Abstract
To decide the ship's position on the chart, the following method sometimes has been used ; select three objects whose positions are accurately given on the chart. With sextants, measure simultaneously the horizontal angles between the center object and the right and left objects, then set angles to the 3-arm protractor. Then place the protractor on the chart with its center at about the estimated position of the ship with the straight edge of the fixed arm passing through the plotted position of the center object. Move the protractor about until the straight edges of the right and left arms pass through the plotted positions of the right and left objects. The center of the protractor is now accurately at the position of the ship at the time the sextant angles were taken. But this method being pretty complicated, it is scarecely used except for the hydrographic survey. The instrument I have invented is operated as follows. Setting the instrument, with two sextants, to measure simultaneously the horizontal angles between the center object and the right and left objects, the index arm of one sextant is moved until the right obiect coincides with the center one below and the other moved until the left object coincides with the center one below. Next switch on an electricity without watching the graduation, and by synchro-motor, twice as large as these angles on two sextants are reproduced to this instrument, which has been made to record the position of the ship. Repeating this means the course will be recorded. The principle of this instrument and the direction for use are illustrated by Fig.1. Its construction is illustrated from Fig.2 to Fig.6.
