406 POLAR PROBLEMS 



magnetic pole the problem of navigation by means of the magnetic 

 compass is difficult, not only because of rapid changes in declination 

 but also on account of the sluggishness of the horizontal needle with 

 which the ordinary compass is fitted. Compasses for high-latitude work 

 should have exceptionally large clearances for vertical movement. 

 Special care must be taken to eliminate deviation. A compass that 

 somewhat eliminates that difficulty is the earth inductor compass, 

 which may be installed in the plane far from the interference of 

 engine ignition and which can be remotely controlled by the pilot or 

 navigator. The earth inductor compass dial can be set at any con- 

 venient point and not necessarily near the directional mechanism. 

 Like other compasses it was found in high latitudes to be less positive 

 in its action and therefore less reliable. 



Astronomical observations and the use of prepared charts and 

 tables are a means of checking position, but position-finding by 

 means of bubble-sextant observations taken from the cabin of a fast- 

 moving airplane, when the sun is low in the heavens and refraction 

 at high elevations in high latitudes an unknown factor, is likely to 

 be inaccurate. 



The Arctic especially offers many aids for piloting, i. e. keeping 

 a course by the observation of surface conditions. The ability to 

 "line up" on points of ice, careful observation of the direction of 

 snowdrifts, the lighting on the ice pack during periods of sunshine, 

 the azimuth of the sun, visible for twenty-four hours a day during 

 summer, the direction of open leads of water or the surface condition 

 of recently frozen leads, which give an indication of past, present, and 

 future air currents (the ice movement is often an indication of wind 

 direction long before and long after the actual wind has passed a 

 given point) — are all aids to a navigator in the Arctic that may not be 

 found in lower latitudes. 



Even flying through fog conditions over the Arctic pack ice offers 

 less danger than flying in fog in other latitudes, as was pointed out 

 before. There are few obstructions as high as a hundred feet on the 

 Arctic sea ice, and this enables the pilot to fly low at a constant, known 

 height. With a visibility of less than 300 feet, we discovered from 

 actual experience in 1926 that it was possible to get some idea of the 

 rough ice horizon and keep our airplane on an even keel. The pilot 

 had, under those circumstances, little to occupy his attention except 

 the direction of flight. In fog over the sea ice there is little turbulence 

 in the air, and low flying is comparatively safe. 



Observations To Be Made 



It is as easy to carry out a detailed survey by means of aerial 

 photography in the Polar Regions as it is in other latitudes. Prolonged 



