AIR NAVIGATION 455 



in this direction. Consequently most navigators prefer in the absence 

 of fog to steer a straight course by means of ranging in on natural 

 objects or by taking back sights on smoke bombs dropped in the course 

 of the flight. The first of these methods is quite practical over an 

 ice field, as has been shown by Commander Byrd and Captain Wilkins. 



Suitable Map Projection on Which to Plot Course 



For purposes of general convenience the recording of the progress 

 of a flight should all be done graphically on a chart ; and consequently 

 it is important to consider what projection is most suitable for such 

 charting by the navigator in the polar regions. The Mercator pro- 

 jection, so useful to mariners in that it shows a rhumb line as a straight 

 line, is out of the question because the polar regions cannot be plotted 

 on it. Two projections worth considering are the polar gnomonic and 

 the polar stereographic. The former has the advantage that all great 

 circle lines are shown as straight lines, but scale distortions become 

 very noticeable as the chart extends away from the pole. The polar 

 stereographic chart on the other hand is fairly free from scale distor- 

 tion in the polar regions and shows all great and small circles as circles 

 on the chart, with the exception of meridians, which are straight lines. 

 The second projection, therefore, is of great convenience in plotting 

 astronomical position lines and in scaling distances, while the first is 

 suitable for plotting direction. The ideal solution of the projection 

 problem would be for navigators to carry polar charts on both projec- 

 tions; but exigencies of space and time would probably prevent this, 

 at any rate on an airplane flight. Consequently it seems desirable to 

 determine whether it would be possible to construct a compromise 

 projection of the polar regions in which the errors of both the stereo- 

 graphic and gnomonic projections would be reduced to such an ex- 

 tent that for navigational purposes they could be ignored. 



Need of Ability to Navigate Between Two Points 

 Not on the Same Meridian 



In conclusion it is absolutely necessary to emphasize one aspect 

 of the problem. On the three flights in the neighborhood of the pole — 

 namely the first Amundsen-Ellsworth flight, navigated by the Nor- 

 wegian Lieutenant Hjalmar Riiser-Larsen, Commander Byrd's flight 

 to the north pole, and the flight of the airship Norge — no attempt was 

 made to fly for any sustained period in any direction except due north 

 or south. ^■^ The reason for this is obviously because the objective of 

 each of these flights was to reach the north pole. Without wishing in 



" After the Norge had crossed the pole and lost track of her position owing to fog, her navigator 

 took the first opportunity to take sun sights and plot position lines. As soon as one position line 

 pointed nearly due north and south he followed the meridian indicated until he sighted the Alaskan 

 coast. 



