Improvements in Instruments for Measuring Distances and Angles, Specially Applicable to Telemeters or Range Finders and other Analogous Instruments.
Year: 1888

page_text: Date of Application, 30th June, 1888
Complete Specification Left, 30th Apr., 1889-Accepted, 29th June, 1889
PROVISIONAL SPECIFICATION.
Improvements in Instruments for Measuring Distances and Angles,
Specially Applicable to Telemeters or Range Finders and other
Analogous Instruments.
We ARCHIBALD BARK professor of Engineering and WILLIAM STROUD professor of
Physics both of the Yorkshire College Leeds in the County of York do hereby declare
the nature of this invention to be as follows:-
The object of our Invention is to provide an instrument whereby the distance of
moving or stationary objects or the size of the same may be easily and rapidly
indicated or ascertained, with a considerable degree of accuracy; whilst the base line
from which such observation or observations are made may be of very limited length :
such instrument being also capable of measuring or indicating with like facility and
accuracy the angle included by lines of direction, which have but an exceedingly slight
inclination with regard to each other; and also the direction and the rate of the motion
of moving bodies.
Our Invention further relates to the means for mounting such instrument for the
special purpose for or to which it may be applied, and for avoiding any liability to
derangement or damage during use or transport:-to means for correctly adjusting
the same either during construction or for the correction of any derangement it may
have suffered during use or transport:-and lastly to the combination with it of means
for levelling or contouring, and ascertaining the dip and azimuth of objects observed by
the instrument.
Our principal improvements are specially applicable to Range Finders for Military
and Surveying purposes, and are hereunder described chiefly with reference to the
former; but it will be evident that they can he readily applied for other purposes,
where it is requisite to measure distances or angles.
An instrument constructed in accordance with our Invention, consists of a pair of
mirrors or reflecting prisms, placed at or near the ends of a tube (or frame piece);
the optical length of which forms, so to say, the base of the triangulation or observation
usel for ascertaining the distance of the object observed. Near to each of these outer
mirrors (or prisms) either in or about the line joining the same, or in the lines of
sight from the object to the outer mirrors (or prisms) respectively, is placed an object
glass or lens. Between the mirrors (or prisms), preferably midway and in or about
the line joining the same are provided two small reflecting mirrors (or prisms), placed
the one above the other, and facing the one, one of the outer mirrors (or prisms) and
the other the other outer mirror (or prism). A small eye-piece is placed in front of
these two centre reflecting mirrors (or prisms) to receive and magnify the images. In
the path of the rays between one of the object glasses, and the corresponding reflecting
centre mirror or prism. is introduced a deflecting prism, generally of very small
angle; which is moveable longitudinally along the path of the rays traversing it from
the outer to the inner mirror (or prism). This deflecting prism is placed or mounted
on or in a guide or slide; and connected with the prism, or the mechanism by which
it is moved, is a scale for the purpose of indicating the distance of the object being
observed, or the angle being measured.
The rays of light from the distant object are received first by the outer reflecting
mirrors (or prisms) and object glasses at the two ends of the instrument, and are
reflected inwards and towards the centre reflecting mirrors (or prisms); which latter
are so placed as to receive the corresponding rays and to reflect them to the eye-
piece.
This arrangement just described is such, that an object viewed is partly seen by
reflection from one of the centre mirrors (or prisms), and partly by reflection from

page_text: the other of the same. It will be evident that by moving the above referred to
deflecting prism, the image of the portion of the object seen by the rays traversing it
from the corresponding end of the instrument, is moved relatively to the image of "the
other part seen by the rays coming from the opposite end of the instrument. The
instrument is so njusted, that when the deflecting prism is in a certain position, and
the rays entering the two ends of the instrument are practically parallel, the images
of the two portions of the object viewed appear in correct juxtaposition, and the scale
by which the distances are read may be so marked as to indicate an infinite distance.
When however the rays entering the two ends of the instrument make any other
angle with each other, as for example when un object at a distance of say 1000 yards
is viewed, the images will not be in correct juxtaposition if the deflecting prism is in
the given position above referred to; but the images may be adjusted to become so,
by moving the deflecting prism io a certain extent and the scale may be marked, so
that in its new position, it indicates the distance of the object (riz. 1000 yards).
When in the first example the instrument as arranged for measuring angles is
employed, the lines or rays being parallel, the scale may be marked to indicate zero.
In the second example, if the length of the instrument, or more correctly the optical
Inse is say 2 feet, the scale may be marked to indicate an angle whose sine is souths
i.e. about 2 min. 17 sec.
3000
If the instrument he mounted so as to be capable of rotation about both a vertical
and an horizontal axis, and be provided with means for accurately adjusting these
axes truly vertical and horizontal; and also with properly graduateul arcs or circles
attached to these axes; the azimuth and declination or dip (or rise) of the object
observed can then also be readily ascertained and the instrument also will be capable
of being employed for surveying and contouring, for ascertaining the direction of and
the rate of the motion of a moving body, or the distance apart of moving or fixed
bodies (as ships at sea, forts etc.) and the size of distant objects.
Without such mountings and additions moreover, will be possible to ascertain
the rate of motion of a body moving in a direct line towards or from the observer, by
ascertaining the distances of the moving body at the beginning and end of a measuredl
interval of time.
In order to avoid or lessen any liability to derangement or damage during use or
transport, wo propose to enclose the instrument in an outer tube or case, within which
it is held by elastic or flexible connections (gimbal rings for example) so that the
instrument may be protected from distortion by pressure on or unequal expansion of
parts of the outer case, when held in the hands of the observer, or dua to other out-
side forces or conditions, which are thus prevented from rendering inaccurate the
readings or indications of the instrument.
For a like purpose the eye-piece (or -pieces, where n second is employed for
reading the indications on the scale), and portions of the mechanism for moving the
deflecting prism may be attached to the outer case. The scale on which the readings
or indications are marked, may be conveniently placed inside the tube or other case
of the instrument; and arrangements made for illuminating it directly, or by trans-
mission, and an eye-piece or lens provided for more readily and accurately reading
the marks on the same.
The deflecting prism attached to a sliding piece may be moved directly by hand, or
by means of rack and pinion or screw or other mechanism.
The instrument may he hold merely by the hand, or we provide special means for
attaching it to rifles, or guns, or convenient forms of stands or supports.
Our improvements for adjusting the instrument when first constructed, or at any
subsequent time should it become deranged, include:-
1° A correcting prism similarly placed and actuated in like manner as before
described with reference to the deflecting prism, and which may conveniently be on
the opposite side of the contre mirrors (or prisms).
20 Attaching a prism or prisms of small angle to one or both of the object glasses, or
the construction of the object glass so as to ie optically equivalent to such combination,
with means for rotating the saine.

page_text: 3° An independent prism or prisms of small angle placed in one or both of the
beams of light, and means for rotating the same.
4° The rotating of one or both of the outer mirrors or prisms about an axis
approximately parallel to the line joining the same, and means for effecting such
rotation.
5° For the case in which the object glasses are placed outside the outer reflecting
mirrors (or prisms), a longitudinal (or a side) motion of one or both of the outer
reflecting inirrors (or prisms), and means for effecting the same.
Go Mounting or grinding eccentrically one or both object glasses, and delicate
means for imparting a rotary motion to the same.
As will be readily understood an instrument constructed according to our Invention,
may be modified in form and arrangement, and some of our before herein referred to
improvements replaced by alternative improvements, without affecting the capabilities
of the instrument.
In one modification of an instrument constructed in accordance with our Invention,
the before mentioned deflecting prism, and the means for moving the same, is replaced
by a peculiar method of supporting one (or both) of the outer reflecting mirrors for
prisms), which permits of the most minute alteration in the inclination of the reflecting
face of the same heing effected with ease and accuracy and means for effecting such
alteration.
This consists essentially in supporting the mirror (or prism) by attaching the ends
or edges of the reflecting surface of the same to the free ends of two hinged arms, (or
pairs of arms), preferably so placed together, that their combined outline is approxi-
mately of the shape of the letter N and a comparatively considerable motion of the
hinged arms, though imparting the same motion of translation to the ends or edges of
the mirror (or prism), alters only to an extremely fine amount the inclination of the
deflecting face, thereby deflecting the rays and causing an alteration in the juxta-
position of the partial images seen through the eye-piece. The means for producing
the motion of the hinged supporting arms and connection to the scale, are of course
suitably modified, though not necessarily altered in principle.
A further modification of our Invention consists in placing the two mirrors at the
ends of the tube, so that their inclined or reflecting surfaces are parallel. One of the
mirrors however is silvered over only half its surface, so as to reflect the rays entering
and reflected towards it from the opposite or other end of the tube; whilst the other
half of the glass is clear, and allows the rays to pass through it directly from the
object being observed. Opposite this same mirror is attached a telescope consisting
of an object glass, one or two defiecting prisms (the one above and inversely placed
with regard to the other, when two are used.) and an eye piece. When the deflecting
prism or prisms are moved to and fro the two partial images seen through the eye
piece are moved towards each other or apart; and when the deflecting prism or prisms
Occupy a certain position (or positions), correct juxtaposition of the partial images is
produced. The arrangements for moving the deffecting prisms and reading the
scale, are also suitably modified, although they may remain the same in principle.
Dated this 29th day of June 1888.
COMPLETE SPECIFICATION.
Improvements in Instruments for Measuring Distances and Angles,
Specially Applicable to Telemeters or Range Finders and other
Analogous Instruments.
We AROHIBALD BARR, professor of Engineering and WILLIAM STROUD professor
of Physics, both of the Yorkshire College Leeds in the County of York, do hereby
declare the nature of this invention and in what manner the same is to be

page_text: performed, to De particularly described and ascertained in and by the following
statement:-
The object of our Invention is to provide an instrument whereby the distances
of moving or stationary objects and in some cases the size of the same may he
easily and rapidly ascertained or indicated with a considerable degree of accuracy,
whilst the base line from which such observation or observations are made may be of
very limited length; such instrument being also capable of measuring or indicating
with like facility and necuracy the angle included by lines of direction which have but
an exceedingly slight inclination with regard to each other; and also the direction and
rate of the motion of moving bodies.
Our Invention further relates to the means for mounting such Instrument for the
special purpose for or to which it may be applied, and for minimising or avoiding any
liability to derangement or damage during use or transport-to means for corroctly
adjusting the same either during construction or at any subsequent time-and lastly
to the combination with it of means for levelling or contouring, or for ascertaining
the azimuth and altitude of objects observed by the instrument.
Our principal improvements are specially applicable to Range Finders for military
and surveying purposes and are hereinafter described chiefly with reference to the
former, but will be evident that they can be readily applied to instruments for other
analogous purposes involving the measurement of distances or angles.
An instrument constructed in accordance with our invention consists of a pair of
reflectors and objectives (or their equivalent) placed at or near the ends of n tube or
frame-piece. These reflectors are so placed that two pencils of rays of light from
the object viewed are refracted and reflected so as to form two images of the object
at or near the centre of the tube or framepiece. Midway between these reffectors are
provided two small reflectors parallel to the first pair, or nearly so, and so disposed as
to reflect the rays of the two pencils to ards one and the same side of the tube or
frame-piece so that both images, or portions of them, may be viewed through one
eye-piece.
In the path of the rays between one of the end reflectors and the corresponding
central reflector is placed a prism of small angle moveable longitudinally along the
tube and which is hereinafter referred to as the "deflecting "prism.
This pris,
preferably so constructed of crown and flint glass as to be chromatic, is placed or
mounted in a guide or sliding frame and arranged to be moved either directly by
hand or by means of rack and pinion, screw or other mechanism. Connected with
this "deflecting" prism, or the mechanism by which it is moved, is a scale for the
purpose of indicating the distance of the object which is being observed or the angle
being measured.
The arrangement just described is such that an object viewed through the instru-
ment is partly seen by reflection from one and partly by reflection from the other
central reflector. It will be evident that by moving the "deflecting" prism_the
image of that portion of the object seen by rays traversing it from the corresponding
end of the instrument, is moved relatively to the image of the other part seen by rays
coming from the opposite end of the instrument. The instrument is so adjusted that
when the "deflecting prism is in a certain position and the rays entering the two
ends of the instrument are practically parallel, the two partial images of the object
viewed appear in correct juxtaposition or alignment, and the scale by which the
distances are read is so marked as then to indicate an infinite distance. When
however the rays entering the two ends of the instrument make an angle with each
other, as for example when an object at a distance (say of 1000 yards) is viewed, the
partial images will not appear in correct juxtaposition or alignment if the "deflecting"
prism he in the position just above referred to; but the partial images may be adjusted
to appear in correct juxtaposition by moving the "deflecting prism to a certain extent
along the tube, and the scale is marked so that in its new position it indicated the
distance of the object, in the case of the example supposed-1000 yards.
"
When in the first example the instrument as arranged for measuring anglos is

page_text: In the
employed, the lines or paths of the rays from the object viewed to the ends of the
instrument being parallel, the scale may then be marked to indicate zero.
second example if the optical length or base of the instrument is say 2 feet, the scale
may then be marked to indicate an angle whose sine is 300ths, i.e. about 2 minutes
17 seconds.
The scale may be of any suitable material, and illuminated directly upon its
graduated face. We prefer however to make the scale of ivory or other suitable
translucent or transparent material and to place it inside the tube, when a tube is used
as the support for the reflectors, and towards the side remote from the observer, and
to illuminate it by transmitted light through an aperture situated behind it, and to
observe it by means of an eye piece or lens situated at about two and a half inches
from the eye-piece used for viewing the partial images. The object of this arrango-
ment is to enable the observer to uso both eyes simultaneously or nearly so, the ono
to observe the object viewed, the other to read the scale. By this arrangement of
scale and scale lens, the necessity of removing the eyes from the instrument in order
to read the scale is avoided.
In order to avoid or lessen any liability to damage or derangement during use or
transport, we prefer to enclose the instrument in an outer tube or case, within which
it is held by elastic or flexible (i.e. non rigid) connections in such a manner, that the
tubo or framepiece of the instrument may not be affected by any distortion of the outer
tube, caused by forces applied to it during use or transport, or by unequal expansion
due to differences of temperature.
To further lessen any liability to deformation of the tube or frame piece of the
instrument during use, the eyepiece (or eye pieces where a second is employed for
reading the indications of the scale), and the guides or portions of the mechanism for
carrying or moving the "deflecting" prism may be attached to the outer case; or if
the guides and mechanism for moving the deflecting prism be supported entirely from
the main tube or frame piece of the instrument, that portion of the mechanism which
is operated directly by the hand may be placed in proximity to one of the points of
support of the main tube (or framepiece), so that forces applied in moving the
deflecting prism produce no appreciable deformation of the instrument. In like
manner and for a like purpose, when the deflecting prism is arranged to be moved
directly by hand, its guido may be supported from the outer case, or from the inner
case in such a manner as to accomplish the same end.
Provision is made in our instrument for two kinds of adjustment. These are herein-
after referred to as the adjustments for "halving" and "coincidence" respectively.
The former is to accomplish the condition that the two partial images of a distant
object shall, when brought into proper alignment, form a complete image and neither
shew duplication nor deficiency of any portion of the object observed. The adjust-
ment for coincidence is the adjustment of the instrument so that when the partial
images of any object are seen in correct juxtaposition or aligment the scale shall
read the true distance of the object observed. Each of these adjustments can be
performed in several different ways according to the means adopted in our Invention.
1°. Eithor adjustment may be made by means of a prism of small angle moveable
longitudinally in the instrument, and acting in a manner similar to that already
described with respect to the "deflecting" prism.
2°. Either adjustment may be made by means of a prism of small angle placed in
the path of one of the beams of light and capable of being rotated about an axis
parallel to the axis of the tube.
3º. When separate reflectors and object glasses are used, either adjustment may be
made by attaching a prism of small angle to one of the objectives, or by mounting
or grinding eccentrically one of the object glasses, and providing delicate means for
imparting a rotary motion to such prism or eccentrically ground or mounted object
glass.
4°. The adjustment for coincidence may be made by moving the scale relatively to
the deflecting prism or moving the scale index so as to alter the reading for any given
position of the "deflecting" prism.

page_text: Ut those alternatives we prefer to effect the "Imlving" adjustment by means of a
prism of small angle situated at some distance from the eye-piece prisms on the side
opposite to the deflecting prism and provided with delicate means for rotating the
same.
To effect the coincidence adjustment, we prefer to move the scale relatively to the
deflecting prism.
The halving adjustment is conveniently effected by observation upon any well defined
object at any distanco from the instrument.
To effect the coincidence adjustment an observation can be taken upon an object at
a known distance, or upon an object at a practically infinite distance, and the sale
made to read accordingly when the deflecting prism has been so adjusted as to bring
the partial images of such object into correct alignment. We provide however
special means for effecting such adjustment with accuracy and facility. It will be
observed that it the object viewed be at infinite distance, the rays entoring the
instrument will be parallel. But we may also obtain parallel beams of light by
observing upon two objects at a distance apart equal to the base length of the instru
ment (ie. the distance between the contres of the reflectors). The apparent coincidence
of these objects is evidently not influenced by their distance from the instrument and
hence their distance need not be known. The coincidence adjustment may thereforo
be made by causing the scale to indicate an infinite distance when the images of such
objects appear in coincidence. To provide such an arrangement always at band, wo
fix narrow nickel plated rings (or other suitable marks easily seen from a distance) on
the outor tube or case at the required distance apart so that two range takers having
instruments of equal base length and observing simultaneously upon each others instru-
ments at any convenient distance apart, may put their instruments into correct
adjustment. Tho exact distance at which the marks require to be fixed is found by
trials or may be determined from the construction of the instrument. Such marks
may also be conveniently placed on the leather carrying case of the instrument, or on
a short staff, or a rod of the base length may be provided for the purpose.
During use, the instrument may be held in the hand, or it may be supported on
n stand of any suitable form. When the instrument is to be employed as a military
range-finder, wo prefer, for the sake of greater convenience and facility for use, to
provide a clamp which can be instantly attached to the nose-block or the barrel of the
rifle, and to which the range finder can be secured, when required, by means of a
spring clip, preferably arranged to swivel on the said clamp. The clip may be arranged
to take hold of a short pieco of tubo surrounding the outer case at the centre of its
length and within which the outer case may be rotated.
To enable the observer rapidly to direct the instrument upon any object whose
distance is required, the opening or window already referred to behind the scale
may be extended abovo or below the latter, so that the eye which reads the scale cau
command a comparatively wide field of view through such window and through a
small hole beside or pierced through the scale lens or eyo piece. A pointor or other
index within the limits of such window may be provided so as more accurately to
define the point in the field of view towards which the instrument is directed, and
this index may be arranged to appear in focus by light traversing the scale lens, whilst
the eye also receives light directly from the distant object through the small hole just
referred to. By this arrangement the index is seen in focus and apparently projected
upon the distant object, and the parts are so disposed relatively to each other, that
when the pointer appears to touch any object, that object will be found in the field
of view of the other eye-piece (ie. that for the reflectors).
It will be evident that the instrument as above described for measuring distances
will be useful for many operations in surveying; for example-the position of a
boat relatively to a coast may be rapidly determined by measuring from the bont with
the range-finder, in the manner above described, the distances of two or more
well defined objects, whose positions relatively to the const are well known. In
this way the instrument may be used for hydrographical surveying.
To adapt the instrument for contouring and other surveying operations, we

page_text: support it upon a stand similar to that of an ordinary theodolite, and provide a
horizontal circle with means for levelling the same and with vernier for reading
azimuthal angles, and a vertical circle or arc, when desired, for reading angles of
altitude and indicating the difference between the actual distance of the object and
its horizontal distance as is common for theodolites. The vertical circle or arc must
evidently be arranged with its plane at right angles to the tube or frame-piece of
the instrument, instead of being parallel to the tube as in the ordinary theodolite.
The tube of the telemeter, or the outer tube where one is provided, as above
described, may itself be conveniently used as the horizontal axis or shaft of the
instrument, and may have the vertical circle or are engraved upon itself or attached
to it either temporarily or permanently. For this purpose a Y or cylindrical bearing
or bearings, similar to those of theodolites may be attached either directly to the
upper or vernier plate of the horizontal circle or supported from such plate by a con-
venient form of support, such for example as A shaped frames similar to those of
ordinary theodolites, and the vernier or index for the vertical circle may be attached
to the plate or to the frame supporting the telemeter as may be most convenient. If
more convenient the vertical circle or are may be attached to the upper plate above
referred to, or to the frame supporting the telemeter, and the index or vernier attached
to the telemeter so as to rotate with it. It will be obvious that it is not necessary
that the centre line of the telemeter tube should be directly over, or be intersected
by, the vertical axis of the instrument. The telemeter tube may be conveniently
placed to one side of the horizontal circle (especially if supported only at a small height
above the latter) so that the eyes may have more convenient access to the eye piece
or pieces, where these project only slightly if at all from the telemeter tube.
Instead of a vertical circle such as is commonly used on theodolites, we may
conveniently substitute a clinometer arrangement either attached to the outside of
the instrument, or situated within the instrument. In the latter case the clinometer
arrangement may be conveniently arranged to be read through the lens for reading
the scale. Such a clinometer arrangement, especially when placed inside the tube,
and arranged to be read by aid of the scale lens, may be used with the telemeter
when the latter is not supported upon a spherical stand, and when it is not used in com-
bination with means for reading angles of azimuth, and is then specially useful in enabling
the observer to determine the horizontal distance of the object observed. To that and
the clinometer may most conveniently be graduated to show directly the difference of
hypoteneuse and base as is common on one side of the arcs of theodolites.
Again the instrument may conveniently be pivoted upon a plano table, such as is
used by surveyors, and the ruler of the plane table so connected to the instrument as
to move azimuthally with it. In this way the azimuth and distance of the object may
be rapidly set out on the paper.
A bubble tube may be attached transversely to the instrument tube, either outside
or inside, to indicato when the line of sight is borizontal, so that the instrument may
be used for levelling and contouring. When placed within the tube, the bubble may
be observed through a suitable opening or window, by aid if necessary of a reflector
or lens or both. When used as a surveying or levelling instrument, cross wires or
other indicators may be provided in the plane of one or both of the images, to more
accurately define the line of collimation of the instrument.
A modified form of telemeter constructed in accordance with our Invention consists
in placing the two mirrors at the ends of the tube, so that their inclined or reflecting
surfaces are parallel. One of the mirrors however is silvered over only half its surface,
so as to reflect the rays entering and reflected towards it from the opposite or other
end of the tube; whilst the other half of the glass is clear and allows the rays to pass
through it directly from the object being observed. Opposite this same mirror is
attached a telescope consisting of an object glass, two deflecting prisms (the one
above and inversely placed with regard to the other) and an eye-piece. Instead of
two deflecting prisms, one may be used occupying a portion only of the cross-sectional
area of the tube. When the deflecting prisms are moved to and fro, the two partial
images seen through the eye-piece are moved towards each other or apart, and when

page_text: the deflecting prisms occupy a certain position (or positions) correct juxtaposition of
the partial images is produced. The arrangements for moving the deflecting prisms,
and reading the scale, though suitably modified may practically remain the saino in
principle.
And in order that the nature of our Invention and the manner in which it may be
performed may be more clearly and fully understood, we will now describe it 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 wherein
they occur.
Our Instrument may be used in any position, but for the sake of clearness in the follow-
ing description, we shall suppose the instrument placed and directed horizontally, and we
shall call the side of the instrument next the observer the "back" and the side remote
from the observer the "front" of the instrument. When in such a position
Fig. I is a vertical longitudinal section.

page_text: longitudinally in the tube, and by this means the partial images of an object viewed
are brought into correct juxtaposition or alignment. Connected with the frame F
carrying the deflecting prism is a scale s of ivory.or other translucent or transparent
material situated towards the front part of the instrument. At a distance of
about 2 inches to the left of the eye-piece prisms and eye-lens e is provided a half
lens (see Fig. 4) of such focal length that the scale is conveniently observed by
means of it. Opposite this lens and in front of the scale S is provided a window W.
to supply the necessary illumination for the scale. I is an index, situated behind the
scale. The scalo is placed above the level of the centre of the tube and the window W
is continued beneath the scale as shown at V in Figs. I and IV. h (Figs. II and IV) is a
hole below the half lens j and 12 is the pointer, which is soen projected upon the
object, (whose distance is to be ascertained,) as already explained.
K is a prism of small angle supported in a circular frame K1, the latter being again
supported by the piece Lattached to the tube A. The circumference of the frame K¹
is cut in the manner of a worm wheel and L' is a worm or screw gearing with the
circumference of the frame K. The worm L is supported by bearings on the
piece L and provided with a milled head (Fig. III) by which it may be rotated, so as
to impart a delicate motion of rotation to the prism K for the purpose of effecting the
"halving" adjustment. The edge of the prism should be placed vertical or
nearly so.
To effect the co-incidence adjustment a screw T is provided which is free to rotate
relatively to the frame F, but constrained to move longitudinally with it. This screw
passes through a nut T attached to the scale. The piece upon which the screw T is
formed is prolonged upon the other side of the frame F, as shown by t. This piece t
is of rectangular section and passes freely through a corresponding rectangular hole
in a milled wheel Q supported by suitable bearings within the tube A. Access is
had to the wheel Q through a suitable opening in the tube A, and its boaring is
so arranged that no dust can enter the instrument at that opening. It will he
evident that when the wheel Q is rotated, the scale S is moved relatively to the
deflecting prism D, so that if the latter be brought into such a position that
the partial images of an object at a known distance appear in proper juxtaposition or
alignment, the scale may be adjusted to indicate the true distance of such object, and
thus bring the instrument into correct adjustment for "coincidence." This adjustment
may also be effected by means of marks upon another range-finder or other object,
in the manner already described, the scale being adjusted to read infinity when the
alignment of the images of the marks has been attained. The nickel plated rings r
at a distance apart equal to the base length of the instrument are provided to facilitate
the adjustment of other instruments of the same base length by this method. The
exact distance at which such marks require to be fixed may be determined from the
construction of the instrument, or by so adjusting the distance between the marks by
trials, that they shall appear in coincidence for the same position of the deflecting
prism at whatever distance from the instrument they are held, (the line joining the
marks being maintained parallel to the instrument). The distance so determined is
that which has been above referred to as the optical length or base of the instrument.
The divisions of the scale may be obtained in the following manner :-The
distance of any particular division from the mark representing infinity is the product
of the base length into the focal length of the objective prisms or lenses divided
by the product of the distance of the object corresponding to the division and the
angle of deviation of a ray traversing the deflecting prism, the latter being expressed
in circular measure. Or in the following manner:-A scale graduated in any
convenient way, as for example into 50ths. of an inch, may be put in place of the final
scale, and the readings of this scale taken when alignment is successively made of the
images of two objects at known distances from the instrument, andthus the distance
between the divisions on the scale corresponding to the distances of those two objects
is determined. The remaining divisions can then be readily deduced in the manner
well known for constructing a scale of reciprocals, the distance of any graduation
B

page_text: from the mark representing infinity being proportional to the reciprocal of the
distance which that graduation represents.
B is the outer tube or case of the instrument provided with apertures corresponding
to those in the inner tube. The instrument is supported within the tube B by a
flexible connection consisting of a pin bearing y and by a spherically formed henring a
close to the milled heads M and Q. The pin y is capable of rotating within the end
piece of the outer tube, and is provided with a suitable head or handle y³ by
means of which the instrument may be rotated within tho tube B, when not in use,
so that the apertures in the inner tube may be covered. This arrangement of
support is such that any deformations of the outer case B caused by applied forces,
or resulting from unequal expansion, is prevented from affecting the main tube A,
and further, any forces applied to the milled heads M. and Q during use or adjustment
of the instrument produce no appreciable deformation of the latter. The condition to
be fulfilled being that the inner tube is supported from or by the outer tube at two
points only.
Fig. IX represents a plan and Fig. X a section of the centre portion of the
telemeter is a short piere of tube surrounding the outer ense B at the centre of
its length. is spring clip which may he attached to the tube (, when required.
and to this a clamp is attached by a swivel joint. The clamp is so constructed as
to fit upon the no- block N2 of the rifle or other convenient part thereof. The clip C
has its lower end bent at right angles to catch upon the piece K, (Figs. V and X)
which projects from the tube The piece is made to fit between the flanges
at the sides of K and the similar piece K, as shewn, and is provided with a
spring (of suitable strength bent over to catch upon the piece K and arranged so
as to be readily raised for disconnecting the clip from the telemeter.
Fig XI represents a method of mounting the telemeter so that the angles of
azimuth and altitude of objects viewed may be determined by it. & and represent
respectively the lower or scale plate and the upper or vernier plate of a horizontal
limb similar to that of an ordinary theodolite. These may be mounted upon a stand
in the manner usual in theodolites with levelling screws, clamping and slow
motion arrangements, and with bubble tubes or circular hubble glass for setting the
vertical axis vertical.
represents a bracket or brackets rising from the plate d
against which the tube is held by means of a spring ², catching the projection,
while the projecting piece on the lower side of (enters a corresponding recess in
the plate . The tube and the tube B may carry the one a scale and the other au
vernier for reading angles of altitude above and below the level direction, or
"difference of hypoteneuse and base." In that case provision is made for fixing the
innor tube A in a particular position as regards rotation in the outer tube B.
may conveniently be done by means of a spring attached to the outer tube B and
carrying a pin which fits into a corresponding hole or longitudinal slot in the inner
tube A or parts attached thereto. This pin is preferably situated near to one of the
supports or y. most conveniently near to .c.
This
Fig. 12 which is n section on line XX' shews an arrangement of clinometer for
indicating angles of altitude not of great magnitude, or difference of hypotoneuse and
base.
to is a weight supported by an axis at fixed to the diaphragm ², or to /³
and the piece which carries the mount for the oyo-piece prisms. Attached to the
weight by the pieco n is a scalo m of ivory or other translucent material in the form
of an are.
The scalo is situated preferably towards the right hand side of and
illuminated by the window. An index attached to the diaphragm h, or to the cross
picco carrying tho indices I and 12, is provided for indicating upon the scule. The
seale may be graduated to shew angles or "difference of hypoteneuse and base," and
may be conveniently observed through the lens j, which for simplicity is omitted from
the figure.
We do not limit ourselves to the precise details shewn in the drawings, as it will
be evident from the former part of this present complete and our provisional specifi-
cations, that such dotails may be varied without doparting from the nature of our

page_text: Also
Invention or affecting the capabilities of the instrument. For example we may us
separate objectives and reflecting prisms, or objectives and mirrors instead of the
compound objective prisms P, P. Also instead of formin; the images of the object
viewed at such positions (before the rays reach the eye-piece prisms) as i², shown
in the drawings, we may so arrange the base length and the focal length of our
objectives or objective prisms, t'at the images are formed within or behind the eye-
piece prisms, in which case the diaphragms d d may be dispensed with, and the
faces of the prisms may be ground at right angles to the plane of contact.
instead of a lens being cemented to the back face of the eye-piece prisms, lenses or
portions of lenses may be cemented to the faces first traversed by the light, or the
eye-piece prisms may be ground spherically upon one or both of their surfaces traversed
by the light, so as to he optically equivalent to a lens and reflector. In these cases to
prevent loss of light owing to obstruction by the plane of contact of the eye-piece
prisms. the centres of curvature c, (see Fig. 5 which represents an elevation
corresponding to Fig. 1) of the spherical faces of the upper and lower prisms, or of
the lenses cemented to the prisms, may be respectively placed slightly above and
below the plane of contact of the prisms. Or again we may use rectangular reflecting
prisms or mirrors and either an inverting or erecting eye-piece, which may be
supported from the outer case, when one is used, so that forces applied to it, do not
affect the main tube of the instrument. Or again we may attach to the outer case the
mechanism supporting or actuating the deflecting prism, or a portion of it.
We are aware of the patents granted to Patrick Adie, No. 357 of 1860 and
No. 608 of 1863 and the patent No. 12404 of 1886 granted to William Henry
Mahoney Christie, and we do not claim arrangements such as they describe in the
specifications of the above patents.
A modified form of telemeter constructed in accordance with our Invention is
shewn in Fig. 13. The mirrors P, P2, are placed at the ends of the tube, so that
their reflecting surfaces are parallel, inclined at 45° to the axis of the tube and face
each other. The mirror P however is silvered over only half its surface, or is arranged
to cover only half the section of the tube, so as to reflect the rays entering and reflected
towards it from the opposite end by the mirror P2. The other half of the glass P is
clear and allows the rays to pass through it directly from the object observed.
Opposite this same mirror is attached a telescope consisting of the object glass and
the eye-piece e, f, and containing a deflecting prism occupying a half section of the
tube, or a pair of deflecting prisms D, D the one beside and inversely placed with
regard to the other, and each occupying a half section of the tube, and having their
line of separation corresponding to the line of separation of the silvered and
unsilvered portions of the mirror P. These deflecting prisms are mounted in a
fraine F, to which is attached the scale S, the whole arranged capable of being moved
longitudinally along the tube by means of a screw S2 provided with a milled head M.
When the deflecting prisms are moved to and fro, the two partial images seen through
the eye-piece are moved towards each other or apart, and when the deflecting-prisuns
occupy a certain position co-incidence or alignment of the two partial images is
produced. A window is provided for illuminating the scale, and the lens for reading
the scale may be placed in the side of the tube opposite to the window. It will be
clear that instead of the before mentioned mirrors, we may use reflecting prisms with
their reflecting surfaces replacing the mirrors, and in place of the mirror P silvered
over half its surface we may employ a reflecting prism occupying only half the cross
section of the tube. K is the prism for effecting the halving adjustment. It is
moved longitudinally along the telescope tube by means of the screw L³ actuated by
a milled head. The coincidence adjustment may be effected by moving the index I
relatively to the tube.
In order to ascertain the size of an object by means of our instrument the observer
may proceed as follows. 1° Observe the distance of the object say, D, then 2°
adjust the instrument so that one edge of the object in the upper field is seen to
co-incide with the other edge in the lower field. Let the new reading of the scale be,
say D¹. Then if & is the base length of the instrument, the diameter of the object

page_text: D-D¹
יכ
observed is the product of the base length of the instrument into the difference of
the two readings divided by the second reading i.e.
Of course this method
is only applicable within certain limits, for largor objects the difference of altitudo or
azimuth as the case may be must also be taken into account.
For military or naval purposes the rate of advance or retreat of an enemy
can be readily determined by measuring the distance at known intervals of time.
When such motion is not in a direct line towards or from the observer the instrument
must be mounted on an azimuthal circle and simultaneous readings of distance and
azimuth must be taken at known intervals of time, from which both the direction as
well as the rate of motion may be deduced.
Having now particularly described and ascertained the nature of our said
Invention and in what manner the same is to be performed we declare that what we
claim is :-
In reflecting telemetors :-
1° The combination in or on a tube or frame-piece of a pair of reflecting prisms or
mirrors and objective glasses (or objective prisms) carried at or near the two ends of
the tube and a pair of reflecting prisms or mirrors at or near the centre of the tube-
with a moveable deflecting prism for the purpose herein specified.
20 The combination of two reflecting prisms or mirrors placed at or near the
ends of a tube and having their reflecting surfaces parallel to each other or nearly
so with a moveable deflecting prism or prisms for the purpose herein specified.
3 The combination with a moveable deflecting prism or prisms-of two objective
prisms placed at or near the ends of the instrument and having their reflecting
surfaces at about 45° to the axis of the tube and having one or hoth of the surfaces
traversed by the beam of light ground spherically and lenses attached thereto so as to
forin nchroinatie combinations substantially as herein set forth.
4° The combination with a moveable deflecting prism-of a scale made of trans-
parent or translucent material and situated within the tube opposite a hole or window
for the purpose herein specified.
5° The combination with a tuho carrying two pairs of reflecting prisms or mirrors-
of a scale made of translucent or transparent material placed inside the tubo and
opposite a hole or window in the same for the purpose specified.
6 The combination with an eye-piece or lens for observing the images of the
object viewed of an eye-piece or lens placed about two and one half inches from the
former for reading the scale.
7° The combination with the subject matter of claim 6° of an extension of the
opening or window behind the scale and a small hole through or beside the scale lens
or eye-piece for the purpose specified.
The combination with a main tube or frame piece of an outer tube or frame
pieco supporting or carrying the former by flexible or elastic bearings for the purpose
or purposes specified.
go The construction in accordance with claim 8° of the means for supporting
portions of the mechanism for producing alignment of the partial images from the
outer tube or case as and for the purpose herein specified.
10° In accordance with Claim 8° the supporting of the eye-picco or piecos from the
ontor tube as und for the purpose heroin specified.
11° The arrangement of that portion of the mechanism for effecting the coincidence
or alignment of the partial imagos in such a way that the portion of the mechanism
operated by the hand may be in proximity to one of the points of support of the
main tube for the purpose specified.
12 The use of a prism or prisms moveable longitudinally in the tube or on the
frame-piece for effecting either or both of the adjustments for halving and coincidence
substantially as heroin set forth.
18° Whon objectives and separate reflectors are used the combination with one
(or both) objectives-of a prism (or prisms) of small angle, (or the construction of

page_text: either or both objectives so as to be optically equivalent to such combination) provided
with means for rotating the same for effecting either or both the halving or
co-incidence adjustments substantially as herein set forth.
14° The use of a prism or prisms provided with means for rotating the same for the
purpose of effecting either or both of the halving and coincidence adjustments
substantially as herein set forth.
15° The combination with a deflecting prism of a scale moveable relatively thereto,
(or of an index moveable relatively to the tube or framepiece) for the purpose of
effecting the coincidence adjustment.
16° The combination with a moveable deflecting prism of object glasses or objective
prisms so constructed and placed as to form the images of the object observed
separately before the rays by which these images are formed reach the central
reflectors and incans for cutting off portions of the images substantially as and for the
purpose herein set forth.
In reflecting telemeters of the kind herein described and claimed:-
17° The combination with the eye-piece prisons of small prisms in such a manner
that none of the rays by which the portions of the partial images which appear in
contact are viewed are obstructed by the plane of contact of the eye-piece prisms,
or the forming or grinding of the surfaces of the eye-piece prisms, so as to be
equivalent to such combination.
18 The combination with reflectors at the ends of the instrument of eye-piece
prisms at or near the centre of the instrument having either or both surfaces
traversed by the light ground spherically or having lenses attached to either or both
such surfaces.
19° When the eye-piece prisms are constructed in accordance with claim 18°, the
placing of the centres of curvature of the faces of the upper and lower prisms, or of
the lenses cemented thereto, respectively above and below the plune of contact of
the prisms, so that the plane of contact may obstruct none of the light which forms
those portions of the images which appear in contact.
20° The combination with reflectors at the ends of the instrument of a clinometer
supported from the tube or frame-piece of the instrument substantially as and for the
purpose herein specified.
21° The provision on the instrument or other object of marks at a distance apart
equal to the base length of the instrument for the purpose specified.
22 The arrangement and construction of swivelling spring clip substantially as and
for the purpose herein set forth and illustrated in the accompanying drawings.
23° The combination of a telemeter of the kind hereinbefore described and claimed
with arrangements for reading the angles of azimuth or altitude or both of objects
viewed by the instrument substantially as herein set forth.
24° The combination of a telemeter of the kind hereinbefore described and claimed
with a surveyor's plane table substantially as herein set forth.
Dated this 29th day of April 1889
J. CLARK JEFFERSON, A.R.S.M.,
2, East Parade, Leeds, Agent for Applicants.