hundredth of the radius, I proceed with the operation, as
already explained, measuring the base and multiplying by the coefficient of the
instrument in order to ascertain the length of the side of the triangle which is the
distance required.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Ebenezer Erskine Scott in the Great Seal Patent Office on the 17th
September 1879.
EBENEZER ERSKINE SCOTT, of No. 14, Marlborough Road, Lee, in the County of
Kent. IMPROVED MEANS AND APPARATUS FOR MEASURING DISTANCES, APPLICABLE
FOR RANGE FINDING AND OTHER MILITARY AND SURVEYING OBSERVATIONS."
My Invention relates to means and apparatus for ascertaining the distances of
objects which are themselves inaccessible to the observer, as in finding ranges for
musketry or artillery, or for military or civil surveying. The operation which I
adopt for this purpose is to determine by actual measurement the base of a right
angled triangle, which has at its vertex the distant object and a known vertical
angle, and I select the vertical angle such that its tangent or sine is a definite
fraction, as, for example, one hundredth of the radius. Calling the reciprocal of
this fraction the coefficient of the instrument I have only to multiply the measured
base by this coefficient in order to ascertain the distance of the object measured
along the perpendicular side of the triangle when I use the tangent, or along the
hypotenuse when I use the sine of the angle for the computation. For the purpose
of determining a triangle such as I have described, I employ an instrument con-
structed on the principle of the sextant, but having the movement of its radius
limited by definite stops so that it is capable of observing only two angles, one of
them a right angle and the other an angle greater than a right angle by the intended
vertical angle of the triangle. The construction of the instrument is as follows:-
On a rigid base plate I mount a radius working on a vertical pivot, and carrying
a mirror, the upper half of which is unsilvered." At the side of the radius and near
its mirror I fix on the base plate another mirror, so set that when the radius is against
a stop on the base plate at one extreme of its stroke, the two mirrors are inclined
to one another at an angle of 45°; and I fix on the base plate another stop against
which the radius can be pressed, the angle through which it with its mirror is
turned from the one stop to the other, being half the desired vertical angle of the
triangle. When an observer looks through an eye piece at the end of the base
plate at the radius mirror and sees through its transparent part one distant object,
and in its silvered part the image of another object coinciding with the former, he
knows that the lines of sight to those two objects form an angle with one another,
which in the one position of the radius is a right angle, and in the other position of
the radius exceeds a right angle by double the angle through which the radius is.
moved from the one stop to the other. The instrument is with advantage enclosed
in a case of wood or other light material, with lateral sight holes provided with
suitable covers. The mirrors and also the stops for the radius may be made adjustable,
so that the instrument can be at any time set by applying it to the measure-
ment of known distances before using it for ascertaining distances that are
unknown. Having got the instrument accurately adjusted I apply it to measure
the distance of an inaccessible object in the following manner :-Setting the radius.
against the one stop I find a position in the field such that I see in the radius
mirror the coincidence of the distant object with a pole set up at some distance to
right or left, and I mark this position by a pole. The line of the two poles gives
the direction of the base of the triangle. I then, having set the radius against the
other stop, move to a point in the line of the base where the distant object as
viewed through the instrument coincides with the image of the first pole. The
distance of this point from the first pole being measured as the length of the base
of the triangle I multiply this length by the coefficient to which the instrument is
set, and thus obtain the distance of the observed object. The instrument may be
simplified by using it in an inverted manner as follows:-Instead of providing a
radius moveable. between definite stops I fix the two. mirrors so that they suit the.

page_text: observation of an angle a little less than a right angle, and then by inverting the
instrument I can observe another angle, which is as much greater than a right
angle. The difference of the two angles thus observed forms the vertical angle of
an isosceles triangle, which when the angle is very small may be taken to have its
base in the same proportion to its side as the said angle or its chord bears to the
radius. Having thus fixed the small angle to which the instrument is permanently
set, which angle I preferably choose, such that its chord is a definite fraction, such
as one hundredth of the radius, I proceed with the operation, as already explained,
measuring the base and multiplying by the coefficient of the instrument in order
to ascertain the length of the side of the triangle, which is the distance required.
DESCRIPTION OF THE DRAWING.
Fig. 1 represents a plan of one form of instrument, according to my Invention,
for operating as above described. It consists of a casing A within which is mounted
(on the base of the casing) a radius B, capable of being turned a little on a pivot.
On the radius is fixed a mirror C, the upper part of which is unsilvered as in a
sextant mirror, and in the casing at the side of the radius is fixed another mirror D.
Sight holes E, F, and G are provided through the ends and one side of the casing,
and these holes are by preference furnished with suitable caps or covers, so as to
prevent access of dust or dirt when the instrument is not in use. The eye hole E
may also be fitted with a telescope, and the mirrors may be of the prism kind. The
rdius B is capable of movement only between two fixed stops H, K, and the
amount of its movement may be adjusted by setting screws L. There may be a
small circular are graduated on the base of the casing, and at the end of the radius
with a vernier scale if desired to measure the angle through which the radius is
moved, but such graduation is not necessary for use of the instrument, as I will
presently describe. The radius B may be moved between the stops by hand applied
to it directly, but it is of advantage to move it by mechanism of the following
description: An eccentric M is mounted on an axis on the base of the casing, so
that it can be turned within certain limits by the finger applied to the axis thereof.
It works between two springs N, N, affixed to the radius, so that by turning the
eccentric M partly round in the one direction or the other the radius is caused to
move up to the one or the other of the two stops H or K. I operate with this
instrument in the following manner:-I will suppose that when the radius is
against the one stop H the mirrors C and D are at an angle of 45° to one another,
then on applying the eye at E and looking through the mirror C to a distant object
I will see in the same mirror the reflected image of an object, from which rays pass
as indicated by the dotted lines G, D, C, E, the line G, D, being at right angles to
C, E. If now I move the radius against the other stop K the inclination of G, D,
to C, E, will be altered by double the angle through which the radius has been
moved. I apply this mode of observation to ascertain the distance of an object, as
will be understood by reference to the diagram Fig. 2, in which O represents the
distant object; P, a station at which the line of sight O, P, thereto and another
line of sight P, R, are at right angles; and Q, a station at which the lines O, Q,
and Q, R, are at an angle to one another differing from a right angle by the vertical
angle O, which is double that through which the radius of the instrument has been
moved from the one stop to the other. This angle may conveniently be taken,
such that P, Q, the tangent of O to radius O, P, is a definite fraction such as 100th
of the radius. Having therefore measured the base P, Q, I have only to multiply
it by the reciprocal of the known fraction, or the coefficient of the instrument, which
in the case assumed would be 100 to ascertain the distance P, O. Otherwise, the
line Q, P, may be taken as the sine of the angle O to radius Q, O, which distance
may be similarly determined. As a modification of the instrument I so adjust the
stops for the radius as to determine the base of an isosceles triangle, as indicated
diagrammatically at Fig. 3, the angle S when the radius is against the one stop
being a little less than a right angle, and the exterior angle T when the radius is

page_text: against the other stop being as much greater than a right angle. This mode of
operating is of advantage, as by inverting the instrument the exterior and interior
angles may be taken on either side of the triangle, and the one observation can be
used to check the other and to facilitate the adjustment of the instrument. The
radius instead of being moveable may be fixed so as to give a definite angle S, and
it will then when the instrument is inverted give the same angle at T. Obviously,
instead of employing one instrument first at one station and then at another two
instruments equally adjusted may be used simultaneously by two observers at the
opposite end of the base of the triangle; this method of operating being useful
when the distant object O is in motion, as, for instance, a ship approaching to or
receding from a port.
Having thus described the nature of my Invention, and in what manner the same
is to be performed I claim,--
Measuring the distance of an object by ascertaining the length of base subtending
a known vertical angle at the object by means of an instrument, so constructed that
by mirrors adjustable within definite limits the reflected images of points at the
extremities of the base are respectively brought into coincidence with the object
observed, the distance thereof being thereupon computed by multiplying the
measured base by the known constant coefficient to which the instrument is
adjusted, substantially as herein described.
In witness whereof, I, the said Ebenezer Erskine Scott, have hereunto set my
hand and seal, this Sixteenth day of September, in the year of our Lord
One thousand eight hundred and seventy nine.