improvements in Range Finders.
Year: 1893

page_text: Date of Application, 12th July, 1893
Complete Specification Left, 15th May, 1894-Accepted, 12th July, 1894
improvements in Range Finders.
We, ARCHIBALD BARR, Professor of Engineering in the University of Glasgow,
and WILLIAM STROUD, Professor of Physics, The Yorkshire College, Leeds, do
hereby declare the nature of this invention to be.as follows
The object of our invention is to provide more efficient means for determining
ranges.
The improvements relate to the class of single observer range finders or telemeters,
and are specially applicable to telemeters of the kind described in the Specification
of our prior Patent No. 9520, A.D. 1888, though in some cases they are applicable
to other forms of single observer instrument.
Our principal improvements are-
1st. The substitution of a metal frame-piece (preferably copper) of special con-
struction for the tube customarily used for supporting the optical parts of such
instruments. This frame-piece may be of cast metal, but, especially for large
instruments, we prefer to construct it of two bars of copper or other suitable
material lying one above the other and connected together by bracing in a form
somewhat analogous to the bracing of a framed girder. The bracing may be
constructed of distance pieces and wire ties or of a strip of metal bent backwards
and forwards in a zig-zag form and pierced with suitable apertures for the passage
of the beams of light.
2nd. Improved arrangement of prisms or reflectors placed at the centre of the
instrument for receiving the beams of light and reflecting them to the eye of the
observer. A prism is placed with one edge parallel to the length of the instrument
and in the focus of the eye-piece in such a manner that the image formed by light
coming from, one end of the instrument is situated above this edge, and the other
image below the edge, the edge forming the line of separation between the two
images. We may sometimes construct this prism of speculum metal or other opaque
reflecting material, in which case the surfaces above and below the edge recede
from the eye-piece, and receive light reflected downwards and upwards respectively
from other reflectors placed above and below the prism.
In other cases this prism may be made of glass with the separating edge remote
from the eye-piece and reflecting the light either by total reflection (say by an
equilateral prism) or by silvered surfaces according to the angle at which the prism
is designed to receive the rays. In other cases still we may use a prism of glass of
square or rhomboidal section (or approximately so) through which the light is
transmitted and refracted, the near edge of the prism forming the separating edge
referred to. In the last of the alternatives referred to a single reflector suffices for
each beam to direct it towards the separating edge. In each of the other cases two
reflecting surfaces are necessary in each of the beams to direct the light on to the
separating edge.
3rd. Improved means of accomplishing the adjustment,
Specification we have called the adjustment for "halving."
plish by moving the separating prism above referred to
eye-piece.
which in our previous
This we may accom-
towards or from the
4th. With a view to determining the ranges of lights at night, or the ranges of
other objects difficult to observe upon on account of their small apparent dimensions
or irregularity of outline, we may place in one or both of the beams of light one
or more lenses having cylindrical surfaces so arranged as to astigmatise one or

page_text: both images, giving it or them the appearance of one or more lines or streaks
perpendicular to the length of the instrument.
5th. With a view to recognising the position of the separating edge in the field of
view at night, we may provide means for very slightly illuminating one section of
the field of view. This we may accomplish by placing in front of one of the
objectives a small reflector so arranged that the light of an electric lamp (say one
used also for illuminating the scale) is reflected along one of the beams, or by other
somewhat analogous means.
6th. With a view to closing the outer case so as to exclude rain or dust or
currents of air, we may provide windows made of glass having flat faces parallel or
nearly so to each other and attached to the outer case of the instrument.
7th. The outer case of the instrument may be made of two tubes, one outside the
other, connected together at all their apertures so as to enclose a space between
them, which space may be filled with water or other liquid, or left simply filled with
air, so that the enclosed fluid may by its non-conductivity and by its convection
minimise the passage of heat to or from the instrument, and tend to equalise the
temperature of the two sides of the tube or frame-piece supporting the optical
parts.
8th. When the instrument is to be used on board ship we may provide a specially
constructed stand upon which the instrument is supported in such a manner that it
is capable of being rotated in azimuth, and, when desirable, in altitude, and further
the instrument may be supported from the stand by means of bearings or knife-
edges so placed that the centre of gravity of the instrument and attached parts
shall be below the point of support and thus tend to maintain a constant direction
in altitude independently of the motions of the ship. A portion of the stand may
be made in the form of a vessel to contain water or other liquid in which a counter-
poise or other piece attached to the instrument may be submerged, and thus the
oscillations of the instrument may be damped.
Dated this 11th day of July 1893.
BOTTOMLEY & LIDDLE,
154, St. Vincent Street, Glasgow, Applicants' Agents.
We, ARCHIBALD BARR, Professor of Engineering in the University of Glasgow,
and WILLIAM STROUD, Professor of Physics, The Yorkshire College, Leeds, 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 our invention is to provide more efficient means for determining the
ranges or distances of objects.
The improvements relate to the class of single observer range finders or telemeters,
and are specially applicable to telemeters of the kind described in the Specification
of our previous Patent No. 9520, A.D. 1888, though they are applicable to other
1orms of single observer instruments.
Our principal improvements are
1st. The substitution of a metal framepiece, (preferably copper) of special
construction for the tube customarily used for supporting the optical parts of such
instruments. This framepiece may be of cast metal, but, especially for large
instruments, we prefer to construct it of two bars of copper or other suitable
material lying one above the other and connected together by bracing in a form
somewhat analogous to the bracing of a framed girder. The bracing may be
constructed of distance pieces and wire ties, or of a strip of metal bent backwards

page_text: and forwards in a zig-zag form, and pierced with suitable apertures for the passage
of the beams of light.
2nd. Improved arrangement of prisms or reflectors placed at the centre of the
instrument for receiving the beams of light and reflecting them to the eye of the
observer. A prism is placed with one edge parallel to the length of the instrument
and in the focus of the eye piece in such a manner that the image formed by light
coming from one end of the instrument is situated above this edge, and the other
image below the edge; the edge forming the line of separation between the two
images. We may sometimes construct this prism of speculum metal or other
opaque reflecting material, in which case the surfaces above and below the edge
recede from the eyepiece and receive light reflected downwards and upwards
respectively from other reflectors placed above and below the prism.
In other cases this prism may be made of glass with the separating edge remote
from the eyepiece and reflecting the light either by total reflection (say by an
equilateral prism) or by silvered surfaces according to the angle at which the
prism is designed to receive the rays. In other cases still we may use a prism of
glass of square or rhomboidal section (or approximately so) through which the
light is transmitted and refracted, the near edge of the prism forming the separating
edge referred to. In the last of the alternatives referred to, a single reflector
suffices for each beam to direct it towards the separating edge. In each of the
other cases two reflecting surfaces are necessary in each of the beams to direct the
light on to the separating edge.
3rd. Improved means of accomplishing the adjustment, which in our previous
Specification we have called the adjustment for "halving." This
we may
accomplish by moving the separating prism above referred to towards or from the
eyepiece.
4th. With a view to determining the ranges of lights at night, or the ranges of
other objects difficult to observe upon on account of their small apparent dimensions
or irregularity of outline, we may place in one or both of the beams of light one or
more lenses having cylindrical surfaces so arranged as to astigmatise one or both
images, giving it or them the appearance of one or more lines or streaks
perpendicular to the length of the instrument.
5th. With a view to recognising the position of the separating edge in the field
of view at night, we may provide means for very slightly illuminating one section
of the field of view. This we may accomplish by placing in front of one of
the objectives a small reflector so arranged that the light of an electric lamp (say
one used also for illuminating the scale) is reflected along one of the beams, or by
other somewhat analogous means.
6th. With a view to closing the outer case so as to exclude rain or dust or
currents of air, we may provide windows made of glass having flat faces parallel or
nearly so to each other and attached to the outer case of the instrument.
7th. The outer case of the instrument may be made of two tubes, one outside the
other, connected together at all their apertures so as to enclose a space between
them, which space may be filled with water or other liquid or left simply filled with
air, so that the enclosed fluid may by its non-conductivity and by its convection
minimise the passage of heat to or from the instrument, and tend to equalise
the temperature of the two sides of the tube or framepiece supporting the optical
parts.
8th. When the instrument is to be used on board ship we may provide a specially
constructed stand upon which the instrument is supported in such a manner that it
is capable of being rotated in azimuth, and, when desirable, in altitude; and
further, the instrument may be supported from the stand by means of bearings or
knife-edges so placed that the centre of gravity of the instrument and attached
parts shall be below the point of support and thus tend to maintain a constant
direction in altitude independently of the motions of the ship. A portion of the
stand may be made in the form of a vessel to contain water or other liquid in which

page_text: a counterpoise or other piece attached to the instrument may be submerged, and
thus the oscillations of the instrument may be damped.
In order that the nature of our improvements in range finders and the manner in
which the same may be performed may be more clearly and fully understood we
will now describe them with reference to the accompanying drawings and to the
letters and marks thereon. In the various figures the same letters are used to
indicate the same or like parts where they occur.
Figures 1 and 2 show a range finder constructed in accordance with our Patent
No. 9520, A.D. 1888, and embodying some of the improvements to which this
Specification more especially refers.
We do not propose to state herein the general mode in which the instrument is
to be used, since that has already been fully described in our previous Specification.
We describe herein the nature of our improvements and the manner in which these
may be carried into effect. For the sake of clearness in the following description,
we shall assume that the instrument is placed with its length horizontal and that
it is directed to view an object at or near the level of the horizon.
A is the outer case of the instrument composed of two tubes in the manner above
referred to, the mode of constructing which will be evident from Figures 1, 2
and 3. When it is desired to use water or other liquid between the two tubes the
connections at the various apertures should be made watertight, and a screwed plug
or other arrangement for the introduction of the liquid may be provided.
B', B is the framework carrying the principal optical parts of the instrument,
especially the reflectors C1, C2 which are represented as being made of speculum
metal, the object glasses contained in holders D', D2 and the eye-piece prisms
described below, contained in a box E.
This framework B', B2 consists of two metal bars, preferably of copper, on
account of its high conductivity for heat, of the section shown in Figure 3, or
other suitable section, connected together by a system of bracing. This bracing F
may consist of wires or rods, but we prefer to construct it of a strip or plate of
copper or other metal, F, (preferably with thickened edges) which is bent upwards
and downwards as shown in Figure 1, and soldered or riveted or otherwise attached
to the bars B1, B2. This strip F is pierced with apertures of the necessary
dimensions to allow the passage of the beams of light (reflected respectively
from C1, C2) to the eye-piece prisms. This bracing therefore constitutes a system.
of diaphragms, besides giving strength to the frame. We may sometimes use a
cast-metal frame of a construction somewhat similar to that above described.
The essential feature of this framework is that the upper and lower bars being flat
or nearly flat expose much less surface than a tube would do to receive heat from
the front or back of the instrument, and in the second place afford the best means
for the conduction of the heat received from the back to the front of the frame-
work, or vice versa, thus tending to maintain the front and back portions of the
frame or support carrying the optical parts of the instrument, or some of them, as
nearly as possible at the same temperature. It is not essential that the upper and
lower bars should be so nearly at one and the same temperature. The framework
described has then the advantages over the tube hitherto customarily used for
supporting the optical parts, or some of them, of single observer range finders or
telemeters, that it affords convenient access to the various parts during constructio
and subsequently, and that it greatly lessens the liability of the instrument to give
erroneous indications due to bending caused by unequal heating at the front and
back of the instrument.
The framework supported from the outer case A of the instrument by means
of two bearing rings or pieces G', G2, one of which G' is (as shown in the
drawings) constructed in a similar manner to the gimbal ring of a mariner's
compass. The other bearing ring G2 we prefer to construct as illustrated in
Figure 3. The ring G2, which is fixed to the outer case by screws or other means,
carries three screwed plugs H', H2, H3 containing conical or spherical recesses at

page_text: their inner ends, and the instrument is supported by means of three pillars or
struts 11, 12, 13 extending between these conical or spherical recesses and similar
recesses in parts attached to the framework B', B².
J¹, J2, Figure 2, are windows, preferably constructed of optically parallel plane
glass, which serve to exclude rain and dust from the interior of the instrument.
K is the frame carrying the deflecting prism; L the screw operating that frame.
M is the scale; N' the right eye-piece; N the left eye-piece, all substantially as
described in our previous Specification.except in so far as modified in accordance
with improvements herein described.
**
to
O is a small object glass, which together with a concave lens in the eye-piece N
constitutes a small Galilean telescope which we sometimes use as a finder
enable the observer more quickly to direct the instrument upon any given object,
in the same manner as the "finder" facilitates the use of an astronomical telescope.
In this case the concave lens N2 above referred to may only occupy one half of the
aperture of the eye-piece, the other half having opposite to it a portion of a convex
lens by means of which a portion of the scale, and an index attached to the frame-
work B1 B2 may be seen. The scale is preferably in this case kept above or below
the level of the centre of the instrument so as not to interfere with the view of the
object to be observed through the finder. Instead of the milled head attached
directly to the screw by which the deflecting prism is operated as described in our
previous Specification above referred to, we sometimes substitute a pinion P, into
which a wheel Q gears, the wheel Q being mounted upon the spindle of a toothed
roller R which is operated by the fingers of the observer. The axle of the
pinion P is supported in bearings attached to the outer tube A, and the screw L is
supported in bearings attached to the framework B' B². A link connecting the
axle of the pinion P with the screw L is provided with couplings t¹, t² so
constructed that while they communicate rotary motion from the axle they impart
no important forces tending to bend the framework. The construction of such
couplings is described below with reference to the "halving adjustment."
In Figures 4, 4, 5, 5ª, 6, 6, 7, 7, 8, 8, 9, 94, 10, 10 we show several methods
of carrying out our improved system of constructing the optical arrangements
situated in the centre of the instrument for reflecting the beams of light to the eye
of the observer, but it is to be understood that we do not confine ourselves to these
arrangements, as there are other modifications possible retaining the separating
prism, which is the chief characteristic or feature of our improved system; and
further plane mirrors may in some cases be substituted for reflecting prisms where
such mirrors would produce a like effect. These optical arrangements, (which in
the instrument are contained or held in a case or holder E, shown in Figures 1
and 2, and in more detail in Figures 11, 12, and 13) we usually designate "eye-
piece prisms.' Figures 4, 4 show one arrangement of such eye-piece prisms.
T is a prism of speculum metal or other opaque reflecting material, with an edge S as
sharp as possible, which edge is situated in the focus of a lens or eye-piece N¹.
This prism or its equivalent in other arrangements we designate the " separating
prism."U1, U2 are two pieces of glass, each of which may be formed of two prisms
cemented together, or of one piece having the form of such. a combination. For
convenience we shall call these reflectors "prisms even when compound.
"
"
These
prisms U U receive upon their faces V1 V2 beams of light from the two ends of
the instrument respectively and reflect these beams through a right angle or
approximately so, on to the sloping faces WW2, whence they are reflected
through the faces X'X' on to the "separating prism" T which again reflects them
through the lens or eye-piece N'. The several angles of these prisms may be
somewhat modified, but we prefer to make the angle at S of the "separating
prism" 90°, and the angles between the faces W'X', W2X2 45°.
Figures 5, 5 show an alternative arrangement in which the speculum metal
separating prism is replaced by a totally reflecting prism (or combination of two
prisms TT2).

page_text: The prism T¹ is cemented to the prism T2 by means of Canada balsam or other
transparent material of as nearly as possible the same refractive index as glass.
Figures 6 and 64 show another alternative arrangement in which the separating
prism is equilateral or nearly so; in this case the faces W1 W2 are parallel
respectively to the remote faces of the separating prism" T, while the
faces X'X' are parallel or nearly so to the near faces of the ";
'separating
prism" T.
66
Figures 7, 7 show another alternative arrangement. U¹ U represent right-
angled prisms arranged to receive the beams of light from the objective and to
reflect them away from the eye-piece into the prism T. The faces W₁ X' of the
prism T are at right angles to each other (and the faces W2 X² are at right angles
to each other) while the angle between the faces X1 X2 is preferably a few degrees
greater than 120°,-say 125°, in order to allow rays of light passing from the
reflecting face W2 to points on the reflecting face X2 (close to the edge S) to pass
clear of the face X'. The paths of two rays are shown in the drawing. In this
case the faces X and X2 must be silvered.
"
In another arrangement shown in Figures 88* the "separating prism T is of
speculum metal or other opaque reflecting material. The prisms U¹ U' receive the
beams of light on their faces V1 V2 and reflect them away from the eye-piece to
the faces WW2, which reflect them to the separating prism T whence they are
reflected to the eye-piece.
The arrangement shown in Figures 7 and 8 have the advantage that the object
observed is caused to appear erect without the aid of an erecting system of lenses
in the eye-piece.
In all the above cases it will be noted that there are three reflectors for each
beam in the "eye-piece prism" combination, two reflecting surfaces being necessary
in each of the beams to direct the light on to the separating edge. In the next
case however, Figures 9, 94 two of the reflections are replaced by two refractions.
T represents a prism of glass whose section is a square or a rhomboid (or
approximately so) through which the beams of light (after reflection from the
prisms U¹ U2) are transmitted and refracted as shown. In this case the edge of
the prism nearest the eye-piece forms the separating edge, and upon it the eye-piece
is focussed.
Figures 10, 104 show another arrangement of prisms in which the light is
refracted in passing through the inclined faces X1 X2 of the prisms U₁ U2. In
this case the prisms U₁ U2 may be made of crown glass, and prisms Z' Z² of
flint glass may be cemented to those faces in order to constitute an achromatic
arrangement. The images are, as in the other cases, formed above and below the
separating edge S of the separating prism T, the faces of which have such an
angle that the beams of light striking them in an inclined direction are caused to
become parallel to one another before passing through the eye-piece.
In the eye-piece prism arrangements shown in Figures 5, 5, 6, 64, 7, 74, 10, 104,
the field lens of the eye-piece (or a single lens eye-piece-if such be used) may be
cemented on to the outer surface of the separating prisms as shown. Or the outer
face may, in some cases, be ground convex so as to be equivalent thereto.
It is to he understood that the essential feature of our improved system of
eye-piece prisms is the use of a prism, (which for distinction we call the separating
prisin) having one edge (which for distinction we call the separating edge) parallel
to the length of the instrument and in the focus of the eye-piece (or nearly so)
which prism is so formed and disposed that the two images formed by light entering
at the two ends of the instrument respectively are formed at or near the edge
referred to, and while the rays forming the images approach the separating edge
in different directions they are respectively either refracted at, or reflected by the
two faces which meet in the separating edge so as to pass through the eye-piece
as if they came from one image. The portion of one image which falls below the
separating edge, and the portion of the other image which falls above that edge
are not seen by the observer.

page_text: Figures 11, 12, and 13 show our improved method of effecting the "halving-
adjustment"; Figure 11 being a side view of the arrangement as seen from the
right hand end of the instrument; Figure 12 an elevation looking toward the
observer, and Figure 13 a horizontal section.
The arrangement of eye-piece prisms shown in these figures is that shown in-
Figures 6, 6, but the method is applicable also to other systems of eye-piece
prisms constructed upon our improved method, as for example those shown in
Figures 4, 5, 8, 10. The prisms U¹ U² are held in a box m fixed to the frame--
work B1 B2, while the separating prism T is held in a metal piece n, to which are-
attached two plates O which pass along the sides of the box m. These plates are
connected at the end remote from n by means of a piece P. Another piece Qis-
fixed across the back of the box m, and springs R, tend to force P and Q apart
while they are pulled together by means of a screw a actuated by a worm wheel b.
driven by a worm c, so that when the worm is rotated the piece P is moved
backwards or forwards, carrying with it the cheeks or plates O and the block n;
and thus the separating prism T is moved outwards or inwards relatively to the
prisms U U The effect of such motion (as will be obvious from the paths of
the reflected rays as shown in Figure 6) is to cause the two partial images of the
objects observed, seen respectively above and below the separating edge S, to
appear to move vertically towards or from each other, by which means the-
adjustment which we term "halving" is accomplished.
Apertures as shown at d are made in the sides of the box m and in the cheeks O,
so as to admit the beam of light from the two ends of the instrument to the
prisms U U respectively.
The shaft e, Figures 12 and 13 is connected to a milled head f, Figures 1 and 2,
by means of a shaft g, Figures 1 and 2, preferably provided with couplings ¹²
so constructed that while they communicate rotary motion from the shaft carrying
the milled head they impart no important forces to the framework B2 tending to
bend the latter. Such couplings may conveniently be constructed as follows..
Short pieces of cylindrical tubes having two longitudinal slots diametrically
opposite each other are fixed on the ends of the shaft g. The shaft e and the.
spindle carrying the milled head f have each a spherical or somewhat spherical
end which ends lie within the tubes referred to, and pins passing through these
spherical ends engage in the slots of the tubes attached to g and communicate.
rotational motion to the latter while exerting no important longitudinal or bending
stresses.
The coincidence adjustment may be effected in one or other of the manners
described in our previous Patent above referred to. In Figures 1 and 2 the
scale M is shown attached to a screw i which passes through a nut j carried upon
the prism-frame K, but free to revolve relatively thereto. By turning the nut.
the relative position of the scale and the prism is altered and thus the instrument
can be adjusted so that when the partial images of any object are seen in correct
coincidence the scale shall read the true distance. Access to the nut may be..
obtained through an aperture in the case A provided with a removable cover.
Figures 14 and 15 show one means of carrying out our improved method for
the observation of lights and other objects difficult to observe upon on account of:
their smallness of apparent dimensions or irregularity of outline.
k₁k₂ are lenses or pieces of glass having one or both surfaces ground to either a
concave or convex cylindrical form, such as the lenses used by opticians in spectacles-
to neutralise "astigmatism," but we use lenses of greater curvature than ordinary
spectacle lenses when we introduce them in the position indicated in the drawings..
These lenses are fixed to a rocking-lever which is pivoted upon the outer end
of the screw a shown in Figure 11. The lever is kept in its position by means of
a collar or other suitable device.
This lever is omitted in Figures 1, 2, 11, 12, 13 to avoid confusion.
When the lever is in the position represented in Figures 14 and 15 the beams of#

page_text: light coming to the prisms U¹ U' from the two ends of the instrument respectively,
pass through these "astigmatising " lenses.
The effect of interposing these lenses is to cause the images of a spot of light
to appear as a line at right angles or approximately so to the separating edge S
before mentioned.
1
When not required the lenses may be removed from the beams of light by
rotating the lever / so as to bring the lenses k₁ k₂ into the positions indicated by the
dotted lines at k¹, k¹₂. The lever is operated from the outside of the tube A. by
means of crank q, the pin p of which passes through a slot t in the lever in such
a manner as not to apply forces tending to bend the framework B' B2 of the
instrument.
The crank g is worked by means of a lever lying outside of the tube A, as
shown in Figures 15, 16 and 19, the crank q and the lever » being fixed to a spindle
passing through a suitable bearing carried by the tube A.
The screw u, Figure 15, is for the purpose of stopping the lever l, and consequently
the lenses k₁k, in the desired position.
We do not confine ourselves to this mechanism for putting the cylindrical lenses
into the paths of the beams or removing them from the paths of the beams; nor
do we confine ourselves to introducing the lenses in the position indicated in the
drawings.
Lenses having one or both surfaces cylindrical may be introduced into the beams
of light at any point of the course of those beams. Thus they may even be
introduced outside of the windows so that the beams pass through them before
entering the instrument, the lenses being chosen of such a curvature as to produce
the desired length of streak.
One lens may be introduced into the two beams of light after these have passed
the separating edge and either before or after the beams have passed through the
eye-piece or one lens of the eye-piece, but this has the disadvantage that the
separating edge will no longer be clearly visible while the object is astigmatised.
In Figures 1, 2, and 3 the outer case A is shown constructed of two tubes, one
outside of the other in accordance with our improved system above described.
One or both of these tubes is preferably constructed of a metal having high
conductivity for heat, such as copper, in order to further equalise the temperature
around the framepiece or tube to which the optical parts are attached.
Figures 16, 17, 18, and 19 show our improved arrangement of stand for the
instrument, suitable for use on board ship. "H" represents a pillar or pedestal
constructed of wood or metal carrying a vertical spike or pivot G. This pillar H"
is fixed to the deck or other portion of the ship by suitable screws or other
connections. A tank F is supported upon the spike G" so as to be free to revolve
in azimuth about the latter. This tank may conveniently be constructed of three
cast metal plates of the shape shown in outline in Figure 17, which form its two
ends and a central diaphragm. A sheet of metal is bent round these plates and
fastened to them, thus forming the front, bottom and back of the tank. The
central diaphragm may contain a socket to fit over the spike G", and the tank may
have a flange or facing 11 resting upon a corresponding facing J" attached to the
pedestal H. Knife-edges E" fixed to the ends of the tank support a frame-
work C to which a balance weight D" is attached; this framework C also
supports two forks or bearings B₁₁B", In these bearings B" B", the instru-
ment A rests so as to be free to be turned about its longitudinal axis, while it may
be prevented from moving endwise by means of slightly projecting flanges or
collars attached to the instrument and lying on each side of one of the bearings.
The instrument A may be secured in the bearings B₁₁ B", by means of
hinged cover pieces K", K", fixed to the bearings by means of pins. Attached to
the swinging frame a handle L", Figures 16, 17, 18, may be provided; most
conveniently placed at the left hand side of the observer when using the
instrument.

page_text: The tank may when desirable be partially filled with water or other liquid as
shown in Figure 18.
During use the instrument may be turned in azimuth about the spike G", and
may be rotated in the bearings B", B", to the required angular altitude, but the
latter motion may also be accomplished by swinging it upon the knife-edges E" by
aid of the handle L". Again if the instrument is set by rotation in its bearings so
as to be directed toward the horizon or other altitude the balance weight D¹¹ tends
more or less to maintain the direction of observation independently of the rolling
or pitching of the ship, while the tendency of the instrument to oscillate may be
checked or damped by means of liquid in the tank, and the observer may further
control such motions by use of the handle. The tank further serves, though no
water be used in it, to shield the balance weight from the wind which otherwise
would tend to move the instrument in altitude.
1
Bearings of the ordinary form, or ball or roller bearings may be substituted
for the knife-edges E"; or again bearings equivalent to B, B", may be attached
to the tank or an equivalent supporting framework free to revolve in azimuth
relatively to the pillar H", and the instrument A may be supported in such
bearings and have attached to it a balance weight equivalent to the balance
weight D. In this case the bandle L" would be attached to the instrument A.
Having now particularly described and ascertained the nature of our said
improvements in range finders or telemeters and in what manner the same are to
be performed, we declare that what we claim is :-
1. The use in single observer range finders or telemeters of a metal frame-
work consisting essentially of two flat or nearly flat pieces connected together by
bracing, for supporting the optical parts of the instrument, such framework being
either cast in one or more pieces or built up of strips or rods of metal, substantially
as described.
2. In single observer range finders or telemeters, the use of a prism having one
edge situated in the focus of the eye-piece or nearly so and parallel to the length
of the instrument, which prism is so arranged in combination with other prisms or
reflectors that the partial images of an object viewed through the instrument are
formed respectively above and below this edge, while the beams forming these
images are respectively reflected by or refracted at the faces of the prism which
meet in the edge referred to, substantially as and for the purpose herein described.
3. The use of a lens or lenses interposed into one or both of the beams of
light by which an object is seen, for the purpose of drawing out or
'astigmatising one or both of the images, substantially as and for the purpose
herein described.
66
"
4. The use of an outer case composed of two tubes connected together at their
apertures and enclosing water, air, or other fluid, for the purpose of retarding and
rendering more uniform the communication of heat to and from the tube or frame-
piece supporting the optical parts of the instrument.
5. A stand for supporting single observer range finders or telemeters on board
ship, substantially as described with reference to Figures 17, 18 and 19.
6. In a stand for supporting single observer telemeters on board ship, the
construction of a portion of the stand in the form of a box or tank which may
be partly filled with water, or other liquid, in which a balance weight or other
piece attached to the instrument may be immersed so that the oscillations of the
instrument in altitude may be checked or damped.
Dated this 12th day of May 1894.
BOTTOMLEY & LIDDLE,
154, St. Vincent Street, Glasgow, Applicants' Agents.