345 



near that extreme limit where the centrifugal 

 force is balanced by gravity, there exists at 

 regular periods a particular disposition for the 

 production of bolides, falling stars, and the 

 Aurora Borealis *. Does the periodicalness of 

 this great phenomenon depend upon the state 

 of the atmosphere? or upon something which 

 this atmosphere receives from without, while 

 the Earth advances in the ecliptic ? Of all this 

 we are still as ignorant as men were in the days 

 of Anaxagoras. 



With respect to the falling stars themselves, 

 it appears to me from my own experience, that 

 they are more frequent in the equinoctial re- 

 gions than in the temperate zone; more fre- 

 quent over the continents, and near certain 

 coasts, than in the middle of the ocean. Do 

 the radiation of the surface of the globe, and 

 the electric charge of the lower regions of the 

 atmosphere, which varies according to the na- 

 ture of the soil, and the positions of the conti- 

 nents and seas, exert their influence as far as 

 those heights, where eternal winter reigns ? The 



* Hitter, on the periods of nine or ten years (1788, 1798, 

 1807,) in Gilbert's Annals, Vol. xv, p. 2L2 ; Vol. xvi, p. 224. 

 He makes a distinction, like several other natural philoso- 

 phers, between the bolides mingled with falling stars and 

 those luminous meteors, which, enveloped in vapours and 

 smoke, explode with great noise, and let fall (mostly in the 

 day-time) aerolites. These latter certainly do not belong to 

 our atmosphere. 



