COMMUTATOR. HAND ELECTRODES. 



187 



The leading in binding screws are attached to mercury cups, into 

 which the middle arms of the rocker are placed. For the purpose 

 of reversing, the cross wires are used, and the leading out connections 

 are attached to the binding screws, and so to the cups on one side 

 only. When the arms of the rocker dip into these, the positive pole 

 remains on the same side ; when the rocker is reversed the other 

 leading out wire becomes positive. 



DEFLECTER 



FIG. 23. Diagram of Pohl's commutator. The rocker R is shown in position 

 for reversal of the current in the left-hand figure. 



To use the Pohl as a current deflecter the cross wires are removed, 

 the connections of the two alternative circuits are made with opposite 

 pairs of cups, and the rocker changes the path when it is moved 

 .from one set to the other. 



FIG. 24. Hand electrodes. 



Hand electrodes : Two stout copper wires are passed through 

 glass tubes for insulation and rigidity. The ends of the latter are 

 sealed with electric cement ; the tubes are tied together and their 

 ends are covered with marine glue, the free ends of the wire are 

 shaped conveniently. The other ends are soldered to flexible wires 

 which terminate in tags that will fit either screw-down or perforated 

 .terminals. 



