288 



SCIENCE OF COMMON THINGS. 



Extent of the aurora. Height of the aurora. Appearance. 



north) but in the southern hemisphere it appears in the 

 south : it seems to originate at or near the poles of the 

 earth, and is consequently seen in its greatest perfection 

 within, the arctic and antarctic circles. 



1S81 What is known concerning the extent of the auroral 



It is not local, but it is seen simultaneously at places 

 widely remote from each other, as in Europe and 

 America. 



1883 What calculations "have been made respecting the height of the 

 aurora f 



The height of the appearances varies from one to two 

 hundred miles / they sometimes appear within the 

 region of the clouds, and very near to the earth. 



1883 Do the auroras appear at any particular seasons and times f 



They appear more frequently in the winter than in 

 the summer, and are only seen at night. 



Fig. 84. 



The accompanying figure represents one of the most beautiful of the 

 auroral phenomena. 



1884 Do they also occur in the day -time f 



The aurora is known to affect the magnetic needle and 



