APPARATUS FOR TAKING AZIMUTH SIGHTS

Abstract: A circular housing 12 has a transparent panel 30 and is gimbal-mounted on a ship's compass or compass repeater on bearings 24. The housing 12 contains a frusto-conical mirror surface 22 and scale cards 14, 16 having laterally-­ inverted numerals. The lower card 14 is main­ tained in a fixed orientation by the compass. The upper card 16 is fixed relative to the ship. To take an azimuth sight, a pin 20 at the centre of the panel 30 is aligned with the sighted object and bearings from the cards 14, 16 read-off in the mirror diametrically opposite the user's eye. The curvature of the reflections of graduation lines lying to each side of the correct line assist the user. In modified forms of the apparatus, a cylindrical mirror surface 54 extends from the top of the surface 22 and the pin 20 is dispensed with.

Description: APPARATUS FOR TAKING AZIMUTH SIGHTS DESCRIPTION The invention relates to the taking of azimuth sights. It is conventional to provide on ships a compass, and usually several compass repeaters, in each of which a graduated scale rotates relative to the ship to maintain a predetermined orientation to enable the bearing of the ship to be read. So that such a compass or compass repeater can be used for taking bearings of terrestrial or celestial objects an azimuth circle may be provided. The azimuth circle is a separate piece of apparatus which can be placed on the compass or repeater housing for manual movement thereon. The azimuth circle includes sighting means and is moved to align these with the object, the bearing of which can then be read from the scale. It is a disadvantage of such arrangements that the azimuth circle is a separate device which must be movable relative to the compass or repeater. Both pieces of apparatus must have bearing surfaces which must be maintained in good condition. The invention accordingly provides an apparatus for taking azimuth sights, the apparatus comprising a graduated scale and reflective means within a housing having a transparent panel, the reflective means being such that a user viewing a distant object can correlate the object with an image of a portion of the scale seen through the transparent panel from which scale the bearing of the object can be read. The reflective means is preferably arcuate or circular and positioned to reflect at least a portion of an arcuate or circular scale. The reflective means can comprise a frusto-conical mirror with its larger diameter end overlying a circular card bearing the graduated scale so that an image of the scale can be viewed by looking across the smaller diameter end of the mirror at the distant object. The bearing can be taken by means of a sighting element, for example an upright pin, located axially of the mirror, but additionally or instead use can be made of image distortion introduced by the mirror which has the effect of making only a graduation line viewed diametrally across the mirror appear precisely vertical. In a modified form of apparatus, the mirror has a right cylindrical portion extending upwardly from the smaller diameter and to allow an image of a centrally located sighting means to be seen together with the scale image. The housing of the apparatus of the invention will typically be gimbal mounted on a ship deck. The graduated scale will normally be a circular card driven to maintain a fixed orientation but a circular scale fixed with respect to the ship may be provided instead or as well. Advantages of the invention are that it can be embodied in a single apparatus whereas the prior art required two separate parts and that the single apparatus is robust and simple both to make and to use. Since apparatus according to the invention does not need to be turned in azimuth, the apparatus can be formed with substantially no moving parts. For this reason, the apparatus can be sealed against entry of dirt and spray. The apparatus can be incorporated into a compass or compass repeater on a ship's deck and need not be removed and returned under cover after use, as is the case with the known apparatus. Embodiments of the invention will now be described by way of example with reference to the drawings, in which: Figure 1 is a somewhat schematic, vertical, sectional view of an apparatus for taking azimuth sights, Figure 2 is a plan view of two scale cards of the apparatus of Figure 1, and Figures 3 and 4 are views similar to Figure 1 of modified apparatuses. Figure 1 shows an apparatus 10 which includes a circular housing 12 in which graduated scale cards 14,16 are supported. The lower scale card 14 is of larger diameter than the upper card 16 and is maintained in a fixed orientation by a compass or compass repeater in the conventional manner by means not shown. The upper card 16 is fixed relative to the ship on which the apparatus is mounted. Both scale cards 14,16 have graduation lines extending radially inwards from their peripheries (see Figure 2). An upper wall portion 18 of the housing 12 tapers inwardly towards the top of the hdusing 10 and its inner surface is polished to provide a frusto-conical mirror surface 22 spaced from the graduation lines on the scale cards 14,16. The numerals indicating degrees on the scale cards 14,16 are laterally inverted (see Figure 2) so that they can be read normally after reflection in the mirror surface 22. The housing 12 has an open circular top which is closed by a downwardly dished transparent circular panel 30, conveniently made from glass or plastics material. At its centre the dished panel 30 carries an open sight 20 in the form of an upright pin tapering to a point at its upper end. A lower part of the housing 12 has bearings 24 allowing the apparatus to be gimbal mounted on the ship's deck. Figure 2 shows the scale cards 14,16 having graduation lines signifying angles and reversed figures indicating degrees. For clarity, only some of the graduation lines and figures are shown. To take the bearing of a terrestrial object from the ship on which the apparatus 10 is mounted, the sight 20 is aligned by eye as shown in Figure 1 with the object and the bearing of the object is read-off from the scale cards 14,16 reflected in the mirror surface 22 at the point diametrically opposite, the upper card 16 providing a bearing relative to the ship and the lower card 14 an absolute bearing. Because of the curvature of the mirror surface 22, the images reflected by the surface 22 of the graduation lines of the scale cards lying to each side of the graduation line which is diametrically opposite the user's eye will be curved and only the line which is diametrically opposite will provide an image which is a rectilinear. Accordingly, the graduation line on each respective scale card 14,16 which corresponds to the bearing of the sighted object can be identified and, indeed, the sight 20 may be dispensed with, as shown in the modified apparatus of Figure 4. Figure 4 shows an apparatus 40 which is identical to the apparatus 10 shown in Figure 1 except that the sight 20 is omitted. The elements of Figure 4 are indicated with reference numerals identical to the corresponding elements of Figure 1. To take a bearing using the apparatus 40 of Figure 4 an identical procedure to that described above for the part 10 of Figure 1 is followed except that the correct bearings of the object sighted are identified by the images of the graduation line which appear as straight lines in the mirror surface 22. Figure 3 shows another modified apparatus 50 and corresponding elements are again indicated by the same numerals as in Figures 1 and 4. The apparatus 50 is identical to the apparatus 10 of Figure 1 with the exception that its housing 12 has a cylindrical upper wall portion 52 which is polished on its inner surface to provide a further cylindrical mirror surface 54 and that the open sight 20 of the apparatus 10 is replaced by a shorter cylindrical pin 56 also tapering to a point at its upper end. To take a bearing using the apparatus 50 of Figure 3 a similar procedure to that described above for the apparatus 10 is followed except that the image of the pin 56 in the cylindrical mirror surface 54 is aligned with the sighted object and the bearings are read from the images of the scale cards in the frusto-conical mirror surface 22, the correct bearings being those corresponding to the graduation lines directly beneath the image of the pin 56 in the cylindrical mirror surface 54. As before, the identification of the correct graduation line is assisted by the images of the lines to each side of the correct line being distorted in the frusto-conical mirror surface 22. The apparatus 10 or 50 shown in Figure 1 or Figure 3 may be conveniently fitted with a conventional attachment for taking bearings of celestial objects or objects exposed to glare. The attachment has a socket which is fitted over the pin 20 or 56 for rotational movement relative to the housing 12 of the apparatus 10 or 50. The attachment includes a glass panel, which may be a magnifying lens, having a sighting line for alignment with the sighted object and preferably includes a coloured reflector plate which is movable into a position in which it protects the user's eyes from glare. The attachment may also include means, for example a spirit level, for adjusting the apparatus on its gimbals into a horizontal position. It should be noted that the user of the apparatus described does not need to place himself and his eye close to the apparatus. A reasonably accurate bearing can be obtained by a user standing as far as 0.5m away from the apparatus. Moreover, the apparatus is particularly simple to use and instruction of the user prior to use of the apparatus need be only brief.

Claims: CLAIMS 1. An apparatus for taking azimuth sights, the apparatus comprising a graduated scale and reflective means within a housing having a transparent panel, the reflective means being such that a user viewing a distant object can correlate the object with an image of a portion of the scale seen through the transparent panel from which scale the bearing of the object can be read. 2. An apparatus according to claim 1 in which the reflective means comprise a frusto-conical mirror with its larger diameter end overlaying a circular card bearing the graduated scale so that an image of the scale can be viewed by looking across the smaller diameter end of the mirror at the distant object. 3. An apparatus according to claim 2, having a sighting element, located axially to the mirror. 4. An apparatus according to claim 3 in which the sighting element is an upright pin. 5. An apparatus according to claim 3 or claim 4 in which the mirror has a right cylindrical portion extending upwardly from the smaller diameter and to allow an image of the sighting element to be seen together with the scale image. 6. An assembly of an apparatus according to any one of claims 1 to 5 and a compass or compass repeater, the scale being coupled with the compass or repeater to be maintained in a fixed orientation relative to the direction-indicating element of the compass or repeater. 7. An assembly according to claim 6 in which the apparatus for taking azimuth sights includes a further graduated scale which can be maintained, in use of the assembly, in a fixed orientation relative to a structure on which the assembly is mounted. 8. An apparatus for taking azimuth sights, the apparatus comprising a curved graduated scale and reflective means arranged to provide an observer with an image of part of the scale for correlation with an object remote from the apparatus, characterized in that the reflective means is curved to extend around the scale to permit selection of an image of a part the scale for correlation with the distant object.

Inventors: VOUSDEN, JAMES BERNARD
Applicants: S.G. BROWN LIMITED, VOUSDEN, JAMES BERNARD
Application year: 1983
Main classification: G01C1
IPC codes: G01C1