Year: 1886

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I, FRANCIS WELDON of Erlimount Earley, in the county of Berks, Colonel in
the Madras Staff Corps, do hereby declare the nature of this invention and in what
manner the same is to be performed, to be particularly described and ascertained in
and by the following statement:―
The object of my invention is a measuring line or tape to be used in combination
with the range finder which forms the subject of my Letters Patent bearing date
24th May 1883 and numbered 2589.
.
In the accompanying sheet of drawings Figure 1 is a diagram representing the
mode of measuring a range by means of my aforesaid range finder, and Figures
2. 3. 4 and 5 are representations of my improved lines or tapes to be used in
combination with the said instrument.
The mode of measuring a range is described in the specification of my aforesaid
Letters Patent No 2589 of 1883, but in order clearly to explain the use of my
present invention, I will again briefly describe the operation by reference to
Figure 1. Let it be required to find the distance of any given object O.
The observer, standing at A, by means of the lesser angle prism in the instru-
ment, reflects the image of O upon any convenient distant object P, the point A is
then marked by a picket and the observer turns his instrument to bring the larger
angle prism into use. He then sees the image of O reflected at a point O' to the
left of P, and advances on the line A P until he arrives at a point X, where the
image of O again coincides with P. The point X is marked with a picket.
The above process may obviously be reversed; thus the observer commencing
at X reflects the image of O upon P with the larger angle prism, then marking X
and using the lesser angle, he sees O to the right of P and retires backward
along PX until at A, the image of O again coincides with P. In practice this
latter method is the one usually employed. A triangle OA X is thus obtained of
which the angles O AX and OX A are known and of which the base X A can be
measured. In the form in which I usually prefer to construct my range finder,
I cause the one prism to reflect an angle of 90° and the other an angle of
88° 51' 15" as shown in Figure 1.
These particular angles are found convenient because they give a proportion of
1 to 50 between the sides A X and X O, so that every yard on AX represents a
distance of 50 yards in the range ✗O. I therefore divide or mark my improved

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measuring line or tape on the scale of 1 yard 50 yards and in practice usually
mark it in divisions, which each represent 10 yards of the range. Figure 2
represents a line marked off in such divisions by small labels affixed thereto and
bearing the required numbers. Figure 4 represents a tape marked off to a similar
scale. To ascertain the range X Ŏ it is therefore only necessary to lay the tape
or line upon A X and at once read off the range without any calculation being
required.
When the range XO is a very long one it may become inconvenient to directly
measure the base AX, I therefore usually construct my range finders with a third
prism reflecting an angle of. 74° 53' 15" and the observer standing at A, retires
backwards along the line OA until he reaches a point B where he sees in this said
third prism the picket X reflected on O along the line B A O. This short base A B
is one quarter of the base A X and is therefore one two hundredth part of XO,
.and I measure this second short base by means of a line divided on the scale
of 1 yard
200 yards as shewn in Figure 3 or of a tape similarly divided as
shewn in Figure 5.
=
In practice I prefer to use the tape and in this case I mark one side of the tape
on the scale of 1 yard 50 yards and the other side on the scale of 1 yard = 200
yards thus combining the two scales and making a very convenient and portable
instrument.
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I do not necessarily confine myself to the use of tapes or lines, as I may use
rods, jointed or otherwise constructed, and marked or divided in the required
manner. Nor do I confine myself to the particular scales described, as if the
prisms of the range finder are made to reflect other than the angles mentioned, the
divisions on the measuring tape must necessarily be made to a scale to correspond
therewith.
It is obvious that the range finder or similar instrument in connection with,
which my said measuring device may be used, need not necessarily be of the same
construction as that described in my patent No 2589 of 1883.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed I declare that what
I claim, is :-
(1.) A measuring tape, line, or rod, marked or divided, substantially as herein
shewn and described, for use in connection with a range finder or other similar
instrument.
(2.) In a measuring tape for use in connection with a range finder or other
similar instrument, the combination of two scales of markings or divisions on the
opposite sides thereof, substantially as herein shewn and described.
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