CHAP, iv.] ELECTRICITY AND MAGNETISM. 



263 



auroral arches and streamers with respect to the 

 magnetic meridian, directly suggest an electric origin 

 for the light, a conjecture which is confirmed by the 

 many analogies found between auroral phenomena and 





Fig. 112. 



those of discharge in rarefied air (Arts. 292 and 294). 

 Yet the presence of an aurora does not, at least in our 

 latitudes, affect the electrical conditions of the lower 

 regions of the atmosphere. On September i, 1859, a 

 severe magnetic storm occurred, and aurorae were 

 observed almost all over the globe ; at the same time 

 a remarkable outburst of energy took place in the 

 photosphere of the sun ; but no simultaneous develop- 

 ment of atmospheric electricity was recorded. Auroras 

 appear in greater frequency in periods of about 1 1 J 



