GB2191579A - Sun compasses - Google Patents

Abstract

A sun compass 10 comprises a base 12 carrying indications 14 associated with time of year, time of day and latitude, and a gnomon 16 upstanding from the base 12 and adjustable relatively to the base 12 in an elongate direction according to the time of year, whereby manipulating the base 12 in a horizontal attitude, such that the shadow 18 of the gnomon 16 passes through a position according to the time of day and the latitude, causes the base 12 to be orientated such that the elongate direction of adjustability of the gnomon 16 lies in the north - south direction. <IMAGE>

Description

SPECIFICATION Sun compasses The present invention relates to sun compasses in contrast to the more familiar magnetic compasses.

A magnetic compass is normally used both on land and at sea to determine rough azimuths or bearings. However, because north indicated by a magnetic needle will differ from true north buy the magneticvariation,thevalue ofthe magnetic variation at the place of observation must be known.

Moreover, the magnetic needle will be affected by masses or deposits of iron, iron ore or similar in the immediate neighbourhood of the place of observation.The existence of such local perturbations in uncharted desert or polar regions may not be known. It will thus be appreciated that a magnetic compass is not always appropriate.

According to the present invention, a sun compass comprises a base carrying indications associated with time of year, time of day and latitude, and a gnomon upstanding from the base and adjustable relativelyto the base in an elongate direction according to the time of year, whereby manipulating the base in a horizontal attitude, such that the shadowofthegnomon passesthrough a position according tothetime of day and the latitude, causes the base to be orientated such that the elongate direction of adjustability of the gnomon lies in the north - south direction.

The user thus needs to know the time ofyear, the time of day and the latitude. Thetime of year, ordate, is easily established, if not already known, by keeping a calendar. The time of day is easily established by keeping a watch or othertime-piece set at local longitudinal time (not G.M.T. unless at 0 longitude). The latitude is easily established, if not already known, for example by solar observations at noon. From this information, the user is able to use thesun compassto establish the north-south direction. From a further knowledge of whetherthe user is in the northern hemisphere or the southern hemisphere, the user is finally able to establish true north.

The accuracy of the sun compass ofthe present invention depends partly on the skill ofthe user and partly on the detail of the information carried by the base.

Preferably, there are markings indicating the time of day cover most ifnotall ofthe hours ofsunlight atthe equator. The range of said markings maycover from 6 am to 6 pm. It is convenient, to avoid visual confusion, if the markings are hourly markings, but the time of day may be divided more or less finely if desired.

Preferably, there are markings indicating the latitude to cover most if not all of the possible latitudes between the equator and the poles. The range of said markings may coverfrom O"to 80".As there are merely minimal differences between the markings for 80" and 90", the sun compass of the present invention may in fact be suitable for use anywhere in the world even though the latitude markings are apparently incomplete. It is convenient, to avoid visual confusion, if the markings are at spacings of 10 , but the latitude may be divided more or less finely if desired.

Preferably, there are markings indicating the time ofyearforall ofthemonthsoftheyear.Said markings may be sub-divided into thirds of months.

Again, thetime of year may be divided more or less finely if desired, primarily dependent on the desirability of avoiding visual confusion.

Conveniently, the indications associated with the time of day and the latitude intersect one another, whereas the indications associated with the time of year are spatially separated therefrom.

A particularly preferred arrangement is forthe above-identified information to be carried on a circular base or at least a circular portion ofthe base.

The circle may be divided around its circumference into bearings of angular degrees, possibly into numbered divisions of 100 separated by unnumbered divisions of 5". The angular bearings may be of value should the user wish to take sightings in directions otherthan true north.

One half of the circle may carry a graph with the time of day markings on the diameter, i.e. X axis and the latitude markings on the radius perpendicularto that diameter, i.e. Y axis. The X axis should be on the linejoining angular bearings of 2700 and 900 and the Yaxisshould be on the line joining angular bearings of00and 1800. Thetime ofday markings will be straight lines parallel to the Yaxis apartfrom at noon whenthetimeofdaymarking istheyaxis.The latitude markings will be curves which approach the X axis at morning and evening and are furthestfrom the X axis at noon.

The other half of the circle may carry an inscribed circle divided around its circumference into identified months. The elongate direction of adjustability ofthe gnomon may beformed as a slot in the base, the slot extending along partoftheyaxis and continuing to extend along all of an aligned diameter of the inscribed circle. The time of year markings will be perpendicular chord-like projections from the circumference of the inscribed circle to the edges of the elongate slot.

The angular bearing, time of day, latitude and time of year markings may all be engraved or otherwise formed directly on the base, although preferably they are all printed orotherwiseformed on a disc which isto be laid upon the base so that a slot inthe disc over-lies the slot in the base.

The gnomon may be a rod projecting perpendicularly to the base. One end of the rod may be detachably connected, for example by a screw thread or push fit, to an upper face of a carrier slidably located with respect to the slot or slots. In one arrangement, that face of the base which is to abut the disc is counter-sunk atthe slot in the baseto produce a portion for locating the carrier which is widerthan the remaining portion of the slot in the base and the superimposed slot inthedisc, thereby effectively sandwiching the carrier between the disc and the base. The carrier may also be provided on its upperface with a marker spaced from the rod. In this case, the carrier is slid along the slot or slots until the marker is positioned according to the time of year markings whereupon the gnomon is in the correct position for shadow casting purposes. A lowerface ofthe carrier may be provided with a threaded stud passing through the slot in the base and engaging a threaded nut, which may be releasablytightened againstthe base to secure the carrier and thus the gnomon in a selected position, the threaded stud and thethreaded nuttogetherforming releasable securement means.

The shadow cast by the gnomon may pass through the intersection of actual time of day and latitude markings, or alternatively through the intersection of estimated markings derived from the actual time of day and latitude markings.

A pair of sights, such as a conventional pin and hoop ortriangularstud and notch with thumb tabs, may be provided on diammetrically opposed parts of a ring, which is rotatablymountedabouttheangular bearing markings on the base orthe disc. It may be possible to store the gnomon, when detached from the carrier, by releasably connecting the gnomon to the pair ofsights. For example, one end of the gnomon could be screwed or pushed into a bore in the triangular stud of one sight with the other end of the gnomon resting in thetriangular notch ofthe other sight. The ring is preferablyfreelyrotatably mounted in an appropriately shaped recess in the base.

It will be remembered thatthe base needs to be manipulated in a horizontal attitude to obtain accurate orientation. It is therefore desirableto provide the base with means for indicating whether ornotthe base is level. Said means may take the form of one or more spirit levels, such as a pair of linear spirit levels arranged orthogonally or a single circularspirit level. In the latter case, in particular, but also in the former case, it may be possibleto locate the spirit level(s) within the area surrounded by the angular bearing markings without losing too much accuracy or obscuring too much information.

If the use of spirit level(s) is not possible, for example in the extreme cold encountered in the polar regions, there could instead be mechanical means for indicating achievement of a horizontal attitude, such as a movable suspended ball to be centered between preferably at leastthree fixed indicators. In some circumstances, it may be sufficientforthe user merelyto carry the base in his or her hands and sense whether or not the base is reasonably level.

Preferably, the base is shaped to be carried and manipulated by hand during use withoutfurther support.

To permit night navigation, the base may be provided with a socket into which a further rod may be inserted so that this further rod in conjunction with the gnomon can be directed atthe north star in the northern hemisphere, or directed at the southern cross in the southern hemisphere.

Preferably,thesun compass of the present invention isas light in weight, as small in bulkand as robust and inexpensive as possible, being no more complex than is necessary to permit accuracy of say up to 10, that order of accuracy being more than adequate for most general users.

Several sun compasses, in accordance with the present invention, will now be further described, by way of example only, with reference to the accompanying drawings, in which: Figure lisa schematic plan view of a sun compass in accordance with the present invention; and Figures2 and 3 are plan views of two further sun compasses, in accordance with the present invention, the latter of which has omitted an information-carrying disc to expose a gnomon-supporting carrier.

Afirstsun compass 10 in accordance with the present invention is shown in Figure 1.

The sun compass 10 comprises a base 12 carrying indications 14 associated with time of year, time of day and latitude, and a gnomon 16 upstanding from the base 12 and adjustable relatively to the base 12 in an elongate direction according to the time of year, whereby manipulating the base 12 in a horizontal attitude, such that the shadow 1 8 of the gnomon 16 passes through a position according to the time of day and the latitude, causes the base 12 to be orientated such that the elongate direction of adjustabilityofthe gnomon 16 lies in the northsouth direction.

The base 12 may be formed of a plastics material and for ease of handling may be contoured as at 20.

The indications 14 may be printed on a cardboard disc, as hereinbefore described, which is secured to a circular portion ofthe base 12 such that a slot 22 in the disc over-lies a slot in the base 12.

The gnomon 16 may project perpendicularly to the base 12 and be adjustable along the slot 22 according to the time of years indicated by a marker 24which lies within the slot 22.

In Figure 1 the marker 24 has been set at 18 February (or 20 October) and the base 12 has been manipulated until the shadow 18 of the gnomon 16 has passed through the inersection of the indications for 2 pm at 20 latitude.

The indications 14 may be surrounded by a ring 26, which is trapped buy a restraint 28 screwed onto the base 12 to be freely rotatably mounted on the base 12 underthe control of diammetrically oppositely arranged thumb tabs 30, to which are secured a pin 32 and a hoop 34 constituting a conventional pair of sights. Beyond the ring 26 may be a socket 36 into which an additional sight (not shown) may be inserted for use in conjunction with the gnomon 16 in night navigation. Even further beyond the ring 26 may be a pair of orthogonally arranged linear spirit levels 38a, 38b for use in checking that the base 12 is being carried in a horizontal attitude.

Figure 2 shows a second compass 40 in accordance with the present invention, which differs from the first sun compass 10 primarily in thatthe linear spirit levels 38a, 38b have been replaced by a single circularspirit level 38,the indications in Figure 2 being identical to those in Figure 1.

Athird sun compass 42 in accordance with the present invention is shown in Figure 3. The same reference numerals to indicatethe same functionally equivalent features will again be used. The disc carrying the information 14 has been omitted to give a clearerview, through a translucent plastics material of the circular base 12, of the arrangement forallowingadjustmentofthegnomon 16. The base 12 may beformed with a slot 44 having a counter-sunk portion for receiving a longitudinally slidablecarrier46.The rod-like gnomon 16 andthe marker 24 are carried by the upper face of the carrier 46. Athreaded stud 48 extends through the carrier 46 and the slot 44 to below the base 12 where it may releasably engage a disc-like nut 50. To provide a smooth surface on which the disc carrying the information 14 can be placed, the upper part of the counter-sunk portion ofthe slot 44 can be closed by a further translucent plastics member 52 having its own slot 54. It should also be noted that in thesun compass 42,the pair of sights on thethumbtabs30 are constituted by a triangular notch 56 and a triangular stud 58.

Claims (12)

1. A sun compass comprising a base carrying indications associated with time of year, time of day and latitude, and a gnomon upstanding from the base and adjustable relativelytothe base in an elongate direction according to the time of year, whereby manipulating the base in a horizontal attitude, such that the shadow of the gnomon passes through a position according to the time of day and the latitude, causes the base to be orientated such that the elongate direction of adjustability ofthe gnomon lies in the north - south direction.

2. Asun compass according to claim 1, in which the indications associated with the time of day and the latitude intersect one another, whereas the indications associated with the time of are spatially separated therefrom.

3. A sun compass according to claim 2, in which the indications associated with the time of day, the latitude and the time of year are in the form of markings lying within a circle,thetime of day and the latitude markings being located within one half of the circle, the time of year markings being located within the other half ofthe circle, and the locations to which the gnomon can be adjusted falling within both halves of the circle.

4. A sun compass according to any preceding claim, in which the gnomon is adjustable along a slot through the base.

5. Asun compass according to claim 3 and claim 4, in which the markings ofthe time of day, the latitude and the time of year areformed on a disc having a slot therethrough in juxtaposition to the slot through the base which is countersunk so thata carrier is sandwiched between the disc and the base with the gnomon extending from one face of the carrierthrough the slot through the dise and releasable securement means extending from an opposed face of the carrierthrough the slot through the base.

6. Asun compass according to claim 3 or claim 5, in which a pair of diametrically opposed sights are mounted for rotation on the base outside the circle circumscribing the markings.

7. Asun compass according to any preceding claim, in which thegnomon is detachable.

8. Asun compass according to claim 6 and claim 7, in whichthegnomon isreleasablyconnectableto the pair of sights.

9. A sun compass according to any preceding claim, in which the base includes level indicating means.

10. Asun compassaccording to any preceding claim, in which the base is shaped to be both carried and manipulated by hand during use without further support.

11. Asun compass according to anypreceding claim, in which the indications of the time of day are in hourly divisions, the indications of the latitude are in 10" divisions and the indications of the time of year are in third of month divisions.

12. A sun compass substantially as herein before described with reference to any one of the accompanying drawings.