An Automatic Distance-measurer.
Year: 1893

page_text: Date of Application, 19th June, 1893
Complete Specification Left, 14th Mar., 1894-Accepted, 28th Apr., 1894
PROVISIONAL SPECIFICATION.
An Automatic Distance-measurer.
I, WEBB GILLMAN, Lieutenant in the 29th Field Battery, Royal Artillery,
at present quartered at the Royal Artillery Barracks Clonmel in the County
of Tipperary in Ireland do hereby declare the nature of this invention to be as
follows:-
The distance AO (shown in the annexed figure) of an observer at a station, A,
from a remote object, O, is by means of this invention determined at once by a
simple observation, and without any such measurements as of a base line, or of
any angle.
This end is attained by an instrument (in any of the forms below mentioned)
which automatically directs a line of sight through a fixed point C, in space, at a
fixed distance of 1 to 10 yards, or more, to the right or left of the line of sight, AO,
from the observer to the remote object, and at a fixed distance of 25 to 100 yards,
or more, from the observer towards O, but without the necessity of the observer
proceeding to this point C, or otherwise exposing himself than about the point A.
The above mentioned simple observation consists, after the instrument is duly set,
in moving a pair of sights, or a small telescope, B b,-so arranged in the instrument
that the line of sight, Bb, shall always pass through the fixed point, C-till this
line of sight, B6C, falls on the remote object O: thereupon the distance, AO,
may be at once read off on a scale which is marked on some suitable part of the
instrument.
The line of sight, BC, is, by this invention, after the instrument is duly set,"
determined to pass always through the fixed point, C, by any one of the following
alternative methods, or instruments, all of which, as well as the automatic deter-
mination of the fixed point C, in space, at a distance from the observer, I believe
to be wholly rew, and for which I apply for a Patent.
1st. By attaching a sight line, or small telescope, B6 perpendicularly to a collar
sliding along an arc of a circle of radius 25 to 100 yards, or more, as found most
convenient, which arc is suitably connected with the instrument.
2nd. By a combination of seven small bars in a linkage, jointed similarly to that
known as 66
'Peaucellier's linkage for drawing a straight line," but differing
therefrom in at least two new particulars viz. (a) The inverse curve is not a
straight line, but a circle of the required radius, which requires a special new
arrangement of parts, and (b) additions are made to the linkage which make use of
a certain mathematical property of inverse curves, and ensure the line Bb (added
to the linkage in a novel manner) always passing through the fixed centre C of
the said circle.
3rd. By the equal revolution of two spindles having unequal screw threads
differing in a fixed ratio, or by the unequal revolution of two spindles having equal
screw threads, these spindles having nuts bearing sights, B, and, b, and moving as
the spindles revolve in such a manner that the line, Bb, shall always pass through
the fixed point C: or by a linkage with or without screws effecting the same
object.
This invention has the following new advantages :-
It secures great speed in range-finding and reduces the exposure and movements
of the rangetaker to a minimum; and thus conceals him from an enemy: it obviates
the need of any measurement, on the ground, of a base line or of any angle, and
thus eliminates a fruitful source of inaccuracy: The length suitable for graduation
in the instrument may by this invention be a large length of several inches, or

page_text: even feet, and does not involve micrometric graduations; and also this length for
graduation can itself be indefinitely multiplied by a drum, or any other common
and usual contrivance.
"
The portability of the instrument in any of its forms may be secured by the
folding of its parts, and by the use of lightly constructed rods on the "lazy-tongs
principle and much economy is gained by the very simple nature of the instrument
in any of its forms and by its non-liability to become out of order.
Dated, at Clonmel, this 16th June 1893.
WEBB GILLMAN,
Lient. R.A.
An Automatic Distance-measurer.
I, WEBB GILLMAN, Lieutenant in the Royal Horse Artillery, of Clonteadmore,
Coachford in the County of Cork, now stationed at Meerut, in India, 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 :-
1. The effect desired is to provide a simple instrument whereby the distance of
a remote object, as O (Fig. 1.), from an observer at A, may be easily & speedily
ascertained.
The principle adopted for attaining this effect is as follows:-First, the direction
of the line AO (Fig. 1.) is fixed by setting a bar carrying a telescope, or sighting
instrumentalities, to point from A to O; next, a line A D B₁ is supposed to be set
out making any angle-(no particular angle being essential)-with A O, and a
fixed length A D is assumed thereon; and a line DC is supposed to be set out
from D parallel to A O, and of a fixed length. Then, if an observer, standing near
B', observe where his line of sight B'CO-passing through C to the object O
cuts the line AD B¹, he can at once find the distance, or range A O, by measuring
the length D B'; (in this instrument the ranges are marked on a scale near B¹, as
hereafter described), for, from the similar triangles OA B' and C D B' we have

page_text: 2. In the above mentioned construction, supposed to be made on the ground, i.e.
the setting out of the lines AD and DC, it is obvious that the result is merely the
fixing of the poiut C, for the purpose of directing the line of sight B'CO: and
the intent of the present invention is, inter alia, to automatically fix this point C in
space, and direct the line of sight, B'CO, through it, without the observer having
to proceed to the point C, or to measure the length DC at all. This length DC,
(which may be of any desired length, or of various lengths,) being thus automatically
fixed, acts as a measured base, but the actual measurement itself is obviated.
Throughout the figures and descriptions following, A a means a telescope,
whose axis is Aa, with eye-piece at A; or it means a bar, whose central line
is A a, with a back sight about A and a front sight about a Dd means the
central line of another bar, set parallel-to A a by means hereafter described: and
the fixed point C is always in the prolongation (supposed) of Dd: and B and b
are a front and back sight respectively, or, the line Bb is the axis of a telescope,..
attached to parts of the instrument which are themselves connected with the .
bar Dd, B and being points in the line of sight B'CO before mentioned, which
sight-line may therefore be described as B b.
In the figures only the essential parts of the instruments are shown.
The sighting instrumentalities may be a telescope, or sights similar to those of a
"plane-table-sight-rule"; these latter suit all forms of the instrument very well.
I do not, however, restrict myself to the use of these solely, or to that of a
telescope. Further, any numbers & lengths given in the following descriptions are
by way of illustration of principles by particular cases, and not as the only numbers
& lengths admissible in the instruments.
3. The sight-line, Bb, is, by this invention, determined to pass always through
the fixed point C by any one of the following alternative methods, each worked by
a suitable instrument, all of which, as well as the automatic determination of the
fixed point C in space are believed to be wholly new :-
1st Method. The attachment of a sight-line, or telescope, Bb, perpendicularly to
a collar (Fig. 2.) sliding along an arc of a circle, whose radius is equal to the
required length DC, this arc being connected to the bar Dd at the point D, and
the line Dd being part of the radius DC of the circle. The arc itself may be
constructed by finding the co-ordinates of successive points on it with reference to
the line Dd, and a perpendicular to Dd at D; or, the arc may be drawn at once
by a linkage as described-in the next method. This form of the instrument is
portable, the arc folding back into the bar Dd.
4. 2nd Method. A linkage similar to that well known as "Peaucellier's linkage
for drawing a straight line," but differing therefrom & having sundry new
additions thereto, which may be thus described :-
At d, a point in the line Dd, (Fig. 3.) are pivoted two equal links dp and d p',
whose other ends are also pivoted at the points p and p' of a rhombus B pg p¹ com-
posed of four equal links Bp, pq, qp¹ & p¹ B, pivoted together at their four angles.
If the point q be made to describe a circle, with a radius Eq, round a point E
on Dd, then, as is well known, the point B will describe a circle which is the
"inverse," with reference to the point d, of the circle described by point q: and
by properly choosing the lengths shown in the figure, the radius of the circle
described by B can be obtained of any desired length, and the centre of this circle
will in all cases be in the line Dd, or this line produced.
For the proper choice of the lengths of the various rods in this linkage, I proceed
thus, The formula connecting the radii of the two circles can be found by a
simple mathematical calculation, and the result is

page_text: u is the radius, E 9, of the circle 'described by
t is that of the equal links dp and d p'; and
rhombus B pq p²:
round E; is the length* Ed;
s is that of each side of the
Another formula connects u and v and the length of line D d, i.e.
-
=
Now, when B is at its initial position at D, and t and s in positions t¹ and s¹,
the rhombus should be in as compressed a position as the nature of its connections
will admit so as to give B as large a path to the side as possible. So, if, in
continuation of the above example, its short diameter in this position be about
inches, then will u + v be about 45 inches; and we start by assuming u to be
slightly over half this latter (say) 60 times 38 in., that is 22-8 inches, whence
by formula (IV), v will be 59 times 38 in., that is 22-42 inches, & u + v =
45.22 inches; and if these values of u and v be substituted in formula (III), then
(being 240 feet) we get a numerical value for t-s²; and then assuming t + s
to be (say) 72 inches (i.e. when the rhombus is at its extreme elongation so as to
give B a large swing to the side,) and dividing this value into 2 - s² we get t
and, as a final result, t = 51.07 inches & s = 20.93 inches. In this way, by the
help of the two formulæ (III) & (IV) and by two choices of figures, we get any
values required of the four unknowns, u, v, t and s for any known r and Dd.
-
The above indicates how the point B can be made, by this linkage, to describe
a circle of any desired length of radius, DC, whose centre is in the prolongation
(supposed) of Dd. It remains only to explain how a sight bar Bb can be made
to move always perpendicular to the tangent of this circle at B, and thus point
always, in every position of B, to the fixed point, C, the centre of that circle.
This is easily accomplished thus :-It is known that the tangents to this circle
and to that whose centre is E, at the corresponding points B and q, make equal
angles with the vector dq B; hence the perpendiculars to those tangents must
also make equal angles with the same vector; and, as is evident from the symmetry
of the figure, those perpendiculars meet on the diagonal of the rhombus pp¹.
Hence, for proper direction of the sight-bar Bb, it is only required to pivot one
of its ends at the point B, and to have a slot at the other end, about b, which
shall run on a pin standing vertically up from a collar sliding along the radius E
produced, a pin being also produced downwards to run in a slot on a bar pp¹
१
pivoted at p and sliding through a ring on the pivot at p. It is found that
this arrangement works very smoothly; and it ensures the sight-line Bb pointing
in every possible position to the point C fixed in space.
Moreover, by a slight alteration in the point E, effected by a micrometer
screw not shown in the figure, the length DC can be altered as desired; and
as DC performs the part of a measured base-line, it follows that this base-line
can be at once altered, at will, to suit the finding of longer or shorter ranges.

page_text: For portability the bars t, t, are made detachable from the pivots at p and p²,
and these bars and the rhombus (elongated) fold on the bar D d, and the whole
can be carried in the hand.
5. 3rd Method. A frame attached to the bar Dd, or a bar opening out from
it by "lazy-tongs" attachments, having two parallel spindles, with screws of
equal, or unequal threads, revolving in such manner that the line, (Bb) joining
nuts working on those screws, shall always pass through a distant fixed point C
on the (supposed) prolongation of Dd, the principle of which is as follows:-
Fig. 4, shows in outline such a frame, or pair of parallel bars, DF fd, the
parallel screws being DF and df. If, to fix ideas, the length DC be 240 feet,
and Dd between the axes of the screws be 4 feet, then it is obvious that if, as
the screws revolve, their respective nuts B and 6 move from Dd so as to make
always the proportion of the length D B to the length db as DC is to dC, or
as 240 is to 236, or as 60 is to 59, then the line Bb if produced would always
pass through C, as is evident from the similar triangles C db, CD B.
This proportional movement of B and can be effected in either of two ways;
the first being that where the threads of the two screws are exactly equal, and
where, for one revolution of the screw D F, the other df makes 28ths of a revolu-
tion; and this is managed by putting at F a wheel with 59 teeth, and at fone with
60 teeth, (to suit the numbers above chosen for example,) these wheels being
connected by a fusee chain with holes gearing on the teeth. By this means for one
revolution given to D F by the observer's hand, d f will be turned 8th of a
evolution, and the length traversed by nut 6 will bear that proportion to the
length traversed by nut B; and thus the sight-line B b will always pass through
the point C, fixed in space, in the (supposed) prolongation of D d. The second
way of effecting the same end is by cutting the screws so that there may be
(e.g.) 59 threads on D F in the same length as 60 threads on df; in this method
the wheels at F and have an equal number of teeth.
For portability, the spindles are detachable from their sockets at D, and d, and
the bar &c. at Fffold by the "lazy-tongs" up against the side of D d.
:
As
Another form of this method is shown in Fig. 5. Here the nut on the
screw D¹ F is fixed, & is part of the bar D d thickened to receive the screw.
this screw revolves, the end F recedes from D', carrying with it the bar B &¹
always parallel to D d, guided by the "lazy-tongs" arrangement shown in the
figure the length B on this bar is equal to Dd, (say, for example, 4 feet,) &
suppose D C to be 240 feet. At 1 is a socket in which works a spindle, fb, having
a screw cut on it in the part outside the bar B. On fb is a nut 6 carrying a pin
which works in a small slot in a light bar Bb pivoted at B to B and acting as
the sight-line B b. Now if, as the screw D' F revolves, (turned by the observer's
hand,) making a certain distance traversed by the bar B from D d, the point b
of the sight-bar Bb be made to recede from 6' towards d through a distance equal
to one-sixtieth of the distance inade between the bars D d and B 1, (in above
example,) then will the distance db be 88ths of D B, and B b will point, throughout
to motion, to a point, C, 240 feet from D in the line Dd (supposed) prolonged. And
this is accomplished, as before, in two ways:-1st by having equal threads on the
screws D Fond fb, and by wheels at F and f, as before, but causing the screw f
to revolve once for 60 revolutions of D' F; or, 2nd, by cutting the threads of the
screws so that there are 60 threads on fb in the same length as one thread on D' F.
In this latter case the wheels at F and fare equal.
For portability, the screws are detachable from their sockets, and the bar B b
folds into B, & both fold against D d.
6. 4th Method. A simple linkage of four bars, pivoted together, and forming a
parallelogram with two opposite sides produced, which I call the "four-bar-
linkage.'
Fig. 6. shows this linkage. At D and d, on the central line of the bar D d, are
pivoted two other bars D B and db; below these latter, at points H and h on their

page_text: -central lines, there is pivoted another bar or link H h, the length of which between
the pivots H and his exactly equal to the length D d, and the distance D H is
exactly equal to d h. Thus DH hd is a parallelogram; and, whatever angular
movement be given to the bar D B round D, (either by the observer's hand, or by
-a screw for smoothness of motion,) an exactly equal movement will be communicated
to db round d, and D B and db will be always parallel throughout such movement.
If (to fix ideas) we require the length D C to be 240 feet, & take D d to be 4 feet,
then, if the points B and b be so chosen that the length D B bears the proportion
to db that DC does to d C, that is, as 240 is to 236, or as 60 to 59, the sight-line
joining B, b, will always pass through C, however the bars be moved.
Further, by simply altering the length D B, (which may be done by a micrometer
screw, or by various holes in the bar D B for the back sight at B,) the length DC
can be immediately altered to any extent desired: and, as D C acts the part of a
measured base-line (though no measurement takes place), this easy alteration of
such base is very advantageous in suiting greater or less ranges.
For portability, the pivots at H and are detachable, and the links D B and d b
then fold in upon bar D d, along which H h can also lie. This is a very light,
simple and portable effective form of the instrument, easily carried in the hand or
as a lance is carried by a horseman. Any parts of it, except the sights at B and 5,
can be replaced by an ordinary artisan.
7. The methods, above described, show, in four alternative ways, how a sight-
line B b, which has to be directed to the object, O, (Fig. 1.) can be so arranged as
to pass also through a point, C, automatically fixed in space in the (supposed)
prolongation of the central line of a bar D d placed in front of the observer. But,
further, the process of finding the distance AO (Fig. 1.) requires that the line D d
shall be parallel to the sight-line A a when pointing to O. The method of ensuring
this parallelism of A a and D d varies according to two classes of the instrument
Class I. That in which there is a rigid connection (not designed for easy
portability,) between the bars A a and D d, so that D d follows the movement
of A a and remains always parallel to it as the latter is being pointed to O. This class
is suitable for fixed positions, such as forts, fixed batteries, or on board ship &c.
Class II. That in which the means used to set D d parallel to A a is of a
portable nature, suitable for carriage in the hand, &c.
8. In instruments of Class I, where the portability of the means of parallelism
between A a and D d, described below for Class II, is unnecessary, (though not
unsuitable for this Class I, also,) a connection between the bars A a and D dis
made by two stiff parallel rods, as shown in Fig. 7. J J' are the ends of a light
platform capable of being sloped, round its axis J J, so as to bring the platform
At one end of its
into one plane with the object whose distance is to be found.
central line J J', A. a is pivoted at its own middle point, M; and D d is similarly
pivoted, at its middle point, M³, to the other end of the platform, so that both
can move angularly round those points in the plane of the platform. Further,
two stiff equal rods K K' and L'L' are pivoted to points K, L, of A. a, and
points K, L, of D d, these points being such that the length K L is equal
to KL, and that K and L are equi-distant from M, and K' and L' equi-
distant from M¹; and the length K K is equal to L L. Thus K K L L is
a parallelogram in every position it can assume as A a and D d turn round their
mid-points. Also, to steady the motion of this parallelogram, three or more
cross links, parallel to A a and D d, are pivoted at their centres at equal
distances along the line J J', and at their ends to the bars K K' and L L'
respectively, the lengths between their end pivots being equal to that of K L
or K L. Thus, whatever angular movement be given to A a round its middle
point, M, in being pointed to O (Fig. 1.), an exactly equal one will be com-
municated to D d round its middle point M. This angular movement is given
to A a simply by the hand, or by a spindle fixed on the platform & rotated

page_text: by the observer's hand and having a screw near its end under K K' acting in.
teeth on the under side of that rod, and an equal screw at its other end
over L L and acting in teeth on the upper side of that rod.
✓ The process of finding the range of a distant object, O, by this instrument
is simply this :-
--
The observer first points the sight-line A a to the object: this operation sets D d
parallel to A a. He then points the sight-line Bb to the same object, whereupon.
he can at once read off the range on the graduated scale of the instrument.
In Fig. 7. where, for illustration, method No. 4, before described, is shown in
operation, the range appears on the bar BT parallel to the line J J', (or A D, Fig. 1,)
as described infrà.
Thus the operation consists in merely pointing two sight-lines A a and B b.
Buccessively to the object, which occupies only a few seconds of time and only one
observer is required.
Notes: This instrument finds the range of a moving object as well as of a fixed
one; but two observers are needed in this case, one to observe the object through.
the sight-line A a simultaneously with the other observer sighting it through Bb.
Also, this instrument is adapted for finding the range of a fixed, or movable light
at night, the only addition needed to it being spots of luminous paint on the frames
supporting the wires of the front sights a and b. Also, this instrument finds readily
the mutual distance of two remote objects. The only addition needed for this is a
graduated semicircle, whose centre is that of the pivot at the middle point, M, of A a,
so as to show the angle made by A a between its two positions when pointed
successively to the two objects. This angle and the two ranges being known, the
mutual distance can be found by help of a pair of graduated rods, one of which may
be the central line A a, the other rod opening out from it like the arm of a drawing
compass. When these rods are opened to the angle shown by Aa on the arc, and
the found ranges are set off at the proper points of the rods respectively, the distance
between these points, measured on a graduated card or rod laid across them, is the
mutual distance required.
:
9. Class II, is that form of the instrument where the means used to set Dd
parallel to A a is easily portable. In this form, the bars A a and D d are made
capable of being mounted on tripod stands, and rest stiffly in chairs thereon, which
are capable of being rotated horizontally round a vertical dowel in the head of each-
tripod stand and in these chairs the bars themselves can have a slight movement,
vertically, so that they can be brought into one plane with the object. Fig. 8. shows-
a cross section and a side view of such a chair; each bar can rock vertically on pins
which drop into notches in the sides of the chair, a button then securing the pins from
rising out of the notches during the process of observation. The bars A a and D d
have thus a full horizontal motion, and a sufficient vertical one, for their needs. The
dowels are vertically under the middle points of A a and Dd when mounted on their -
chairs.
In this class, the connecting rods K K' and L L' of Fig. 7. are made in sections,
each of which may be two, or two & a half yards long, of such material as light-
steel tubing, the end of one section fitting into a socket in its adjoining section and
being held therein by pins in the cross rods. The central cross rod has a hole at
its mid point, which fits, for support, on a dowel in the head of a tripod stand placed
underneath it after the tripods under A a and Dd are pitched. Another & even.
more portable form of this connection is shown, in outline in Fig. 9. It consists of
two sets of "lazy-tongs" which fold up into a small compass easily carried. The
nodes of the tongs are joined by cross rods, as before, fitting on pins at those
nodes; or, the centres can be so joined at the middle points of short cross diameters.
made movable a strong arrangement is got by so joining centres and nodes shifted
so as to be opposite.
:
13 The process of finding a range with this class of instrument is exactly
similar to that before described for Class 1. (par. 8.) after the bars A a and D d`
are mounted on their stands; and this class shares all the advantages of the other.

page_text: "
Another, and still more portable form of this class of the instrument is shown
in Fig 10; and it admits of any desired distance being taken between A a and Dd.
In this, after the bars A a and Dd are mounted on their respective tripods, a steel
tape. of (say, to fix ideas,) 10 yards long from centre to centre of rings at its ends,
is put on pins at the mid points M, & M' of those bars. The tripod stands are then
pitched so that the tape is fairly taut, and the tape is then cast off & wound up.
The stands are then ready for taking any number of ranges of objects in front of
them; no shifting of the tripods being necessary for taking different ranges from
oue position. The following addition, which I call the "adjusting-four-bar-linkage
is made to the bar Dd:-A small sight-bar, M'n', of (say) one foot long, having a
point M on its central line on the axis of the dowel on which Dd revolves
horizontally on its tripod head, is pointed to M on A a, after A a has been pointed
to the object, and then M'n' is clamped in that position: at its end n' there is
pivoted a light bar n' P kept always parallel to Dd by a cross bar QQ equal in
length to M'n', and so fixed on pivots as to make Q Q'M' n' a parallelogram in
all positions: another small sight-bar DP is pivoted at D making length D M Ma,
a being a pin standing up from bar A a; and the end P has a small slot running
on a pin P on Pn¹. The length Pn' is to length D M' in the proportion of 14 to 15,
(when M M' is 10 yards, as above chosen for example,) so that, in every position
of the parallelogram QQ'M' n', the sight-bar DP will always point to the
middle point of the line M M', (i.e. 15 feet from M' when M M' is 10 yards long).
-
To take a range with this form, the process is simply this:-A a is pointed
to O; M¹ n' is then pointed to M and clamped. Then Dd is rotated horizontally
round its dowel at M till the sight bar D P (carried with Dd) points to the pin a
on A a; this sets Dd parallel to Aa, (the lines M M' and Da being then
diagonals of a parallelogram of which Ma and D M' are opposite sides). It
only remains then to point the sight-line Bb, as before, to the object; and the
range can be at once read off on the graduated part of the instrument.
The
This form shares all the advantages of Class I before stated.
linkage D P n' M', for portability, folds in on bar D d, or can be detachable. To
find the range of a moving object (night or day) with this form, three observers are
required, one to keep A a pointed to the object, a second to follow point a with the
sight-line DP, & the third to sight the object through Bb, all working
simultaneously.
Another plan for setting D d parallel to A a is that which I call the "movable
triangle." It is shown, in outline, in Fig. 11. In this, a small sight-bar n' M'S'
is movable, and has on its central line a hole fitting either on a pin at M' on
bar Dd, or on a similar pin at M on A a, (shown there in position n M S). At its
end S¹ is a screw which can clamp a light brass bar R'S' at any point of the length
of this bar, whose other end R' fits on a pin at R' on D d, or on a similar pin R
on A a. This triangle has sides exactly equal in its two positions, RSM and R'S M'.
It is used thus:- After A a and Dd are planted on their stands and A a is pointed
to the object, the triangle is put on the pins, M, and R, on A a with the screw at S
loose; then the sight-bar S Mn is pointed to the pin M' on Dd, & the screw at S
is tightened the triangle is then lifted off A. a, & is carried to Dd & placed thereon
in position R¹ S₁ M³, (i.e. reversed through two right angles from its previous
position on A a,) and Dd, carrying the triangle, is then rotated round its dowel
at M till the sight-bar. S' M' n¹ points back to pin M on A a. When it so points,
Dd is parallel to A a (because the alternate angles R M S and R' M' S¹ are
equal).
This plan acts very well in practice, & the "triangle" is, of course, very
portable; it has all the advantages, before mentioned, of Class I, except that it is
unsuitable for finding the distance of a rapidly moving object.

page_text: 10. The arrangements for graduation, to enable the observer to read off the
ranges, are these:-
In the method No. 4.-the "four-bar-linkage" plan (Figs. 6. 7. 10.)-the
graduations are marked on a rule B T shown as pivoted at B and so guided as to
be parallel to the line M M' joining the mid points of A a and Dd, and thus
parallel also to the line A D B' of Fig. 1. The graduations on this rule are cut
by a thin wire, Dz, Fig. 6, fixed at its end D, and joined at its other end z by a
small elastic spring, or thread, to a point 2 on b d produced backwards through d
so that length bz is equal to D B. The length of BT as cut by this wire will
then always be equal to the length mentioned in formula II (par. 1). There are
various pins at z to suit the different lengths of D B when enlarged or decreased,
(par. 6.) to decrease or enlarge the supposed base-line D C.
In the other methods described in pars. 3. 4. & 5. the sight-line B6 has a light
index, which can be drawn out so as to cut a graduated rule D B' (Fig. 1.) which
is set by being pointed to A..
In the method No. 4. the graduated rule B T is over three feet in length, and
folds on D d for portability. Its graduations are wide & distinct. The rule has
three or more lines of graduations on it to suit different lengths of the "base "DC;
the mathematical reason for this advantage is becanse the length (formula II) for
"base-line"
"base-
a range R, and a
T, is the same as for a range of half R with a
line of half r,
& so in any other proportion. This in fact multiplies the length of
the graduated rule by as many "base-lines" as may be selected for use.
11. Among the advantages of this invention are the following:-
"
1. Great speed in distance-finding.
2. Absence of base-measurements on the ground, or of the need of setting out
right angles or any angles.
3. Small amount of drill required to teach the use of the instrument: young
lads have learned it after seeing a few ranges found.
4. The imaginary line DC (or r), which acts as a base, can be made of any
length, at once, by merely turning a screw in the instrument.
5. Consequent minimum exposure of the observer when the instrument is used for
inilitary range-finding.
6. Consequent latitude of choice of ground for distance-finding, any line of 5 to
10 yards being sufficient whether under cover or not.
7. No calculation of any kind required, the process being the same for a long as
for a short range.
8. In the portable forms of the instrument, the tripod stands, being once pitched
on the ground, can be used, without shifting, for taking the distances of any
number of objects in view.
9. The instrument can take the distances of moving objects as well as of those
that are stationary.
10. It can also readily find the distance of a remote light, at night, whether
moving or stationary.
11. It also readily finds the mutual distances of remote objects.
12. The graduations for reading off the distances are on a large scale, wide &
distinct on a rule of length three feet or more, itself multiplied also by the number
of lines of graduation on it (par. 10).
13. Absolute simplicity of construction, especially of the form called the "four-
bar-linkage" (par. 6).
14. Consequent absence of parts likely to get out of order, & cheapness of
construction, and easiness of repair.
15. Portability of the instrument, which can be carried by a man on foot, or as
a lance is carried on horseback.
12. Having now particularly described & ascertained the nature of my said inven-
5 tion, and in what manner the same is to be performed, I declare that what I claim is :-
First. The determination of a movable sight-line, or telescope axis (Bb,) to

page_text: pass always, whatever be its movement, through a point (C,) fixed in space in the
supposed prolongation of a line (D d,) drawn on a bar set in position by the
observer, and at any desired distance in front of that bar,-by any one, or all, of
the following alternative methods, or arrangements attached to that bar, substan-
tially as specified, viz.,―
(a.) By attaching this sight-line, or telescope, perpendicularly to a collar
sliding along an arc of a circle of radius equal the required distance:
(b.) By a linkage similar to that known as Peaucellier's linkage for drawing
a straight line," but differing therefrom and having sundry new additions
thereto :
(c.) By the unequal revolutions of two spindles having equal screw threads,
or the equal revolution of two spindles having unequal screw threads
differing in a fixed ratio:
(d.) By a linkage called the "four-bar-linkage," consisting of four bars, or
links arranged as a parallelogram with two opposite sides produced.
Second. The combination of the foregoing with a second & parallel bar (A a),
carrying sighting instrumentalities, so as together to constitute an instrument
suitable for rapidly measuring long distances in survey work, or range-finding for
military purposes, the parallelism between the two bars (A a, and Dd,) being
determined by any one, or all, of the following alternative methods, substantially
as specified, viz.―
(a.) For instruments used in fixed positions, or on board Ship:-By two equal
parallel rods, furnished with light cross rods, & connected at their ends by
pivots with points on the said bars, making with them a parallelogram, the
whole mounted on a small platform, which has a slight central rocking
movement round its central line:
(b.) For portable instruments :-By making those parallel rods in sections
with mutually fitting ends, or using two parallel sets of " lazy-tongs" with
light cross rods pivoted at their nodes or centres :
(c.) For portable instruments :-By a combination of four bars, into a
parallelogram, called the "adjusting-four-bar-linkage," having two sight-
bars (Mn and DP):
(d.) For portable instruments :-By a "movable triangle," one side of which
is a sight-bar (Sn), & another a rod (RS) capable of being clamped at any
point of its own length to that sight-bar.
Third. The method of graduating and using that part (BT) of the instrument
in the "four-bar-linkage "form, used as a graduated scale to show the distances
found.
Dated this hiftoonth do
J
1004
WEBB GILLMAN,
Lieut. R.H.A.,
Of Clonteadmore, Coachford, Co. Cork, now stationed at Meerut, in India.