260 



Mr Macdonald, On the Self-induction [Nov. 23, 



Solving these for H, H Q and H' and determining L from them, 

 we obtain 



+ ~ 



When fi = fi we have the case of the a conductor iron, the other 

 being copper, and then 



aa 



the repulsive force between the conductors being 



fi - fi a' 2 



*efvi- 



fi + fi. b' 2 — a' 



Taking the case of conductors of equal section, the following 

 table shews how the variable part of the coefficient of induction 

 varies with their distance apart. 



The first column gives the distances between the axes of the 

 conductors, the second the values of half the variable term in 

 Maxwell's formula, the third half the term which has to be 

 added to it, the fourth the increase per cent, of the variable part 

 due to the term neglected by Maxwell, the fifth and sixth the 

 values of the variable parts in both cases ; /a being taken unity 

 and yu. = 100. The table shews that the term neglected is con- 

 siderable when the conductors are close to one another, and 

 decreases rapidly at first as b increases, afterwards slowly. 



