EXPLORATION BY AIRPLANE 403 



the various materials from which skis may be made. For extremely 

 low temperatures, on hard, wind-driven, granular snow, which acts 

 more or less like hard, dry sand, skis shod with soft metal such as fine 

 brass or duralumin or bottomed with soft wood offer little resistance. 

 For soft, dry snow and very wet snow, the treatment of the wood 

 surfaces with a mixture of Stockholm tar, resin, and tallow ironed into 

 the wood with a hot iron or burned in with a blowtorch gives a very 

 good result. For damp snow, metal surfaces are unsuitable. Probably, 

 for all-round service, a duralumin ski would give the best results, but 

 unless metal skis are of a most expensive design they lack the resiliency 

 and consequent factor of safety offered in a supple ski made of hickory 

 or some other form of hard wood. 



Ski surface area to be used is another consideration that will 

 depend on conditions to be met, and, because the conditions during 

 late winter and spring in the Arctic change rapidly, it is best to adopt 

 a ski of a surface area and material suitable for general conditions. 



The shape of the ski bottom is important. The writer found that 

 a ski 9 inches wide, 9 feet long — of which one foot is turned up in 

 front and 3 inches are curved at the back — with the bottom hollowed 

 by a longitudinal curved groove 6 inches wide and }i inch deep, leaving 

 on each side, a fiat runner i^ inches wide, proved most satisfactory 

 in the Arctic when carrying a plane the total load of which ranged 

 from 2000 to 4750 pounds over a variety of surfaces. The skis used 

 were made of second-growth hickory, treated with the mixture men- 

 tioned. The greatest thickness of the skis was 2 inches, and they were 

 tapered to ^4 inch at the ends. Metal standards were used to fit them 

 to the axles, and the axles were set above the ski at a point fixed by a 

 ratio of 5 to 3, the longer section being toward the front of the machine. 



Snow-surface conditions do not occur in such variety in the 

 Antarctic as in the Arctic, owing in part to a lesser range of seasonal 

 temperature. In the Antarctic wheels would probably not be suitable, 

 but skis could be used all the year round. For coastal exploration 

 in the Antarctic and summer flying in the Arctic flying boats or ma- 

 chines fitted with pontoons may be used, but the use of any type of 

 machine built for alighting only on water is hazardous both in the 

 Arctic and Antarctic. 



Landing Conditions 



Even in water that may appear from a boat's deck to be entirely 

 free from ice there may be small lumps of ice almost submerged and 

 difficult to see from the air when fiying at high speed. A blow from 

 one of these "growlers" might wreck the machine. Another con- 

 sideration is that the polar sea ice is, in summer, nearly always in 

 motion and that the areas of open water change shape and size con- 

 tinually. An area that afforded a good landing place might in a few 



