102 



will not be the same as at the end of the foregoing tum, but it 

 has been delayed, that is to say has undergone an infinitly 

 little clisplacement, retrograde against the rotation of the Earth. 

 In the daily movement of the direction of the magnetisme 

 we shall find the cause of the daily variation; in the daily 

 infinite little displacement we shall find the cause of the 

 yearly and secular variations, for this direction must rotate 

 in retrograde sense around the poles of the Earth. The 

 time for this rotation ought to be about 600 years. 



On the surface of the soil electricity is always produ- 

 ced by several causes, about which men of science have 

 many different opinions. Our conception is that the prin- 

 cipal cause lies in the evaporation, always active on the 

 Earths surface. Hereby the unipolar induction produced by 

 the Earth as a rotating magnet, exercises its effect in crea- 

 ting a force which drives the positive electricity up in the 

 atmosphere and thus makes every evaporated particle to» a 

 bearer of electricity. 



The air at ordinary pressure is an insulator, but 

 rareiied air is a relatively good conductor of it. The Earth 

 is surrounded by a spacé of rarefied air, which forms with 

 the earth-surface, being a good conductor, a condensator 

 with a layer of insulating air between them. The space in 

 which the air is rarefied is very väst, but we can imagine 

 it to be made up by a much smaller space between two 

 concentric surfaces O' N' E' S' and the other within it; we 

 must only ascribe to it the same properties in electric way, 

 which the väst space possesses. We will call it the air- 

 conductor. 



As the temperature on the earth-surface varies very 

 much, this air-conductor, which in the equator-regions is 

 on a hight of about 40 km, (supposed to be in a space 

 with the pressure of about 5 ram ), will descend by and by 

 in the measure as we approche the poles, in consequence 

 of the fall of the temperature. The more the temperature 

 falls the nearer to the surface of the Earth the air-conduc- 

 tor will come. 



