Improvements in or relating to the Estimation of Distances for Military Purposes.
Year: 1891

page_text: COMPLETE SPECIFICATION.
Improvements in or relating to the Estimation of Distances for
Military Purposes.
A communication from CASIMIR ERLE, of Vienna, in the Empire of Austria,
Manufacturer.
1, ALFRED JULIUS BOULT of 323 High Holborn in the County of Middlesex,
M.I.M.E., 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 :-
My invention has reference to a novel or improved form of apparatus for
measuring distances or finding ranges for military purposes together with certain
methods of making use of the said apparatus for the purpose of obtaining the oud
in view.
Like most other forms of apparatus designed for the same purpose it involves
the simple mathematical calculations included under the general designation of
"solution of triangles." But an essential feature of the present invention is that
it does not require the performance of any subsequent calculations but enables the
distances to be ascertained or read off at the same time as the observations are
made.
The apparatus forming the subject of the invention consists essentially of certain
appliances which are preferably attached to field-glasses or telescopes but which
may also be used independently.
The accompanying drawings serve to illustrate the construction of the various
parts,
Fig. 1 is a plan of one of the boxes or cases containing the angle mirrors,
which is attached to the object-glass end of the tube of the field glass.
Fig. 2 is a cross section of the same. It will be seen that the mirrors are 80
arranged as by their combined reflections to effect a deviation of the rays entering
the instrument from the side through an angle of 90° or nearly so.
It must be understood that' the box or case fitted to one of the field glasses.
differs in some respects to that adapted to the other. I will proceed therefore
first to describe the features which they possess in common. These are, 1. The
box or case open at one side, the top, and the end next to the object glass of the
field-glass to which it is attached, containing the mirrors set at an angle to
one another as mentioned above. This will in future be alluded to as the mirror
саве.
2. The bent arms or levers d and d pivotted at e, and prolonged beyond the
said pivot so as to form two shorter bent pieces d' and d. The lower arm dis
rigidly attached to the mirror case, the upper arm d' alone being capable of move-
ment about the pivot e. Its prolongation d³ is provided with a movable cam g,
pivotted at f, and working upon the other short arm d¹, in such a way that when
it is forced in a certain direction, it causes the two arms d and d to approach one
another. To attach the mirror case to the field-glass the cam g is turned up, and
the arms d and opened sufficiently to admit the tube of the field-glass. They
are then pressed down upon it and the cam y forced in the opposite direction which
operation clamps its arms d and tight to the tube of the field-glass and secures
the mirror case in position as shown at Fig. 3; the said cam g is secured in position
by means of the spring catch h. The top of the mirror-case is covered by a semi-
cylindrical tube i open at the end nearest d and partially closed by a diaphragm
at the other end. This semi-cylindrical tube slides in the grooves kk. The
diaphragm by which it is closed is perforated as shown at i and to enable' the
object the distance of which is to be determined to be sighted with accuracy. Each

page_text: mirror-case is further provided with a sight hinged at the use of which will
be explained in the sequel.
Peculiar to the mirror-case-I (which is used by the observer who takes up his
position to the left) is the frame cc which fits into two grooves in the bottom of
the mirror case. This frame, serves to support the divided scale l. Figure 4, which
may be slid backwards or forwards in the groove in which it is held. This scale
is subdivided in a special manner which will be explained later, and is provided at
either end' with a sight's and s
Figure 5 shows a method of attaching the instruments to stands or tripods
which enable greater accuracy to be attained but are not however indispensabile.
For this purpose there are two cylindrical channels or tubes m m parallel to the
direct sighting line arranged for the reception of the two parallel pins n n of the
mirror supports. It is by these pins that the mirrors may be connected with any
suitable stand preferably consisting of a post or support upon which rests a dove-
tailed or grooved guiding bar o wherein a carriage is adapted to slide. This
carriage is provided with one of the so-called Hooke's joints and the connections q
and r.
.
Figures 6 and 7 are diagrams showing the positions of the observers and the
mutual relationship of distance of object, base of operations, and divided scale.
While Figure 8 shows the positions of the instruments and scale when observing
a point O, dotted lines shewing the requisite displacement of the slide for a more
distant object O
Supposing that two similar reflectors were employed we might ascertain. the
distance of an object O, Figure 6, as follows,
One of the observers whom I will designate A would attach the mirror-case I
to his field-glass in the manner described above. He would then insert the divided
scale into the frame designed for its reception as shown in Figure 8 and take up
his position at I, Figure 6.
The second bserver whom I will designate B would also attach his mirror-case
to his field-glass and turn down the sight and giving one end of a measuring tape
to A, who would peg it into the ground, proceed to walk away from him in a
direction approximately at right angles to the line I O, until he had unrolled a
certain fixed length of the tape-say 40 yards-A meanwhile observing the object (
directly through his instrunient, and signalling to B by movements of the band
that he is to move forwards or backwards until the reflection of the sight on his
instrument is seen by A to coincide with the object O. Observer A then knows
that the line III ie. the line from him to observer B is at right angles to the
line 10 whereupon he signals to B to remain where he is.
Observer B then proceeds to sight the object directly and the divided scale on
instrument I at right angles to him by reflections in the mirrors of his instrument.
He then signals to A to move the scale backwards or forwards until the back
sight & is seen to coincide with the object, when he gives him a sigual to cease
moving the scale. The distance on the scale from the sights to the index point
in the frame c (which represents the centre of the instrument) may then be read off.
Now it is obvious from the principles of elementary geometry that the
triangles III S, and IO II are similar triangles, and therefore the base IS is to
the side I, II, as the base I II is to the side I O.
If therefore we always operate with the same length of base I II, multiplying
the readings on the divided scale by a certain constant will give the distance 0.
To facilitate the measurement and render calculation unnecessary the divided
scale is so made that this constant is 100 e. 10 of its divisions correspond to a
distance. I 0 of 1000 yards. If therefore in the above instance the reading were 25
the distance of the object O'would be 2500 yards.
In practice however for estimating with rapidity distances such as are generally
involved in artillery practice-say 1500-3000 yards-I prefer to proceed in a
slightly different manner.
In this case the arrangement of the instruments is as follows.--The angle mirrora

page_text: in instrument [ are arranged at the same angles as before that is to say in such a
way as to reflect an object exactly at right angles to the optic axis of the field
glass to which the instrument is attached. In instrument II however the mirrors
are arranged so that the direction of the reflected object (the sight of the other
instrument) does not form exactly a right angle with the optic axis of the whole
instrument. On the contrary it makes a somewhat smaller angle-say 88° 51' 14:7”-
or the complement of an angle whose arc is therewith. Then there will be a
certain distance for O at which, with the base of 40 yards between the observers,
observer A will find that the reflection of B's sight .coincides with the object O,
while B will find that in his case the reflection of the zero point of the divided
scale attached to A's instrument will coincide with the object O. The distance I O
at which this takes place will, in the given case of base III 40 yards and
<01-188° 51' 14:7", be 2000 yards, and I therefore call this distance of
2000 yards "normal distance."
=
Suppose now that the distance be less than 2000 yards, then the point on the
divided scale which B will find to coincide with the object will lie to the rear of I.
B consequently signals to A that he must turn the back sight up into position and
commence to move the scale in or out (according as signalled by B) until the
reflected image of the back-sights coincides with object. The distance separating
the said sight from the zero point is then read off. Let us suppose it to be
5 divisions, then as every division on the scale represents 100 yards the distance
of O will be 500 yards less than 2000 yards viz. 1500 yards.
Similarly let it be supposed that the distance I O is greater than 2000 yards,
then the point on the divided scale the image of which will be found by B to
coincide with the object O will be situated in front of I. B accordingly signals
to A to turn up the front sight and move the scale in or out as before when the
distance on the scale from sight to zero point is read. Suppose that it is found
to be 7 divisions, then the distance of O will be 700 yards more than 2000 yards
we. 2700 yards.
'
In cases of emergency that is to say where great. rapidity rather than accuracy
is required in finding the range or measuring the distance I O, I. proceed as
follows, (see Fig. 7).
I remove altogether from instrument I both the divided scale and the frame o
by which it is held in position, while the sight of the instrument is turned
down so as to be visible to the other observer. Observer B then walks away
from A in a direction at right angles to the line joining observer A and the
object (this direction being ascertained as in the former observation), until he
finds the reflected image of the sight on instrument I coincides with the object O.
The distance between the observers is then measured with the measuring tape.
Owing to the great length of IO compared with the base 1 II, and the smallness
of the amount by which O III differs from a right angle, the whole triangle IO II
may without sensible error be regarded as a sector of a circle and the base I II
AB An arc. Now in the present case the angle IO II is such, owing to the set
which has been given to the mirrors of instrument II, that I II O I, or in
other words the base is 3th of the distance, from which we get the rule "half
the length of the base III in yards gives in hundreds of yards the distance of O."
Of course if necessary the triangle III may be solved by one of the usual
methods and the distance 1 O ascertained in that way. But time is of course saved
by proceeding as above and using one of the instruments with its mirrors set to the
angle mentioned.
=
50
am aware that angle-mirrors for ascertaining the position of points at right
angles to one another are already in use.
Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is
1. The arrangement of parts consisting mainly of the bent arms d and ď

page_text: with their prolongations and Figures 1 and 2 together with the cam g
serving to attach the mirror-cases to the field glasses as shown and described.
2. The use and arrangement of the divided scale Figure 4 attached to instrument I
as described and the employment of the same and the sub-divisions with which it
is provided in combination with the other appliances for the purposes of estimating
distances essentially as shown and described.
3. The arrangement of the mirrors in instrument 1 so that the direct and
reflected rays form right angles with one another and the arrangement of mirrors
in instrument II in such a way that direct and reflected rays form an angle slightly
less than a right angle viz. an angle 88° 51' 14.7" for the purpose of facilitating
the estimation of distances in the manner shown.
4. The different methods of using the above described apparatus and appliances
or combination of appliances in the manner and for the purposes described.
Dated this 13th dow of July 1801
W. P. THOMPSON & BOULT,
Agents for the Applicant.
W. P. THOMPSON & BOULT,
Agents for the Applicant.