6o POLAR PROBLEMS 



Though the Maud, during her drift in the Arctic ice from 1922 to 

 1925, was generally not far from the belt of maximum auroral fre- 

 quency, Dr. Sverdrup found no relation between the potential gradient 

 of atmospheric electricity and the aurora. Regarding this matter 

 the results from various polar expeditions and observers are again 

 conflicting. Unfortunately the Maud did not possess the necessary 

 instrumental equipment for measurements of the electric conduc- 

 tivity of the atmosphere, which would have been of interest also in 

 connection with the question of the relationship between the aurora, 

 atmospheric electricity, and radio reception. 



The determination, by the Stormer parallactic photographic 

 method, of the depth of penetration into the atmosphere of polar- 

 light beams in regions near the magnetic poles is an important matter. 

 The many thousand observations made by Stormer, Krogness, and 

 Vegard, in northern Norway have shown that for that region the au- 

 roral beams do not come closer to the earth's surface than about 90-100 

 kilometers. Yet, according to accounts of some explorers, the beams 

 in the Arctic regions have penetrated at times much deeper into the 

 atmosphere. The Department of Terrestrial Magrtetism supplied the 

 MacMillan Baffin Island expedition of 1921-1922 with the necessary 

 equipment and instructions for investigations of the height of the 

 aurora, at the winter quarters of the expedition on the southwest coast 

 of Baffin Island ; unfortunately, owing to various causes, the expedition 

 was unable to take the desired parallactic photographs. Here, then, 

 remains open an important field of investigation, both in the Arctic 

 and the Antarctic. 



The great importance of special radio experiments in the polar 

 regions for elucidating the connection between the aurora and the 

 properties of the conducting layer deserves special mention. Experi- 

 ments made at the laboratory of the Department of Terrestrial Mag- 

 netism at Washington by G. Breit and M. A. Tuve^^ in 1925 showed 

 that it is possible to measure approximately the height of the con- 

 ducting layer by radio signals. Dr. Breit considers it very desirable 

 that the heights of the aurora and of the conducting layer be ascer- 

 tained simultaneously at the same station. 



Among other important investigations regarding polar lights might 

 be mentioned, for example, those having a bearing on the experiments 

 by Vegard of Oslo and McLennan of Toronto with a view to the 

 explanation of the spectrum of the aurora. 



Atmospheric Electricity 



Under the preceding head some suggestions have already been 

 given regarding investigations in atmospheric electricity open to polar 



" Physical Rev., Vol. 28, Menasha, Wis., 1926, pp. 554-575. 



