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are now being manufactured by the Holmes Navigating Apparatus Co., 48 Cedar St., New York city. They have undergone seagoing tests of an ex- tended nature and are shown installed on an American freighter and tanker in the accompanying illustrations. The path and position indicator is designed to enable the man at the wheel to keep on the set course with greater certainty. It will also serve as a positive and automatic check on the familiar methods of dead reck- oning. It will in effect not only trace the course the ship has followed but it will serve to indicate the position of the vessel at any time in relation to the set course. The magnetic master compass is the controlling unit for the path and position indicator and it is capable of operating electrically one or more repeater compasses without having its own magnetic sensitiveness im- paired. In the precision of its per- formance it is just as dependable as the best master clocks that operate electrically a system of repeater clocks, at the same time losing none of those characteristics or functions essential to its purpose as a naviga- tor’s compass. The inventor spent much time on the bridge of ships studying at first hand the difficulties of navigation. One of these difficulties was the cor- rection for yawing. The cumulative effect of yawing and the uncertain work of the man at the wheel might carry the vessel to one or the other side of the set course, though travel- ing parallel to it. When estimating a ship’s position by dead reckoning, when it is impossible to make sun or star readings, the matter of correcting for yawing becomes a difficult problem. This error under certain conditions of wind and sea may amount to as much as 15 or more miles in the course of a 24-hour run. In certain waters this might mean danger and at all times it is a waste of time and fuel. It was to aid and correcting this difficulty that the two instruments mentioned here were developed. The path and position indicator can be controlled either by a gyro com- pass or by the magnetic master com- pass, as has been established by long voyages at sea, but the instrument was originally conceived as a com- panion apparatus for the magnetic master compass. In this compass the movement of the needle in a special electrolyte alters or unbalances the resistance of two opposing electric circuits through which a weak alter- nating current flows. The needle float carries four platinum electrodes—ter- minals, respectively, of insulated sec- tions of the two opposed electric cir- cuits; and on adjacent sides of the bowl are four segmental plate elec- trodes also of platinum so as not to be injured by the electrolyte. There is always a fluid-filled gap between each electrode on the magnet float and its neighboring electrode on the side of the bowl; and it is the interval be- tween each pair of electrodes varying according to the direction in which the magnet float moves that deter- mines the measure of _ resistance offered to the current as it flows through the opposing or opposite elec- trie circuits. Any angular movement of the mag- net float will upset the normal bal- ance existing between the two cir- cuits when the float is at rest and this unbalancing is utilized to effect a sensitive relay, which in its turn con- trols a small reversible motor. The motor causes a follow-up ring mounted above the compass bowl to turn to the right or to the left so as to bring the markings on the phantom com- pass card in accord with those of the regular card in the bowl. As _ the follow-up ring is thus moved to right or left by the motor, until unison is (Continued on Page 46) AT LEFT—MAGNETIC MASTER COMPASS ON BOARD AN AMERICAN TANKER, CONTROLLING A HOLMES PATH AND POSITION INDICATOR AND A REPEATER COMPASS IN THE PILOT HOUSE. AT RIGHT—PATH AND POSITION INDICATOR ON AMERI- CAN FREIGHTER OPERATED IN CONJUNCTION WITH A GYRO COMPASS 36 MARINE REVIEW—September, 1927.