It will be seen that the coil consists of two 'active' conductors which have been designated AB and CD. these are connected in series by the connection BC which, together with the front connections to the slip-rings, plays no part in the generation of E.M.F but merely serves as a means of carrying current to the external circuit. The load resistance of the external circuit has been shown as concentrated in R and is connected to the terminals X, Y of the machine.