269,781. James, R. W., (Holmes Navigating Apparatus Co., Inc.). Aug. 23, 1926. Tell-tale apparatus.-An instrument for use on a ship &c. for determining its total lateral deviation from a set course, and the total component distance travelled along the set course, comprises a magnetic compass and a follow-up or master compass which controls a repeater, the movements of which control the driven elements oi two integrating devices, one for recording the deviation and the other for recording the component distance travelled. If the speed of the ship is known the indications of the two integrators can be used to find the position of the ship at any time. The magnetic compass comprises needles 2, 2a supported on a pivot 6 within the bowl 8 and carrying a compass card 10 from which depend two conductors 11, having the shape shown in Fig. 1, and extending into an electrolyte 12 in the bowl. Above the level of the electrolyte the bowl contains mineral oil &c. 13 which does not mix with the electrolyte. The bowl 8 constituting the follow-up member, is provided with four conductors 14 - - 14<c>, and with a compass card 17, and is carried by a frame 24 supported in gimbals 26, 28. The support 18 for the bowl carries a gear wheel 19, adapted to be driven by a pinion 43 on the shaft of the follow-up motor 32, Fig. 1, and also carries contact rings 20, 20<a>, 20<b>, engaging brushes 30, 30a, 30<b>, connected to the conductors 14 - - 14<c>, the conductors 14a, 14b being connected together. The motor 32 has opposed windings 44, 45, the currents to which are controlled by a relay 48 comprising an armature 47 and electromagnets 52, 52<a>. The magnet 52 is connected in series with the conductor 14, electrolyte 12, conductor 11, electrolyte 12, and conductor 14<a>, and the magnet 52a is in a similar circuit including the conductors 11<a>, 14b, 14<c>. When the card moves relatively to the bowl these two circuits become unbalanced, the armature 47 is moved to complete the circuit through one of the windings 44, 45, and the motor 32 thus turns the bowl to follow the card. The current for the windings 44, 45 and magnets 52, 52<a> is derived from an alternating current source 46. Vibration of the armature 47 is prevented by suspended masses 50, 50a. The motor 32 also drives a distributor 41 controlling a step-by-step motor 54 which drives the repeater compass.