An Improved Departure Rule or Instrument for Ascertaining Distances.
Year: 1888

page_text: Date of Application, 10th Ápr., 1888
Complete Specification Left, 8th Jan., 1889
Complete Specification Accepted, 12th Feb., 188
RESERVE
An Improved Departure Rule or Instrument for Ascertaining
Distances.
I, JOHN ALEXANDER MAC LELLAN, of Sentinel Works, Polmadie, in the County
of Renfrew, North Britain, Engineer, do hereby declare the nature of this Invention
to be as follows, that is to say :-
My said Invention has for its object to provide an improved, simple, and convenient
instrument for ascertaining distances, and which can be used on board ship for
determining distances of headlands, lighthouses, or other fixed objects.
A third
My improved departure rule comprises a main bar or ship's-course bar having "
jointed to one end of it a bar hereinafter referred to as the second bar, and which can
be fixed in any position inclined to the main bar by a pinching screw nut.
bar is jointed to a piece fitted to slide on the main bar and can also be fixed in any
angular position by a. pinching screw nut. Every one of the three bars has marked
on it one or more scales, such scales being adapted to suit the particular purposes for
which the instrument is intended. Thus if the instrument is to be used on board
ship one scale on each bar may be conveniently marked with inch divisions to represent
miles for comparatively near objects or slow speeds of the ship, and a second scale with
half-inch divisions for more distant objects or quick speeds.
In using the departure rule on board ship the main bar is held or rested so as to be
parallel to the ship's keel, and the second bar is set to the bearing or direction in
which a headland or other fixed point is seen, the ship being moving towards a point
abreast of such fixed point. Then after a convenient interval during, which the ship
must be kept on a straight course, the third bar is set to the new bearing or direction
of the same fixed point; and the sliding piece with the third bar fixed in its angular
position is moved along the main bar to the point on the main bar scale corresponding
to the miles or distance run by the ship between the two observations. The second
and third bars will then at the point at which their edges cross each other show the
distances of the headland or fixed point from the two positions of the ship. Further,
if the crossing point on the second bar is noted, and the third bar is set at right

page_text: angles the main bar and is moved along that bar until its edge touches the noted
point on the second bar, the distance then marked by that point on the third bar
will be the distance at which the ship was from the fixed point when abreast of it.
Compass dials may be advantageously attached at the joints of the second and
third bars, and may be set to the ship's course; in which case the dial on the
sliding piece will show the bearing of the headland or fixed point when the ship was
abreast of it.
Dated this Ninth day of Anvil 1988
COMPLETE SPECIFICATION
An Improved Departure Rule or Instrument for Ascertaining
Distances.
I, JOHN ALEXANDER MAC LELLAN, of Sentinel Works, Polmadie, in the County
of Renfrew, North Britain, Engineer, 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, that is to say :-
My said Invention has for its object to provide an improved, simple, and convenient
instrument for ascertaining distances, and which can be used on board ship for
determining distances of headlands, lighthouses, or other fixed objects.
My improved departure rule is shown on an accompanying sheet of explanatory.
drawings, figure, 1, being a plan, and figures, 2, and 3, edge views, each showing
the instrument as seen from the side at which the figure is placed. The same reference
letters are used to mark the same parts wherever they are repeated.
The instrument comprises a main bar, or ship's-course bar, A, having jointed to
one end of it a bar, B, hereinafter referred to as the second bar, and which can be
fixed in any position inclined to the main bar, A, by means of a pinching screw
nut, D, the joint being made like that of an ordinary measuring rule or in any other
.convenient way. A third bar, C, is jointed to a piece, E, fitted to slide on the main
bar, A, and can also be fixed to the piece, E, in any angular position by a pinching
screw nut, F, whilst the piece, E, can be fixed at any part of the main bar, A, by a.
separate pinching screw nut, G. The sliding piece, E, is made with an opening, H,
and index point to show on the main bar, A, the precise position of the centre of the
joint of the third bar, C.
:

page_text: Every one of the three bars, A, B, C, has marked on it one or more scales, such
scales being adapted to suit the particular purposes for which the instrument is
intended. Thus, if the instrument is to be used on board ship one scale on each bar
may be conveniently marked with inch divisions to represent miles for comparatively
near objects or slow speeds of the ship; and a second scale with half-inch divisions
for more distant objects or quick speeds.
In using the departure rule on board ship the instrument is held or rested with all
the bars horizontal, and with the main bar, A, parallel to the ship's keels; and the
second bar, B, is sot horizontally to the bearing or direction in which a headland or
other fixed point is seen, the ship being moving towards a point abreast of such fixed
point. Then after a convenient interval during which the ship must be kept on a
straight course, the third bar, C, is to be set to the new bearing or direction of the samo
fixed point; and the sliding piece, E, with the third bar, C, fixed in its angular
position is to be moved along the main bar, A, to the point on the main-bar scale
corresponding to the miles or distance run by the ship between the two observations.
The second and third bars, B, C, will then at the point at which their edges cross each
other show the distances of the headland or fixed point from the two positions of the
ship. Further, if the crossing point on the second bar, B, is noted, and the third
bar, C, is set at right angles to the main bar, A, and is moved along that bar until its
edge touches the noted point on the second har, B, the distance then marked by that
point on the third bar, C, will be the distance at which the ship was from the fixed
point when abreast of it."
Compass dials may be advantageously attached at the joints of the second and
third bars, B, C, and may be set to the ship's course, that is with the direction of the
ship's course parallel to the main bar, A. With such dials the bearings of the fixed
point will be indicated; and when the third bar, (), is placed at right angles to the
main bar, A, the dial at the joint will indicate the bearing of the fixed point when the
ship was abreast of it.
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 :-
An improved departure rule or instrument for ascertaining distances consisting of
parts constructed and combined substantially as herein before described and as shown
in the accompanying drawings.
Dated this Seventh day of January 1889.
EDMUND HUNT,
Applicant's Agent.