An Instrument for Measuring Small Angles, which may be Applied to Finding Distances.
Year: 1895

page_text: Date of Application, 12th Dec., 1805
Complete Specification Left. 31st July, 1896-Accepted, 19th Sept., 1896
PROVISIONAL SPECIFICATION.
An Instrument for Measuring Small Angles, which may be Applied
to Finding Distances.
JOHN FRANCIS STUART Lieutenant R.N. H.M.S. Hawke Mediterranean
Station do hereby declare the nature of this invention to be as follows:-
The instrument consists of a diverging lens cut through a diameter, the two parts
being capable of a sliding movement in their own plane.
When the two halves are placed so as to form a single lens the half of an object
viewed through the lens is seen in its proper place in each segment & on moving
one half a certain distance in its own plane the two halves of the object are
separated by a certain angle dependent on the focal length of the lens.
A pointer attached to one half works over a scale attached to the other which
scale is graduated from known angles and thus shows the angle through which the
two parts of the object are separated.
By substituting the distance due to the angle subtended by an object, for the
angle itself on the scale, the distance of the object may be read off immediately.
This instrument may be used by itself or may be placed in front of or behind
the eye-piece of a telescope of any description the graduation being altered
accordingly.
Dated this 12th day of December 1805
W. J. WIGSTON,
Agent for Lieut. J. Francis Stuart, R.N.
JUMI DRIE DITIVATIO
An Instrument for Measuring Small Angles, which may be Applied
to Finding Distances.
JOHN FRANCIS STUART of H.M.S. Hawke in the Mediterranean Fleet a
Lieutenant in the Royal Navy do hereby declare the nature of this invention
and in what manner the same is to be performed, to be particularly described and
ascertained in and by the following statement :-
My invention which is shown in the accompanying drawing consists of a diverging
lens cut through or near to a diameter into two parts A & B. The semilens A or a
part of it is rigidly fixed into a frame C the other semilens B or a part of it is
fixed into a sliding frame D so that its straight edge takes up against the similar
straight edge of the semilens A.
These two edges are kept in contact by means of springs L taking against a
flange M. By means of a screw E worked by a milled out F the sliding frame D
can he made to travel in line with the straight edges of the semilenses. The
sliding frame D works underneath a pointer G rigidly attached to the frame C.
When the two portions of the lens are in their norinal position each half of an
object viewed through the lens is in its normal place in each segment and on
moving the segment B a certain distance the two halves of an object are separated
by a certain angle dependent on the focal length of the lens:
In order to form the scale by which the instrument is read off, a line H. I.

page_text: parallel to the straight edges of the semilenses is ruled on the frame D. and the
place where the pointer G. cuts this line when the two portions of the lens are in
their normal position is marked zero.
The place where the pointer G. cuts the line H I when two objects that subtend
an angle of one degree (or one minute) are brought into horizontal alignment in
the instrument is marked one degree (or one minute).
The position of the pointer G. on the line H. I. corresponding to any number of
degrees (or minutes) is similarly found.
A scale of degrees (or minutes) is thus formed on the line H. I.
A line J. K. is ruled on the frame D. parallel to H. I. at any convenient
distance from it.
A mark is made on the pointer G. where this line cuts it and is labelled any
desired height say 100 feet.
By putting marks on the line J. K. where the pointer cats it when showing the
angles subtended by a height of 100 feet at different distances a scale of distances
is formed on J. K. for this height.
In a similar manner a scale may be formed on any number of parallel lines for
any desired heights.
The angle subtended by any object or a portion of an object or its distance due
to this angle is read by displacing the semilens until the top and bottom of the
object or portion thereof are brought into horizontal aligament.
The instrument may in a similar manner be graduated for the angles
subtended between the sea horizon and an object for my desired heights of eye
and distance.
The instrument may be used with the naked eye or may be fixed before or
behind the object glass of a telescope.
It may also be fixed in front or behind the eye-piece of a telescope of any
description, this will increase the travel of the sliding frame for any given angle
so that the instrument must. be graduated afresh in a similar manner for any
telescope used.
The instrument may be made so that the two semilenses are each movable the
pointer being attached rigidly to one of them.
The advantages I claim for the instrument are that by its means the distance of
an object whose height is known may be read off directly without calculation.
And that the distance of an object between the sea horizon and the observer
when the observers height above the sea is known may also be read off without
calculation.
Having now particularly described and ascertained the nature of my said inven
tion and in what manner the. same is to be performed I declare that what I
claim is
The application of diverging semilenses movable in their own plane to the
purpose of measuring distances directly, substantially as herein described.
Dated this 31st day of Jul 1806
W. J. WIGSTON,
Agent for Lient. John Francis Stuart, R.N.