262 THE DIRECT-CURRENT MOTOR CIT. XII 



of opposite sign to that on the other side, and that it is 

 independent of the position of the wire under the pole. 



We can now pass from the case of a single wire to that 

 of a number of wires placed side by side on the surface of 

 the armature. Consider first the wire at the point A- lying 

 under the pole A. Suppose that the dynamo is acting as a 

 motor and that the current in this wire is coming towards 

 us, the intensity of magnetisation at each point along the 

 gap due to the current i flowing in the wire at A- is then 

 given by Equation 112. Now all the conductors lying to 

 the right of h will produce an effect at h of the same sign 

 and amount as the wire at If. Hence if there are Sj con- 

 ductors between h and the right-hand pole-tip, the intensity 

 of magnetisation produced at k by all these conductors will 

 be given by 



where i is the current in each conductor. 



The conductors lying to the left of h, between h and 

 the left-hand pole-tip, will produce an effect at h of 

 opposite sign to those on the right of 7t, the intensity being 

 given by simply changing s, to s 2 in Equation 112, where 

 s 2 is the number of conductors lying between h and the 

 left-hand pole-tip. The resultant intensity at h is the 

 difference between these two intensities, and may be 

 written 



where s 3 is the number of conductors lying between h and 

 the centre of the pole. 



This equation shows that the intensity due to the 



