AN IMPROVED RANGE FINDER OR INSTRUMENT FOR MEASURING AND ASCERTAINING DISTANCES
Year: 1883

page_text: LETTERS PATENT to Francis Weldon of Hale Crescent; Farnham, in the
County of Surrey, Colonel in the Madras Staff Corps, for an Invention of
"AN IMPROVED RANGE FINDER OR INSTRUMENT FOR MEASURING AND
ASCERTAINING DISTANCES'
1
"
PROVISIONAL SPECIFICATION left by the said Francis Weldon at the
Office of the Commissioners of Patents on the 24th May 1883.
"
FRANCIS WELDON of Hale Crescent Farnham in the County of Surrey, Colonel
in the Madras Staff Corps,. AN IMPROVED RANGE FINDER OR INSTRUMENT FOR
MEASURING AND ASCERTAINING DISTANCES
"
This Invention has for its object improvements upon the Invention for which
Letters patent were granted to me bearing date April 9th 1879, No. 1416, and
consists in an apparatus or instrument for the purpose of ascertaining distances
by means of known and permanently fixed angles.
This is effected by a prism, the faces of which reflect the required angles, or by
a combination of prisms. When a single prism is used, it may be hexagonal,
reflecting three different angles, and secured in a suitable mounting. When the
required angles are shown by separate prisms, they can be combined in any case or
frame:
I use this instrument as follows:-
By means of one of. the prisms, I reflect the object the range of which is required
on a distant point, and mark the spot where coincidence is effected.
11.
I then advance in à straight line on the distant point, until a similar coincidence
is effected by means of another prism.
Thus a triangle is constructed, the base of which bears a known proportion to
one of its sides.-The length of the base, which determines the range, can be
ascertained by means of a third prism, with the advantage of compensating for
any possible error in the previous observations.
The advantages of this apparatus are simplicity, portability, and the accuracy
ensured by freedom from liability to derangement, to which other range finding
instruments are subject.

page_text: +17
SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said Francis Weldon in the Great Seal Patent Office on the
24th November 1883.
FRANCIS WELDON of Hale Crescent Farnham in the County of Surrey Colonel
in the Madras Staff Corps AN IMPROVED RANGE FINDER OR INSTRUMENT FOR
MEASURING AND ASCERTAINING DISTANCES
***
This Invention has for its object improvements upon the Invention for which
Letters Patent were granted to me bearing date April 9th 1879 N° 1416 and
consists in an apparatus or instrument for the purpose of ascertaining distances
by means of known and permanently fixed angles
.
1
This is effected by a prism the faces of which reflect the required angles or by
a combination of prisms-When a single prism is used it may be hexagonal,
reflecting three different angles and secured in a suitable, mounting, When the
required angles are shown by separate prisms they can be combined in any case or
frame.
Having thus far described my Invention I will now proceed aided by the
accompanying drawings to further and particularly describe same that is to say.
DESCRIPTION OF THE DRAWINGS
$
Fig 1 represents one form of my range finder closed. and Fig 2 Elevation
open.
Fig 3 Shows another form of instrument with three prisms arranged as shown.
The form of instrument shown in Fig 2. consists of two prisms one cut to reflect
an angle of 90° the other 88° 51′ 15″ such angle giving a base of as one is to fifty
the prisms being secured back to back in the circular case as shown.
To illustrate one method of carrying out my Invention and obtain the range
will describe same by reference to the diagram Fig 4.
Let it be required to find a distant object O from A
The observer places himself at A and looking through the lesser angle prism
moves until he sees ☐ covering P.
The lesser angle is now done with and the observer turns the instrument so as
to bring the right angled prisms into operation (and without moving from where
the first or lesser angle, was determined) the observer looking in the right-angled
prisins sees the reflected image of the point O, ie O¹ on the left of P.. The
observer will then go forward on the point of direction P until he reaches the
spot where he will see the fixed point O or distance point reflected on P. Thus
for instance if the lesser angle prism reflect 88° 51' 15 and the greater angle 90° the
distance between A and X will be one fiftieth of the range of the object O from
the point A. Or the process may be reversed by reflecting O upon P with the
greater angle first and marking point X Fig 1, and then retiring on the line X and
direction point P until by using the lesser angle, object O is reflected on P. The
length of the base X A may be ascertained either by direct measurement, or
by a third prism for the purpose of measuring or ascertaining shorter distances.
This form of instrument is shown in Fig 3. Three prisms are shown but more
than three may be combined if required
1
lit
Having thus described and ascertained the nature of my Invention I would
have it understood that I do not confine myself to the precise form of instrument

page_text: and angles of prisms but I claim as my Invention An improved range finder or
instrument for measuring and ascertaining distances substantially as herein before
set forth and described
In Witness whereof I the said Francis Weldon have hereunto set my hand and
seal this twenty second day of November in the year of our Lord one thousand
eight hundred and eighty three