103 



The quantities of electricity, which are carried up by 

 the watery vapours on this air-conductor, will hereby, go- 

 verned by tbe ordinary laws, arrange themselves in this 

 way that a greater density of electricity will occur in the 

 polar-regions and hence the attracting force between the 

 negative electricity on the earth-surface and the positive on 

 the air-conductor will increase by and by. This force can 

 under certain circumstances, not unusual, attain a value 

 40 % greater than in the equator- regions. 



As the force has increased to a greatness to over- 

 come the insulating power of the air-layer between the air- 

 conductor and the earth-surface, an électric air-current be- 

 gins to flow between them. This current occuring princi- 

 pally in the maximum belt shows only that the force has 

 already in this latitude attained the intensity necessary to 

 overcome the insulating power of the lower air-layers. 



The earth-magnetisme exercises hereby a great in- 

 fluence, which seems by the situation of the maximum belt, 

 lying around the magnetic pole. The unipolar induction, 

 which in the equator-regions cooperates with the evapora- 

 tion to produce electricity in the atmosphere, looses by app- 

 roching the poles by and by its signification, because its 

 direction, being always normal against the total magnetic 

 force, after having been vertical near the equator will be 

 horizontal in the magnetic poles. Its resistance against the 

 électric air-current diminishes by and by and is null in the 

 magnetic poles. It is very little already in the maximum 

 belt and the électric air-currents flow there nearly without 

 hindrance in the direction of the total magnetic force and 

 therefore we see north-light beams take principally this di- 

 rection. 



The électric quantities, which flow down in the maxi- 

 mum belt, produce earth-currents and it is of course natu- 

 ral that this belt shall be connected with an other belt, in 

 which the earth-currents in number and intensity are in 

 maximum, as we have seen in the foregoing pages. 



