84 



If the diviation caused by the element alone signifies 

 S in divisions of the scale, we will have 



and 



and 



u'— J = S + S' and J— u" = S— S' 



u' 4-u'' 

 u'— u" = 2 S, ^-tJL _ 2 J = 2 S' 



s = Lj -_^ s , = o_±d_._ 2J 



By every observation with the element in opposite di- 

 rections we receive a value of the current caused by the 

 element and of the eleetric air-current. If this låter has not 

 varied the values 



u' 4- u" 

 u — J and J 



must be eqval. 



At the observations in Sodankylä and Kultala it hap- 

 pened very seldom that they vere equal and the calculated 

 values of the EMF must therefore be regarded as approxi- 

 mative. They are so too by an other cause namely by the 

 EMF generated by the earth-plate and by the points in the 

 air. As the last mentioned forces are very small, the pro- 

 bable errors are of subordinate account, especially if we aim 

 principally at the variations. 



The following researche shows that these conclusions 

 are very probable. 



As the two apparatus P n and Pi on the mountain top, 

 of which P n was 10 m higher than Pi, were connected with 

 the galvanometer so that the current from Pn passed through 

 the galvanometer to Pi, we had a deviation Pn — Pi. 



