Patent GB-634737-A (GB)
Title: Improvements in or relating to devices for use in astro-navigation
IPC: G01C21/02
Filed: 1947-05-30
Abstract: 634,737. Calculating-apparatus. CASTLE, G. L. May 30, 1947, Nos. 14417 and 25751. [Class 106 (i)] A device for use in astro-navigation comprises an element which is set in a position dependent on the declination and hour angle of a selected heavenly body, two concentric rotatable members co-operating with each other and with a fixed index to give altitude and latitude readings, the relation between which is determined by the set element, and mechanism so interconnecting the element and the rotatable members that a straight line through a selected non-central point on one of the members and through the element is always parallel to a selected radial time on the other member. The device may also be adapted to give an azimuth reading. The principle of the invention is illustrated in Figs. 1 and 2, which are vertical and horizontal views respectively of the celestial sphere. A star lying on the parallel of declination DD and having an hour angle LOS<SP>1</SP>, Fig. 2, is represented by the point S, Fig. 1, and the element referred to above is set at this point. Then if AA is the line through S parallel to the observer's horizon HH, <AOH is the altitude of the star. Thus if the rotatable members have their centre at O and the radial line along HH, the parallel straight line will be AA, and the altitude of the star can be found (for a given latitude) and compared with the observed altitude in the usual manner. General construction. In the device shown in Figs. 3-6, the settable element comprises the head 42, Fig. 11, of a bolt 41 moved by a knob 46, and the rotatable members comprise discs 37, 38, Figs. 4 and 6. The outer disc 38 is rotated by a knob 83 fixed to a pinion 84 on the enlarged end of a bar 85 which is grooved longitudinally to receive the pin 42. The pinion 84 is connected by an idler pinion 86 to a similar pinion 78 on the disc 37, which has slots 79, 81 for the spindles of pinions 84, 86. The bar 85 is thus always parallel to a diameter of the disc 37, which diameter passes through 90 degree marks on a latitude and altitude scale 88 co-operating with a fixed index 91 and an index 89 on the disc 38. On the other side of the device, Figs. 3 and 5, are mounted two slides 29 and 30. The rear slide 29 has a transverse slot 31 and the front slide 30 carries a rotatable disc 32 having a radial slot 33. The bolt 41 fixed to the knob 46 carries a nut 45 and a roller carriage 51, Fig. 11, for sliding engagement with slots 33 and 31 respectively, and a threaded washer 44 so that the bolt can be clamped selectively to the disc 32 and slide 29 by rotating the knob. The slides 29, 30 are further connected by a pin 76 eccentrically fitted on a knob 74 rotatable on the slide 30, the pin engaging circular slots in the two slides. The slot 72 in slide 29 is extended by straight portions 73, Fig. 5, so that when the pin is in the position shown, limited relative movement is permitted between the slides in one direction. The slides may be clamped by a knob 58 on a bolt 54 passing through aligned slots 52, 53. This bolt is fixed to a framemember 21, Fig. 9, and has a nut 57 for engaging the slide 29, and the spring-urged knob has a tapered portion 61 for engaging an enlarged portion of the slot 53 in the slide 30 when a rib 67 engages the deeper of two perpendicular grooves in the head of the bolt. Other forms of linkage and gearing may be used in place of the pinions 78, 84, 86 and the slides 29, 30. Operation. The head 42 is set as follows. With the slides in the central position, Fig. 3, and the slide 30 fixed, the knob 46 is pushed to the outer end of slot 33 and clamped to the disc 32. The disc is then turned until an index 94 lies opposite the declination of the selected star, e.g. 20 degrees, the disc being turned in the direction of arrow 96 or 97 according to whether the declination and the observer's latitude are both in the same sense or not. Movement in the wrong direction is prevented by the pin 76. The knob .46 is then clamped to the slide 29 which is fixed, the slide 30 is released and the disc turned back to zero. This brings the two slides together with slots 31, 33 both along line DD, Fig. 1. The knob 46 is again clamped to disc 32 which is then turned through an angle equal to the hour angle of the star, e.g. 60 degrees. This brings the head 42 to the point S (cf. Figs. 1 and 15), and the device is then turned over, the latitude is set and the altitude read off on the scale 88, Fig. 4. The device can also be used for obtaining the latitude or hour angle in terms of the other values. Azimuth-reading. In Fig. 1 the azimuth equals < SXY, where SX=AB and XY is parallel to HH. To obtain this angle, additional parts are provided including a fixed diaphragm 100, Fig. 17, between slides 29 and 30, having an opening 101 which is concentric with the disc 32 when the slide 30 is in the central position, and a stop 102 slidable on the disc 32 in the direction of slot 33 and secured by a clamp 103. Starting from the position of Fig. 15, the knob 46 is clamped to the slide 29 and the slide 30 is moved to the central position when the slot 33 lies along OS, Fig. 1. The knob 46 is then. clamped to the disc which, with slide 29 is released, is rotated through an angle equal to the co-latitude, thus bringing the line AA along the slot 31 and the zenith axis to the vertical. The knob is again clamped to the slide 29, which is fixed, and the disc 32 is rotated to bring slot 33 in line with slot 31. This causes the stop 102 to be moved inwardly so that its distance from the centre of the disc equals AB, Fig. 1. The stop is then clamped and the slide 30 moved to bring the stop into contact with the head 42 when the centre of disc 32 will be at X and the azimuth can be read against an index 95, Fig. 3.