ATMOSPHERIC ELECTRICITY IN HIGH LATITUDES. 



71 



smallness during the Bummer and autumn its position is not then well fixed. The 

 ratio of the amplitude of the second period to the first is : winter '40, spring - 65, 

 summer '56, autumn '83, whole year '59. This shows no regular variation ; the large 

 value for the autumn is due to the strengthening of the second period by the 

 formation of mists over the river about the times of sunrise and sunset, which mists 

 always give rise to high potential gradients. 



The hourly values of the potential gradient corresponding to the five curves are 

 given in the following table : 



TABLE IV. Daily Course of the Potential Gradient. 



Dissipation. As I had no self- registering instrument to record the dissipation and 

 ionization, it is impossible to work out the daily course of these two as has been done 

 for the potential gradient. Nevertheless, some idea of the course can be obtained by 

 comparing the results according to the different times of observing. In Table V. the 

 mean results from the morning, midday and evening observations are shown for each 

 three months and then for the whole year. 



