Variations and Deviations of the Compass.
Year: 1886

page_text: Variations and Deviations of the Compass.
I, ROBERT EDISS HARRIS of Church Street, Chesham, Bucks, Master Mariner 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 this invention is to afford increased facility for ascertaining the
variation and deviation of the Compass when navigating a ship or other vessel.
My invention consists of an improved combination instrument or apparatus
whereby observations may be taken either direct or by shadow or reflection and
either with or without tables.
Fig. 1 of the accompanying drawings shews a view in elevation and partly in
section of such improved combination instrument or apparatus which I construct
in the following manner.
I take an octagonal or other conveniently shaped box (a) and fit the same with
a gimballed stand (b) carrying a horizontal circular plate (c) (hereafter referred to
as the base plate) so arranged as to be nearly flush with the top of the box-
A wormed spindle (d) having a weight (e) attached to its lower end passes up
through the centre of the stand and projects through the base plate-The gimbals
and weight serve to keep the stand and base plate in position while by means of
the wormed spindle the centre of gravity of the apparatus can be raised or lowered
as required.
Mounted upon the base plate is a corresponding plate (f) hereafter termed the
horizon plate representing the horizon and divided like a compass card into points,
half points, quarter points, and degrees-This horizon plate revolves round a small
central collar (g) fitted to or formed on the base plate and has a crutched
support (h) fixed thereto carrying a hour circle (i) representing the Equator Such
circle is divided into 24 hours on each side-each hour being subdivided into six

page_text: equal parts of 10 minutes each-One side of the hour circle when thus marked
represents the Southern-and the other side the Northern hemisphere and in order
to clearly indicate this four rectangular arms extend across the centre of the
circle having inscribed upon one side thereof the words "Southern Hemisphere "-
"Noon Midnight "and on the other the words "Northern Hemisphere"
"Noon"-Midnight" while the time on the Southern Hemisphere is written in
reverse order to that on the Northern Hemisphere See detail views of such hour
circle Figs. 2 and 3.
"
"
Directly between the arms of the crutched support is placed an arc of the
meridian (j) upon which are marked both the north and south latitude.
A pointer (k) is mounted on the boss in the centre of the hour circle formed by
the junction of the four rectangular arms already described and this pointer is
worked by a screw stud (kl) by means of which the pointer can be fixed in any
required position.
From a central line upon such pointer and having its right line resting upon
the pointer projects an arc of a meridian or semicircle (1) for the purpose of
measuring the declination of any celestial body between the equator and the poles.
A movable arm (m) (hereafter termed the regulating arm furnished with a
guide (m) is pivotted at its lower extremity to the centre of such semicircle and
worked by a stud (m²) by means of which it can be moved through the 180 degrees
marked on such semicircle while a cross bar (n) (hereafter termed the objective
arm) is mounted at right angles upon the upper extremity of such regulating arm.
Fitted to the lower end of such objective arm is a small triangular plate (o)
having one vertical and two oblique lines (1. 2. 3) marked upon its face and a
central perforation (4) therethrough (See Fig. 7)-This metal plate forms a sight
vane through which observations can be taken.
Fitted near the upper end of the objective arm is a second sight vane (hereafter
termed "the objective vane") consisting of a triangular frame (p) corresponding
in size with the first sight vane and perforated in each corner so as to allow of
three wires (5, 6, 7) (hereafter termed objective wires) being stretched from the
three corners of the triangle and brought to a point in its centre which point is
called the junction or point of intersection-This second sight vane is used when
observations are made by shadow as such wires project their shadows upon the
face of the first sight vane as presently described.
Or such objective vane may consist of a triangular metal plate corresponding in
size with the sight vane and having one vertical and two oblique slots hereafter
termed objective slots cut therein-These slots are so arranged as to form a point
of junction or intersection in the middle of the triangle in the same manner as the
objective wires already described so that when this form of vane is used such slots
throw three rays of light upon the face of the sight vane instead of the shadows of
the three wires as above mentioned-It will therefore be understood that with my
improved apparatus observations may be taken either direct or by shadow or
reflection Detail views of the sight vane and of both forms of the objective vane
are given at Figs. 11, 12 and 13 of the accompanying drawings Thus to take a
direct observation suppose the box which contains the instrument has been placed
on its stand in a convenient position and the weight set free while the hour circle
is brought to such an inclination with the horizon plate as to represent the
latitude The regulating arm is then moved along till the index pointer coincides
with the declination after which the time pointer is set to the apparent time on
the hour circle.
Now having made use of these three elements latitude, declination, and time
the instrument is moved round with the horizon plate and the eye directed
through the perforation in the sight vane till the celestial body sought be found
The centre of the celestial body is then brought into direct contact with the
junction or point of intersection of the objective wires-The moment this is
accomplished the reading on the horizon plate directly in a line with the ships

page_text: nead is the true course being made the difference between which and the reading
of the standard compass is the deviation for that course east or west.
In order to take an observation by shadow assume that the apparatus has been
placed in position, and set for the three elements latitude, declination, and time as
5 heretofore stated, move the instrument and horizon plate round till the shadows of
the three objective wires or the three gleams of light from the objective slots fall
upon the three lines on the face of the sight vane-
-Then so soon as they coincide
read off the bearing of the ships head both from the instrument and the standard
compass and apply as before.
If the shadows of the wires or the gleams of light do not coincide with the lines
on the face of the sight vane then there is either an error in the time used or the
latitude is wrong.
The declination can of course be always found sufficiently correct for these
observations.
In order to provide for observations being made by reflection-a small tube (9)
(termed a telescopic reflector) is fitted either to the upper extremity of the
objective arm or in any other convenient position at an inclination of 45° with
the objective arm This tube has a slot (8) in the front to admit the light of any
given celestial body and is provided with two reflectors an upper and a lower
one (r. 8) which can be used either singly or in conjunction with each other-
When the lower one is used by itself an object is inverted but when both reflectors
are used together the object is seen in its natural position-A sight (t) is fitted. to
or formed on the top of the telescopic reflector.
If preferred the reflectors can be dispensed with altogether and the tube which
contains them used as a simple sight vane for direct observations-This is done by
directing the eye to the sight and viewing the object through the slot in the front
of the tube.
The manner of taking an observation by reflection with my improved apparatus
is as follows-Set the apparatus for the latitude, declination, and time, then move
the instrument round and look through the sight on the top of the tube-So soon
as the sight and reflectors are in the plane of the azimuth circle of the celestial
object selected, its light is received by the upper reflector from whence it is
transmitted to the lower reflector and the observer directing his eye through the
sight to the surface of the lower reflector discovers the object of his search The
moment this happens read off the instrument and compass as before-The further
use of the telescopic-reflector will be hereafter explained.
Figs. 4. 5. 6. shew the telescopic reflector in three different positions the object
observed having the same altitude.
Fig. 4 shews an observation by simple reflection, the object being inverted The
lower reflector (8) is here set at an angle of 45° with the object.
Fig. 5 shews an observation by dual reflection the object being seen in its
natural position-The upper reflector (r) is set at an angle of 45° with the object―
In this case the position of the telescopic reflector is changed 45° from the position
at Fig. 4-This is the position employed when the instrument is used without
tables
.
Fig. 6 shews a direct observation the reflectors 8, and r, being dispensed with―
The position of the telescopic reflector is here changed 22° from the position shewn
at Fig. 5 and 671° from the position at Fig. 4. Either one of these 3 positions may
be employed when the instrument is used with tables.
As already stated my improved apparatus can be used either with or without
tables but when tables of bearings are used the crutched support, meridian circle,
for measuring, latitude, hour circle, and declination are can be dispensed with.
In lieu of these parts a revolving azimuth pointer (u) observing column v
elevation plate v¹ and quadrant, are employed-This arrangement is shewn at
Fig. 8-The azimuth pointer is mounted on the bearing in the centre of the horizon
plate which in the other arrangement is used to carry the crutched support and is

page_text: secured by means of a clamp screw * after which it is set to the bearing of any
celestial body from Burwood's or any other suitable tables.
The observing column is fitted to the base of the azimuth pointer and may either
be fitted with the telescopic reflector as shewn at Fig. 9 or with the objective arm
together with its sight and objective vanes as shewn at Fig. 10-The elevation
plate is pivoted on the top of the observing column and is fitted with the
quadrant for adjusting its position-The objective arm and the sight and
objective vanes and wires are secured to the elevation plate by a screw
can be easily removed and the telescopic reflector secured in like manner.
This
In order to take an observation with my improved apparatus in this modified
form proceed as follows: Having set the azimuth pointer to a bearing from
Burwood's or other tables screw up the central clamp screw so that the horizon.
plate can be carried round with it Then move the horizon plate round till the
right line of the azimuth pointer is in the plane of the azimuth circle, after doing.
which bring the objective arm or the telescopic reflector as the case may be to the
proper elevation and make the observation either direct, by shadow, or reflection in
a similar manner to that already described.
Froin the foregoing description it will be seen that my improved instrument or
apparatus affords great facilities for taking the various observations.
:
"
I would here observe that the novel features of my invention are as follows.
1. The wormed spindle that passes through the gimbals and base plate.
2. The central bearing on the horizon plate.
3. The clutched support with the arc of a meridian attached, and the groove or
Blot for regulating the hour circle.
4. The hour circle with the time written on both sides to represent the Northern,
and Southern hemispheres.
5. The declination are or semicircle with its right line resting upon the time
pointer.
6. The triangular sight and objective vanes.
•
7. The three objective wires and three objective slots.
8. The telescopic reflector.
9. The observing column plate and quadrant.
By this improved construction of instrument or apparatus the following
advantages are obtained.
1. THE WORMED SPINDLE.
The wormed spindle has three distinct advantages-1st The centre of gravity
can be raised or lowered according to the weight used above the horizon plate
2nd Being enabled to lower the weight below where a heavier weight would be
carried the weight used is reduced to nearly one half the size-3rd when the
instrument is out of use the weight is raised by means of the wormed spindle thus
bringing the lower part of the apparatus into a very small compass and reducing
the size of the box which contains it quite one half-This for portable purposes is
a great convenience.
2. THE HORIZON PLATE.
The only novel feature in the horizon plate is the central bearing which enables
the more scientific parts of the instrument to be removed at pleasure without the
aid of pins or screws of any kind-This affords great convenience because the
The only novel feature in the horizon plate is the central bearing which enables
the more scientific parts of the instrument to be removed at pleasure without the
aid of pins or screws of any kind-This affords great convenience because the
cumbrous parts of the instrument can be left on deck and the lighter parts removed
to the cabin The central bearing admits of the crutched support, and all the other
parts of the instrument attached thereto being carried round with the horizon
plate when seeking for a celestial body,

page_text: 3. THE CRUTCHED SUPPORT.
The crutched support is so fitted that it can be secured to the horizon plate by
simply dropping it on to the central bearing of the horizon plate-When the
scientific parts are removed they may be placed in a box and taken below whilst
the gimbals, weight, wormed spindle and horizon plate are left on deck on the
stand and covered over by the cover of the box that contains them The fitting of
the crutched support as before mentioned allows that part of the instrument which
is used without tables to be removed for the purpose of enabling the observer-if
he so desires to use that portion of the instrument which is used with tables.

page_text: Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed I declare that what
I claim is
1. The improved construction and arrangement of apparatus for finding the
variation and deviation of the compass either with or without tables on any course
and in any part of the world substantially as hereinbefore described and shewn at
Figs. 1, 2, 3, 5 and 7, and 11. 12. and 13 of the accompanying drawings.
2. The modified construction and arrangement of such apparatus substantially as
herein before described and shewn at Figs. 4, 5, 6, 8, 9 and 10 of the accompanying
drawings.