Year: 1886

page_text: Date of Application, 30th Sept., 1886.
Complete Left, 30th July, 1887.
Complete Accepted, 27th Sept., 1887.
I WILLIAM HENRY MAHONEY CHRISTIE of the Royal Observatory Greenwich in the
County of Kent Astronomer Royal do hereby declare the nature of this Invention to
be as follows:-
The object of my Invention is to provide an efficient instrument which can be
readily used by one man to ascertain distances in range finding or for analogous
purposes.
According to my Invention two pencils of rays of light from an object are received
and reflected and refracted by means of a reflector and object glass placed at each end
of a suitable base or support the two pencils of rays afterwards converging towards
each other from either end of the base or support to form each an image of the object
at or near the middle of the base or support and are there reflected so that the two
images can be viewed through one eye piece.
The object glass or reflector at one end of the base or support is made so that it can
be moved relatively to the object glass or reflector at the other end of the base or
support to cause the image of the object or part of the object received from the object
glass or reflector at one end of the base or support to assume a continuity with or
coincidence with or other relative position with respect to the image of the object or
part of an object received from the object glass or reflector at the other end of the
base or support and the extent of this movement can be utilized to ascertain the
distance of the object in the field of view. This movement and measurement may be
effected by a screw acting on a micrometer slide or on an arm carrying either the
object glass or the Reflector or both.
Dated this 2011
1000
J. HENRY JOHNSON,
47, Lincoln's Inn Fields, London,
Agent for the said William Henry Mahoney Christie.

page_text: I WILLIAM HENRY MAHONEY CHRISTIE of the Royal Observatory Greenwich in
the County of Kent Astronomer Royal 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 my Invention is to provide an efficient instrument which can be
readily used by one man to ascertain distances in range finding or for analogous
purposes.
According to my Invention two pencils of rays of light from one object are received
and reflected and refracted by means of a reflector and object glass (preferably the
latter placed inwards of the former) at each end of a suitable base or support the two
pencils of rays afterwards converging towards each other from either end of the base
or support to form each an image of the object at or near the middle of the base or
support, and are there reflected by means of two reflectors so placed that the two
images can be viewed through one eye piece.
The object glass at one end of the base or support is made so that it can be moved
relatively to the object glass and reflector at the other end of the base or support and
independently of the reflector at its own end of the base or support, and the other
parts of the instrument so as to cause the image of the object or part of the object
received from the object glass and reflector at one end of the base or support to assume
a continuity or coincidence with or other predetermined relative position with respect
to the image of the object or part of an object received from the object glass and
reflector at the other end of the base or support and the extent of this movement can
be utilized to ascertain the distance of the object or objects in the field of view.
This movement and measurement are conveniently effected by a micrometer screw
and slide but they may be otherwise effected for example by a micrometer screw acting
on an arm which turns about a centre and carries or acts on the object glass to move
it about a centre other than its own.
And in order that my Invention may be fully understood I will describe with
reference to the accompanying drawings the manner in which the same may be carried
into effect.
Figures 1 and 2 are longitudinal sections at right angles to each other of an instru-
ment constructed according to my Invention. A is a tube (shewn broken away at
parts to economize space in the drawing) at the outer ends of which are two
openings a a facing which and at an angle of 45 degrees to the axis of the tube A is a
reflector, that at the one end being marked Band that at the other end being marked B³.
These may be conveniently made of plane parallel glass silvered on the back such as is
used in Sextants the situation of the object glasses CC inwards of the reflectors admitting
of the use of such glass. Inwards of these reflectors are two similar object glasses that
at one end of the tube A being marked C and that at the other end being marked (". In
the centre of the tube A at or near the common focus of the two object glasses C C² ar

page_text: two half reflectors one to receive the image of the object or part of the object from
the reflector and object glass at one end of the instrument and the other to receive the
image of the object or part of the object from the reflector and object glass at the
other end of the instrument. These reflectors are marked D D². They may conve-
niently be of Speculum metal. They are situated at right angles to each other and
one above the other at angles of forty five degrees to the longitudinal line of the tube A
and parallel with the reflectors from which they receive the image. In the tube oppo-
site these reflectors D D² is an opening in which is fixed an eye piece E which may
be either an inverting eye piece or an erecting eye piece.
The object glass C is made adjustable in a direction at right angles to the axis of
the tube A by a micrometer screw and slide, f being one member of the slide fixed
in the tube A and g the other member of the slide carrying the mount of the
object glass C which mount may be made adjustable in the part g to fix the distance
of the object glass C from the reflector D longitudinally of the tube A.
The object glass at the other end is shewn as being similarly adjustable longi-
tudinally of the tube A but either one or both of the object glasses CC may be thus
arranged.
H is a slow threaded screw passing through a screw box in the part of and acting
on the part g of the slide to move it in the part the part g being kept in bearing on
the screw H by means of an antagonistic spring or springs or by other arrangement
as is usual in micrometers.
In connection with the screw H is a scale of distances i shewn as being divided on
a disc spirally the front of the disc i being divided into a spirally arranged scale or
series of divisions and as the screw turns through a complete turn the pointer; is
moved through a distance equal to the width between each turn of the spiral. This
may be effected by means of a pin k on the slider 1 of the pointer j engaging in a
spiral groove at the back of the disc corresponding to the spiral scale on its front.
The scale may be otherwise arranged, for example it may be a sliding longitudinal
scale on a toothed rack actuated by a toothed wheel on the micrometer screw.
The divisions of the scale i may be obtained in the well known way of obtaining
such a scale videlicet by considering that the movement of the object glass from the
initial position for objects at an infinite distance is the product of the base (distance
between the centres of the reflectors B B³) into the focal length of the object glass
divided by the distance of the object observed.
Diaphragms may be used as in telescopes to cut off stray light they being situated
in the tube A between the object glasses C and C2 and the reflectors D and D³.
When the instrument is in use it may be situated vertically horizontally or in any
convenient intermediate position.
The tube A may be mounted on any suitable stand and it may be provided with a
mounting which will enable it to be moved in azimuth or in altitude to bring the
object or objects into the field of view. In using the instrument the micrometer
screw is turned until the portions of the object or objects appearing on the
reflectors D D assume an alignment the observation being made as near to the middle
of the field of view as is practicable. A high degree of accuracy of measurement is
attainable by the arrangement of the micrometer screw and slide. For this purpose
the screw should have a very fine thread say 100 turns to the inch.
The tube A should be protected from the heat of the sun as far as possible to prevent
unequal expansion and consequent distortion. For this purpose the tube A may be
enclosed in a casing of wood, metal, or other material with air or other non-conductor
of heat between the casing and the tube.
I do not limit myself to the precise details shewn as it will be evident that they
may be varied, for example the reflecting mirrors (B B³, D D²) may be replaced by
prisms if desired and the mirrors or prisms D D² may be placed not truly in focus,
also the object glasses C C may be placed outwards of the reflectors BB'. The tube A
may be replaced by any suitable base or support. I am aware of the Patents No. 357
of 1860 and No. 608 of 1863 granted to Patrick Adie and I do not claim arrange-
ments such as he describes in the Specification of those Patents.

page_text: Having now particularly described and ascertained the nature of my said Invention
and the manner in which the same is to be performed I declare that what I claim is :-
First. A reflecting telemeter constructed or arranged as hereinbefore described and
illustrated in the accompanying drawings.
Second. In reflecting telemeters of the kind hereinbefore described the combination
with the object glass at one end of the base or support of a micrometer arrangement
and scale of distances whereby the said object glass is capable of fine adjustment
independently of the reflector at the same end and independently of the other parts of
the instrument substantially as and for the purpose herein before described.
Third. In reflecting telemeters of the kind herein before described and claimed the
arrangement of the reflector and object glass at each end of the base or support with
the object glass inwards of the reflector substantially as hereinbefore described and
illustrated.