80 



ME. GEOKGE C. SIMPSON ON THE 

 TABLE XV. Potential Gradient and Temperature. 



The Aurora and the. Electrical Conditions of the Atmosphere. 



During the whole of my stay in Karasjok I could not detect the slightest effect of 

 the aurora on any of the electrical conditions of the atmosphere, and most careful 

 watching of the needle of the self-registering electrometer did not show any relation 

 between potential gradient and the aurora. On first starting my observations I 

 thought I found, as many other observers have done, an unsteadiness of the potential 

 gradient during an aurora display, but longer experience showed that this unsteadiness 

 had nothing to do with the aurora. In order for an aurora to be visible it must be a 

 clear night, and a clear night is generally accompanied by low temperature and a 

 high potential gradient. The high potential on clear cold nights was always unsteady 

 and varied quite irrespective of the presence or absence of an aurora. When an 

 aurora was visible naturally it often appeared as if a change in the aurora was 

 coincident with a change in the potential gradient, but the attempt to connect 

 changes in the potential gradient with changes in the aurora over any length of time 

 always failed. Other observers have recorded negative potential gradient during an 

 aurora display ; but during the whole winter my self-registering electrometer did not 

 once record any such reversal. 



CONCLUSIONS TO BE DRAWN FROM THE WORK. 



The first and most important conclusion is that the difference in the electrical 

 conditions of the atmosphere between mid-Europe and this northerly station can all 

 be accounted for by the difference in the meteorological condition at the two places. 



Dissipation. For reasons which have been set out above, the actual numbers 

 obtained for the dissipation cannot be compared directly with those of other observers, 

 but one is quite safe in saying that they are of the same order as those obtained 

 further south under the same meteorological conditions. They certainly do not show 

 that great increase in dissipation and unipolarity which has been ascribed to places of 



