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32 Now remember this, if we find that netic bearing of this range is then our compasses have a deviation of a certain amount while heading in a certain direction don't think that they will have the same deviation when heading-in any direction. Some com- passes are perfect when heading in a northerly direction but show a big error when heading south or east or west. The error should be found for every point of the compass. Four different deviation cards should be made for use on the river ranges. One card should be headed "Going north without cargo.' Another should head "Going 'north loaded." The other two should head "Going south loaded" and "Going south without cargo." The reason that one card won't do for all corrections is that a boats compass acts differently when light and loaded and also acts differently when going north or south. On each card is written the name of each river range. The correct mag- ' 1 | | OUR COMPASS HEADS LIKE THIS, FIG, Tac MARINE REVIEW given and then your ship's heading on that range is given. Thus: (as shown above) you would have to steer N by W by your steamer's compass. More about compasses and _ their eae STEAMER ROOSEVELT DEV/ATION CARD Bound up, Loaded NATE OF RANGE CORRECT MAGNETIC STEAMERS CO/VFASS | DEV/AT/ION Walden nnge (ain) 'Gh. Doss Under the head of "Deviation cards for river ranges" you will find com- iplete cards for all the river ranges. These can be pasted to a piece of cardboard and taken to the bridge each trip through the rivevs. You can see at a glance then whether they have shifted their deviation s'nce the previous trip. The advantage of using deviation "cards, can be. seen: at .a glance. If you wanted to make a course on the lake of N by W % W Nn Ww E | K > 9 yy 3. BUT IT SHOULD HEAD LIKE THIS, AN hy WW GHE be ya thee nie ei. eee fickleness is given under the head of "Expert knowledge of the compass.", A Ric, 4. An outline of the work is intended here to prepare for finding the error by the heavenly bodies. How are we to find the- error of our compasses when we are where there are no ranges or piers to get