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exchange of matter with the sun in one and the same 

 direction. 



The action of the Northern Lights upon the needle 

 is strikingly similar to that of thunder and lightning.. 

 Two such different phenomena producing result so much 

 alike must obviously have something in common. When 

 we examine them we detect this common factor in the 

 combustion of oxygen which takes place in both cases. 



In the case of thunderstorm the oxygen falling on the 

 heated surface of azote combusts in fulminating sparks, 

 and the hydrogen flies out into space with prodigious 

 force and subsequently falls to earth in form of rain. 

 In the other case the oxygen in combustion furnishes 

 merely a luminous display, and the hydrogen instead of 

 falling, floats. The phenomena are identical in essence 

 and vary only in their form. 



That thunder and lightning take place owing to com- 

 bustion of oxygen is brought home to us when we no- 

 tice that volcanoes no sooner begin to act than their 

 eruption is at once attended by peals of thunder and 

 flashes of lightning. The reason is simple. The fiery 

 lava combusts a mass of oxygen, and the vegetation 

 around is unable to supply the local vacuum. A baro- 

 metrical minimum or lowering of azote ensues and the 

 atmosphere becomes unduly heated, especially in the 

 upper strata. The barometrical maximums around the 

 volcanic mountain roll down their surplus of azote upon 

 this minimum, and the vapour clouds borne along thither 

 explode in storm on contact with its burning air, 



In the barometrical movements ol azote charged with 

 watery vapours it is impossible not to recognize that 

 actio and reactio of which I spoke before as the reason 

 of nature. 



