446 



POLAR PROBLEMS 



of checking his position. Now, because it is essential that the navi- 

 gator determine his position practically on the instant while flying, 

 most astronomical methods are valueless. However, there is one that 

 can be employed which is simpler to use in the polar regions than in 

 other parts of the world provided one knows Greenwich time, and 

 there should be no difficulty about this in these days of wireless time 

 signals and good chronometers, especially as it is not necessary to 

 know the time with absolute precision. 



The particular astronomical method in question has been employed 

 by all the navigators in the recent flights in the polar regions for check- 

 ing their dead-reckoning positions. It is sometimes described as the 

 Marc St. Hilaire method with the pole as the assumed position,^ 

 but this is hardly an adequate description. 



By observing an altitude of the sun or other celestial body it is 

 possible to define one's position as being somewhere on a circle of 

 poi^£ equal altitude which has as its cen- 



ter the point on the earth's surface 

 at which the celestial body was in 

 the zenith or directly overhead at 

 the moment oi observation. Ihe 

 radius of this circle is equal to the 

 zenith distance. When one is in 

 the polar regions it is very easy, and 

 requires no computation, to plot 

 this position line on the chart, because the meridian which the heavenly 

 body was crossing at the time of the observation is known and the dis- 

 tance from the pole along this reference meridian to the point where 

 the circle of equal altitude cuts it is equal to the difference (h — <i in 

 Fig. i) between the sun or star's declination (d) and the observed alti- 

 tude (h). If the altitude is larger than the declination, this point is 

 between the pole and the sun or star ; but, if the opposite is the case, 

 then the point lies on the opposite side of the pole to the latter. The 



2 The development of this method is interesting. As long ago as 1892 Professor Hans Geelmuyden 

 of Christiania suggested (Stedbestemmelse paa hole Bredder, Videnskahs-Selskahel i Chrisliania 

 Forhandlinger, 1892, No. i) a graphic method of plotting position lines on a stereographic projection 

 suitable for use in the polar regions, and undoubtedly Nansen used such a method on the voyage of 

 the Fram. However, the particular simplification described in this paper was first suggested — at any 

 rate in the English language — by Professor Harry Fielding Reid in a paper entitled "How Could an 

 Explorer Find the Pole?" {Popular Sci. Monthly, Vol. 76, 1910, pp. 89-97)- Later Mr. A. R. Hinks in 

 a paper entitled "Notes on Determination of Position Near the Poles" {Geogr. Journ., Vol. 35, 1910, 

 pp. 299-312) suggested the same simplification as a method of checking up on explorers' observations. 

 According to Lieutenant Hjalmar Riiser Larsen (Roald Amundsen, Lincoln Ellsworth, and others: 

 Our Polar Flight, New York, 1925, p. 173), H. V. Sverdrup used the method on the voyages of the 

 Maud, and it would appear that Sverdrup was the first to use it in the field whilst Larsen was the 

 first to use it in an airplane flight, namely the first Amundsen-Ellsworth flight in May, 1925. Since 

 then several descriptions of the method have appeared, e. g. G. W. Littlehales: Finding Geographical 

 Position in the Region of the North Pole, U. S. Naval Inst. Proc, Vol. Si. 1925, pp. 1339-1342; H. 

 Coldewey: Ortsbestimmung im Polargebiet, Annal. der Hydrogr. und Marit. Meteorol., Vol. 53, 1925, 

 pp. 345-347; A. R. Hinks: Second Note on Determination of Position near the Poles, Geogr. Journ., 

 Vol. 68, 1926, pp. 58-62. 



Fig. I. 



