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30 THE MarINE REVIEW ~Modern Methods of Lake Navigation for the We now come to the point of find- ing the error of our compasses by the use of the Pelorus. We take a bear- ing of the sun, moon or stars, by our compass. We then look in the book of bearings to find wnat the bearing should be. The principle is the same as finding the error of our compass from a range. We find how our com- pass heads on the range and then find bearing the correct from . the chart AN ORDINARY COMPASS CARD MARKED IN POINTS: ONLY. or lighthouse book. We find how the sun bears by our compass and then we find how it should bear from the book of Azimuths. Bearings of the heavenly bodies are called Azimuths. The instruments for taking these bearings are all simply bearing finders but have different names and each have their special features. They are "The Pelorus," A COMPASS CARD MARKED IN POINTS AND DEGREES, Beginner. BY CAPT. GEORGE TRIMBLE. "The Polaris,' "The Azimuth Attach- ment," "The Alidade," etc. With a knowledge of the working of either one you will easily handle them all. The Pelorus (or Polaris) being the one most generally used we will de- scribe it first. THE PELORUS. Every ship has a Bearing Finder and most of the forward crew know how it is used. The Pelorus is a finely made bearing finder and can be "used for all the purposes of an ordin- ary bearing finder. Its principal use however, is to find the error of a compass by bearings of the heavenly bodies. It has the same dumb com- pass card as is used on a_ bearing finder, the only difference being the degrees marked on the outside edge. = S % Santlllfiig, © PD ° \\ / re a \\\ [! Wy, 6° ie, N a 6° 0% 5 N ~@ Le 40 ae Se °° comers = ea w E = 90 coal = 100 00 -- ot Sa er, BiG: 9. A PELORUS CARD. On some makes of Pelorus this out- side row of degrees is on a movable ring in order to allow for variation without figuring. Herewith we give a cut of an ordinary compass card, Fig. 7, a compass card marked in points and degrees, Fig. 8, and a pelorus card, Fig. 9. Note the dfference between a com- pass card marked in degrees and a Pelorus card. The compass card is marked 0 at north, 90 at east and back again to 0 at south. The Pe- lorus card is marked 0 at north, 90 at. east and up to 180 at south. Any bearing on the east side of the Pe- lorus card between O and 180 is called east and any bearing on the west side of the card between 0 and 180 is called west. A bearing that showed on a compass as_ southeast would be called 135 east on a Pelorus. Every circle has 360 degrees, If you stood on the deck of a boat and faced the north and then turned slowly toward the east and around to south your eye would have tray- elled over 180 degrees of the horizon, This would be the east half of the horizon. If you now faced the north again and turned to the west and around to south your eye would have travelled over the west part of the circle of the horizon or another 180 degrees. a Now, from where you stand, imagine that you can see the horizon marked off in degrees beginning 0 at _ north and so on, around to 9) at east and to 180 at south. Thus our cut shows every 10 de- grees, Fig. 10. 90 POSITION 1 1}8o BIG« 10. The Pelorus is marked to represent this circle of the horizcn. If (from your position) you see the sun direct- ly over the figure 90 her bearing is 90 east. Or properly "her Azimuth is 90 east." Your Pelorus is simply a dumb card marked to represent a compass but with the circle of degrees on the out- side. You this card 10 7 speaking set pelorus