83 



A galvanic element (Leclanché or better a normal 

 Daniel) vvith constant EMF of known value L in volt was 

 introduced in the circuit first with its positiv pole towards 

 the point-apparatus and than with its negativ pole towards 

 it. Let us signifiy the deviation read on the scale in the 

 first case u' and in the second u", the deviation for the el. 

 air-current alone (supposed positive or from the atmosphere 

 to the earth) u, the position of equilibre J, the EMF of the 

 el. air-current E and the electric resistance in the whole 

 circuit q, we will have 



L 



k [(u'- J) — (u— J)] = k (u'-u) = — 



L 

 k [(u'-J) — (u"— J)] = k (u— u") = — 



0) 



where k signifies the constant of the galvanometre (in am- 

 pere). Putting 



u— J==S' 



we have 



E 



kS' = — (2) 



o 



and by division of (1) with (2) 



2L 



e = ^—t;S' (3) 



where E is expressed in volt. 



