42 SPECIAL RESULTS IN THE URANOLOGICAL 



furnish a means of determining the superior limit of the 

 density ascribable to the ether, if we assume it to resemble 

 terrestrial gaseous fluids in its powers of refraction. 



Connected with the question of the existence of a space- 

 filling ethereal fluid, is the one proposed with so much ani- 

 mation by Wollaston, ( 87 ) of the limit of the atmosphere, 

 a limit which must exist at the height where the specific 

 elasticity of the air and the attraction of gravitation are in 

 equilibrium. Faraday's ingeniously devised experiments 

 upon the limit of an atmosphere of mercury, on the height 

 which vapour of mercury tested by amalgamation with 

 gold-leaf scarcely appears to reach in air, have given 

 increased weight to the hypothesis of a definite surface of 

 the atmosphere, " similar to the surface of the sea." May 

 gaseous substances from space mix with our atmosphere and 

 produce meteorological changes ? Newton ( 88 ) has touched 

 this question, leaning to the affirmative side. If shooting 

 stars and meteoric stones are regarded as planetary asteroids, 

 we may well hazard the conjecture that, with the streams of 

 myriads of shooting stars which traversed the sky in the 

 month of November, ( 8 9) in the years 1799, 1833, and 

 1834, and when Auroras were observed at the same time, 

 the atmosphere received from space something which was 

 extraneous to itself, and which might excite electro-magnetic 

 processes. 



