ELECTRICITY. 



493 



Descriptive 

 Electricity. 



Heights of 

 the aurora 



borealis. 



TABLE sheu-ing the heights of the Aurora Borealis. 



Descriptive 

 Electricity. 



Heights of 

 the aurora 

 borealis. 



Tire tall'. 



The other luminous meteors, which have been consi- 

 dered as electrical, are fire balls or globes of fire, shoot- 

 ing xtarg, and the fire of St Elm. 



Fire balls are less frequent than other meteors, and 

 generally consist of large globes of fire advancing with 

 a progressive motion. The fire boll which appeared on 



the 17th July 1771, was seen by a great number of phi- Fi* teik. 

 losophcrs in various parts of England and France. It 

 appeared to be aliout a foot in diameter, or larger than 

 the full moon, and had a progressive motion from north- 

 west to south-east. The light, which was very intense, 

 lasted only a few seconds, and two minutes after it had 



