525,927. Sun compasses. GROVES, W. W. (Clark, J. C.). March 3, 1939, No. 6991. [Class 97 (ii)] [Also in Groups XXXVIII and XL] A compass of the non-magnetic, lightcontrolled type described in Specification 486,679 is adjustable in azimuth to give a constant north-south direction by means responsive to the radiant energy of the sun, which means operates on deviation of the azimuth adjustment from the true north-south line. The compass shown in Figs. 1 and 2 comprises an outer ring 6 rotatable by the electric motor 12 to give the azimuth adjustment referred to above. Secured to the ring 6 are pillars 7 in which a ring 8 is pivoted a further ring 4 being pivoted in the gimbal 8 along an axis 3, at right angles to axis 7. This ring 4 is rotated about axis 3 by a clock device 2. A disc or circular plate 10 is mounted on pivots 5 within the ring 4. This disc carries a vane 11 on each side of which are arranged light-sensitive cells 13, 14, which are connected in a balanced circuit to a two-way relay 15 operation of which, due to unbalance of activation of cells 13, 14, operates the motor 12. The time mechanism 2 is such that the ring 4 turns on axis 3 one revolution in 24 hours ; it thus follows the sun round from east to west. The latitude ring 8 is manually adjusted on axis 7 to correct for the latitude of the position of use of the compass while the declination of the sun at that point is corrected for by swinging the table 10 about axis 5 manually or automatically by means of an electric motor and crank gearing. When the compass has been thus set with the sun's centre in line with the plane of the vane 11, the axis 3 will be the true north-south line. Movement of the instrument about a vertical axis will cause unequal energization of the cells 13, 14 and the azimuth adjustment at once rotates the ring 6 to restore the true north-south bearing. The light impinging on cells 13, 14 may be interrupted by a motor driven shutter so that amplifying stages may be employed between the cells and relay 15, Fig. 18 (not shown) ; or the two cells may be arranged on one side of the vane 11, the shadow of which falls between the two so that the circuit is now balanced for one cell in full activation and the other in shadow, Figs. 3 and 4 (not shown) ; alternatively the vane may be replaced by a sloping rod, the shadow of which normally lies between the two cells the separation between which is adjustable by screws. Figs, 7 and 8 (not shown). In Figs. 5 and 6 the vane 131 is bow-shaped and a second pair of light-sensitive devices 132, 133 control the tilting of the table 130 to compensate automatically for latitude and declination. These devices control motor 135 through relay 134; alternatively this control may replace the time motor 2. In a modification of this latter system a single pair of cells is used, these being periodically switched first into the control circuit of relay 134 and motor 135, then into that of relay 15 and motor 12 ; a rotating shutter is associated with the cells, Fig. 19, (not shown). In the arrangement shown in Figs. 9 and 10 the azimuth adjustment 33 driven by motor 12 carries pillars 32 to which is pivoted a latitude ring 30, a second or time ring 36 is pivoted within 30 on axis 35 and the movable housing 38 is pivoted within 36 on axis 37. A lens 45 focusses the light rays, in the form of a narrow band of light, on a cone-section reflector activating equally the two cells 13, 14 when the rays are truly central. Figs. 12 and 13 show modified construction of the central table 10, comprising a barrel-shaped member 60, 50 into which light is admitted by the arc-shaped transparent segment 61 or the transparent strip 54. Members 55, 56 are reflectors, the light being reflected on to cells 13, 14 over a wide angle of incidence to the rotating member 60, 50 which is mounted for rotation on the usual azimuth adjustment member 6, Figs. 1 and 2.