530 



importance, 1 nit such observations would at least have shown if there were anything alnmniiul in the sign 

 of the potential, or even if there were anything extraordinary in its magnitude (hiring an aurora, or if 

 there were fluctuations corresponding to changes in the appearance of the aurora. In all cases, however, 

 the sign of the potential was apparently normal, and there was nothing remarkable in the values of the 

 readings. 



It is not easy to decide definitely from the ordinary series of potential readings whether auroras have 

 any influence on the electrical field. It is only for about half the year that auroras could be observed, 

 and it is just during this half of the year, >., the winter months, that the observations of potential were 

 fewest. Again, while the conditions were suitable for seeing them, 'auroras were of practically daily 

 occurrence, so that possibly the potential, as it would be outside the influence of auroral disturbances, was 

 never observed. 



Perhaps all that can be done is to pick out the days on which auroras of abnormal brightness, extent, 

 or duration occurred, and see if the potential on such days differs from the mean for the month. In the 

 following table are given the days on which specially conspicuous auroras occurred, and the results of 

 such observations of potential as were made on these days, the mean of the undisturbed potential readings 

 for the month being also given. 



There is some indication of disturbance of the electrical field by these specially intense auroras, low 

 values being apparently liable to occur. There is one case, April 22, 1903, of an exceptionally high value; 

 this was not accompanied by drifting snow or other abnormal conditions. 



