ATMOSPHERIC ELECTRICITY IN HIGH LATITUDES. 81 



high latitude by some writers, who base their general conclusions on a few observations 

 made by ELSTEE.* 



lonization. At the time of writing no similar series of observations made with 

 EBERT'S apparatus have been published, so it is impossible to compare the ionization 

 in high latitudes with those in lower. But judging from my own experience, as with 

 the dissipation there is no change in the ionization which cannot be explained by the 

 meteorological conditions. There is certainly no abnormal ionization nor abnormal 

 unipolarity, both the ratios q and r being in excellent agreement with those found in 

 Germany. 



The yearly course of the ionization is of great interest and of much importance. 

 What causes the yearly variation is not at first obvious. The ionization of the 

 air at any moment is determined by two factors : firstly, the rate at which ions 

 are produced in the air, and secondly, by the rate at which they re-combine.t The 

 yearly variation of the ionization must be caused by variation in either one or both 

 of these factors. We do not yet know what the ionizing influences at work in the air 

 are ; but possible ones are radio-emanation, the sun's light, and temperature. But 

 none of these undergo a yearly change corresponding to that of the ionization. It 

 will be shown later that the yearly course of the radio-active emanation in the air is 

 exactly opposite to that of the ionization. The sun's light and the temperature both 

 have a yearly course in some agreement with that of the ionization, but the maxima 

 and minima do not agree : the maximum and minimum of the ionization fall two 

 months behind those of the sun's light and one month behind those of the temperature. 

 We should then rather expect to find a cause for the variation by assuming a constant 

 ionizing factor and looking for a change in the conditions which affect the 

 re-combination of the ions. One of the first things which ELSTER and GEITEL found 

 when working at the ionization of the air was that the dissipation depends to a great 

 extent on the clearness of the air. This factor in itself is capable of accounting for 

 the yearly course of the ionization at Karasjok. 



All who have travelled in Arctic regions know the peculiar haze which fills the air 

 when the temperature falls very low and gives the " cold " aspect to Arctic scenes. 

 Such a haze, which is not a mist or fog, was frequent during the winter at Karasjok. 

 On the other hand, at the end of the summer the air reached a degree of 

 transparency which I have never seen equalled in any other place. On going into 

 the open air one was often struck with the great transparency of the atmosphere, 

 giving sometimes the impression that the air between one and distant objects had 

 been entirely removed. That it is the transparency of the air rather than the 

 temperature which determines the ionization could often be seen from individual 

 observation. On June 16 the temperature rose to the abnormal value of 247 C., 

 the air being exceedingly hazy and oppressive ; the ionization was only '18, the mean 



* 'Phys. Zeit.,' 2, p. 113, 1900. 



t SCHUSTER, 'Proc. Man. Lit. and Phil. Soc.,' vol. 48, Part II., p. 1, 1904. 

 VOL. CCV. A. M 



