EXPLORATION BY AIRPLANE 405 



In the event of a forced landing, or if the machine had been landed 

 and used as temporary base, even if the pack were drifting it could 

 remain in touch with the rest of the expedition, and a rescue effected 

 if necessary. It has been definitely demonstrated that short-wave 

 communication can be maintained throughout the year from the 

 Arctic to latitudes as far south as the equator, and, once sufficient 

 Arctic wireless stations are established, it will be possible to use radio 

 directional apparatus and to receive weather reports that would make 

 Arctic travel as safe as elsewhere. 



Air Navigation in the Polar Regions^ 



The instruments required for aerial navigation in high latitudes 

 are the same as those used for aerial navigation in other latitudes, but 

 in high latitudes additional advantage may be gained by using the 

 sun compass and quick methods of computation not practicable in 

 low latitudes. The sun compass Is virtually a twenty-four-hour 

 clock used as a sun dial on which the hour hand is the shadow pin. It 

 is useful in cross-latitude flying, but it is of the greatest advantage 

 when the track follows a meridian. Stereographic circumpolar charts, 

 prepared curves, and a revised Sumner method of determining position 

 facilitate aerial navigation in the Polar Regions. 



Except for the great changes in magnetic declination, aerial 

 navigation over the Arctic ice offers less difficulty than in any other 

 part of the globe. Corrections for drift and ground speed depend on 

 altitude, air speed, and time passed in reaching an observation point. 

 A navigator, when flying over some kinds of low terrane and over the 

 ocean, may not be able to find points on which to observe and, when 

 flying over mountainous or hilly tracts, may not know the exact 

 height above sea level of the point observed. (The altimeter carried 

 in the airplane registers only the altitude of the observer above sea 

 level.) On the Arctic ice there are numerous points on which to fix 

 for observation, and these points are known to be at or near sea level. 

 Correct altimeter reading applied to the drift indicator gives the 

 necessary base line for the computation of wind drift and ground 

 speed. The drift and ground speed in low latitudes is generally 

 determined through a series of observations by trial and error, whereas, 

 if three elements of the problem, correct air speed, height, and time of 

 travel, are known — as they might be when flying over the Arctic 

 ice — it is possible by means of instruments now available to work out 

 rapidly the correct ground speed, wind velocity, and direction and so 

 determine the necessary compass correction for any given course. 



The functioning of the magnetic compass in high latitudes depends 

 greatly on the longitude of the area visited. If the area is near the 



1 On this topic see also Mr. O. M. Miller's paper below. — Edit. Note. 



