Improvements in Distance Estimators or Measurers.
Year: 1891

page_text: Date of Application, 16th Mar., 189:-Accepted, 5th Sept., 1891
TOMPETE SPECIFICATION.
[Communicated from abroad by Hrco VON KROTTNAURER, Builder, and
HERMANN BETCHIE, Engineer, both of Berlin, Germany.]
Improvements in Distance Estimators or Measurers.
I, Hron DONALD FITZPATRICK, of 70 Wellington Street, Glasgow, Registered
Patent Agent, do hereby declare the nature of this invention und in what mer
the same is to be perforined, to be particularly described and ascertained in and by
the following statement :-
The subject of the present invention is an apparatus by the aid of which distances
can be estimated or measured quickly and safely and with sufficient accuracy for
military purposes.
This new apparatus, which is with regard to its general construction a telescope
or field-glass is distinguished by the application of divided objective-lenses .e. by
such an arrangement that a bar or line appears between the axis of sight of both
eyes and thus creates, in consequence a double picture.
It is found that the
nearer the object is to the observer, the nearer will the apparent picture appear to
the real object and as the distance increases so will the apparent picture appear
farther and farther off from the real object. By calculating this apparent increase
or diminution the distance of the object from the observer can be found with pretty
good accuracy, as the increase or diminution is in a fixed proportion to the distance
away of the object.
On enclosed drawing:
-
Figs. 1-6 show the new distance estimator or measurer in varied constructions
and in different positions, whilst Fig. 64 is a detail view.
With
The telescope is, in the example, given at Fig. 1. of the Dutch construction, but,
under this invention. both halves of the objective-glasses a' which are towards
one another are covered or darkened as shown at Figs. 1 and 4 so that every
objective will possess a sharply defined separation-line which will go through its
centre. A dividing line for both visual axes of the oculars is thus formed.
this arrangement, when the telescope (Fig. 1) is looked through, a double picture
of point is given. If the binocular is directed so that its right tube A points
to X the perpendicular separation-line of the proper objective a will be observed to
pass exactly through the middle of the point X, then, if the left tube A' is looked
through, the picture of the point X is seen, but it is not divided by the separation-
line of the ocular a', but the picture which appears in the position y lies on the side
of it, ie, on the side of the visular axis of this ocular. The dotted lines on the
drawings represent the visular axes.
If, now, the distance of the apparent picture y from the axis or separation-line of
the objective a¹ is carefully estimated, then this distance, when multiplied by the
Constant found, will give the real distance of the point X. In the example
illustrated in Fig. 1. the apparent picture y is at a distance of one millimeter from
the axis of the tube A and as the Constant is found to be 100, therefore the
distance of point X is 100 min.
This distance of 100 mm. is merely given by way of example as the instrument
would only be used for estimating considerable distances.
The greater the distance off that the point X is, the farther the telescope must
be pulled out and the farther away the apparent picture y appears from the real
object.
In Fig. 2. the point y is, as shown by way of example, at the distance of 2 mm.
from the axis; this is made apparent to the observer by the separation-line of the
objective of tube A', therefore the point X must be at a distance of 200 mm.
At 1,000 m. distance the apparent picture would be at a distance of 10 m. from

page_text: the visual axis. Side-deviations of this amount may be found up to a centimeter
after some practice.
The described telescope is principally designed for trained soldiers, to whom it is
very useful for estimating distances, as only mistakes of a few meters can be made,
and these errors need not be considered, when all that is required is to give a fairly
accurate idea of the distance of the thing observed.
It is not absolutely necessary that both objective lenses should be darkened or
that the half of the lens or lenses should be darkened, as the semi-darkening of
only one lens, causes the double picture required.
The application of the hereinbefore described instrument requires great practice
in estimating proportional small distances, and this practice everybody is not able
to give. To remove this draw-back the new telescope is, or may be furnished with
an indicator on which the distance to be ascertained may be read off without the
least trouble.
This arrangement may consist of a scale, which is drawn on a small piece of
glass (Fig. 1). The glass is fixed in tube A'. Or the arrangement may
consist of a scale B, which is capable of being slid down either behind or before the
objective lens a'.
By inserting the glass g between the objective lens and the ocular and so that
the scale is horizontal, it is evident that the position of point y can be read off
directly, but this method requires very good eyesight to prevent mistakes resulting
from the necessarily extreme fineness of the scale.
When a sliding scale B is used, the necessity for very good eye-sight is not
required, as in this case, it depends merely upon practice to be able to put the
scale B quickly and exactly on the apparent picture. The moving of the scale B
may be done, directly, by hand as shown at (Fig. 3) or indirectly as shown at
Fig. 2. by such means for example as a levers, which may be connected at one end
with the tube A by means of a pin joint or a link and at the other end be passed
through a hole in the scale B. As the scale B is pushed back and forward by the
rod the measurements can be taken; or the scale bar may be a plain one and be
provided with a finger or pointer and the frame of the objective lens be made with
a scale.
In either of these cases the degree of movement of the bar B can be
easily ascertained and as a result the distance of point X can be easily calculated
as before.
With these readings, however, the degree of accuracy is not very great
as the scale only moves. small distance when being adjusted and so the divisions
must not exceed a certain degree of fineness, if the reading is not to cause difficulties
again in the matter of eye-sight. Besides the moving of the scale by hand is not
accurate enough as an apparently very slight movement of it causes a considerable
difference when calculating the distance of the object.
To prevent these troubles I may arrange before the objective a' a slide B having
two racked arms (see Figs. 4. 4 5 & 6). The slide may be of glass so that the
objective is not darkened.
Between the ends of the tubes A, A' is fitted a spindle C which carries two
toothed wheels c c (Figs. 5 & 6) which gear with the toothed racks or arms bb
The spindle C has on its lower end a milled wheel C and on its upper end
friction-disc C made of indiarubber or its equivalent. Fitted over the spindle C
is a cone-shaped segment D carried by an arm d arranged in an easily movable
way. Against the lower surface of the segment works the friction-disc C2, whilst
on the upper surface is cut, for example, say a scale reaching from 200-2100 (sec
Fig. 4).
On the arm d a pointer or finger may be firmly fastened. If desired the
pointer need not be used, as the arm d serves to a certain extent as a pointer for
the scale.
With this arrangement when it is required to measure a distance, the right hand
tube A is so directed towards a remote object (say for example the point X Fig. 3
that the separation-line of the objective-glass a cuts the middle of the point X
Now by turning the spindle C the slide B is pushed so far before the objective a

page_text: that the division-line so produced appears on taking a view through the left
tube A' to cut the middle of the apparent picture of point X, at the position y
(Fig. 3).
But when the spindle C was turned the segment D was also turned and as the
pointer d' is stationary, it would therefore inlicate on the scale the amount of
movement or travel of the slide B. Now since the distance of the apparent
picture y from point X decides the distance of the point X from the spectator, as
already explained and as the slide B indicates the distance of the apparent
picture from point X consequently by having corresponding divisions on the
Segment D, one can read off at once the distance. Thus for example suppose the
segment was turned to the position indicated in Fig. 4 with the finger pointing
to the number 650, the observer would at once understand that point X was at a
distance of 650 meters. It has been found that the distance of the apparent
picture y from the point X is not the same for all eyes so that the instrument may
be correct for one observer and incorrect for another. To remedy this and to
make the instrument suitable for every eye, the segment D is so arranged as to be
morable in conjunction with an arm d fitted in the guide-piece E (Figs. 5, 6
& 6). This guide-piece is fork-shaped and between the jaws or prongs of the
fork the foot of the arm d can be moved forward and backward by means of
a screw e. If the segment D is fitted in such a way that the spindle lies in a
line with the turning-point of the segment (as shown at Fig. 6) then by turning
round the friction-disc C, the segment D will also be turned once round its axis.
But if the segment D is moved in its guide E so that the turning point of the
segment D, lies to the side of the spindle C (as shown at Fig. 5) the friction-disc
will work with a larger circle of contact. Thus for instance the distance between
the axes of the disc and the spindle may be such that it will be necessary to turn
the spindle C6 times to produce a single revolution of the segment.
The
segment D, when moving, is always in contact with the friction-disc as it is
pressed down by a small spiral spring fitted round a turning pin g' carried on
arm d or the arm & itself might easily be arranged to keep the segment always
pressed with sufficient force against friction-disc C. The guide E is at the same
angle as the angle of inclination of the segment.
The adaptation of the distance-measurer so as to suit the eye of the observer is
effected in the following manner :-
Direct the glasses to an object the distance of which (say 100 m.) is exactly
known, close the left eye and so direct the right hand tube towards the object
that the separation-line of the right hand objective cuts exactly through the
middle of the object or any prominent part of it.
Now close the right eye and
look through the left tube, care being taken when doing so, that the telescope is
not moved from its position. Then, by means of button C, turn the spindle C,
when the segment D will also be turned and the slide B will be pushed before
the objective a' of the left tube A, in the manner shown at Fig. 4ª. The observer
will now see distinctly a progressing dark limitation-line. The turning of the
spindle C should be continued until the limitation-line caused by slide B cuts the
point of the apparent picture y on which the right tube A was adjusted. When
this is done look alternately through the right and left tubes, compare the harmony
in position of both separation-lines, correct this position if necessary by turning
button Cand then investigate the distance the pointer d' indicates on segment D.
If the pointer indicates the number 10, then the position of segment D in guide E
is correct for the eye of the observer, and the instrument can be used by him for
finding unknown distances. But if pointer d' does not indicate 100 on the segment
then turn the screw e and move the segment, in its guide E, forward or backward
till, after repeating the above described test, the pointer d' indicates exactly the
figure 100.
Instead of using a segment D any suitable form of scale having good legible
divisions may be used for very great distances.

page_text: By darkening the objective lenses a a' the distance-measurer loses in width of
field and in consequence in usefulness as a simple telescope.
As hereinbefore explained the darkening of the objective lens a' is not necessary
for producing the double-picture and this glass a will therefore retain the proper
width of field if slide 13 is entirely drawn out. To also obtain this advantage for
glass a, it is only necessary to use a movable or hinged darkening cover for this
glass, such as is indicated on Fig. 2. In this figure the darkening is effected by
a hinged semi-circular leaf B which can be turned backward, and if turned high
up does not hinder the free view. When it is turned down it partly covers the
objective glass and thus renders the glass suitable for measuring distances, whilst
at the same time when turned up, it enables the glass to be used as a telescope.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed I declare that what I
claim is
(1) A distance-measurer consisting of a binocular or double telescope of which
one or both objective glasses are partly darkened for the purpose of producing
one or two sharp dividing-lines by which means the distance apart of the two
pictures of the object, which appear, when the tubes are looked through singly,
whilst the telescope is kept without motion, can be easily ascertained, substantially
as hereinbefore set forth.
(2) A distance measurer, such as described under Claim 1, so constructed that a
slide can be slid either before or behind one of the objective lenses, which slide
operates a segment, on which is indicated by means of a pointer the distance of
the object, substantially as herein before set forth.
Dated this 12th day of March 1891.
H. D. FITZPATRICK,
70, Wellington Street, Glasgow.