Page:Electricity (1912) Kapp.djvu/108

104 to the two conductors g and f, between which a difference of potential is to be established or kept up—in our case ink and paper. Within the cylindrical cavity is another pair of insulated segments a and b, connected by an insulating bridge-piece C mounted on a spindle, by which the inner system may be revolved. The knob above mentioned is fixed to the end of this spindle. By twirling the knob rapid rotation of the two inner segments can be produced, and thus a is alternately brought to face A and B at the same times that b is brought to face B and A respectively. The inner segments have each a projecting piece by which a momentary connection is established with fine wire brushes. These are fixed in the position shown d, e, f, g. The brushes d and e are connected by a wire, and the other two brushes are connected as shown with the outer segments.

To explain the action of the replenisher, let us start with the assumption that A has a small positive and B a small negative charge. It is immaterial how small these charges are, since, as will be seen presently, the action is cumulative, so that the merest trace of a charge quickly grows to a quite formidable value. It may be here mentioned that the same principle