If the corrosion is electrochemical, it may be concluded from this work that: 1. In order that protection may be complete, the potential of the cathode areas must be polarized to a potential equal to or more anodic than the open circuit potential of the anodes. 2. In order that protection may be complete in solutions where the cathodic polarization is large compared with the resistance drop, the cathode must be polarized to the open circuit potential of the anodes. 3. In order that protection may be complete in solutions where the cathodic polarization is small compared with the resistance drop, the cathode must be polarized to a potential more anodic than the open circuit potential of the anodes. 4. The current required for complete protection will depend upon the current required to polarize the cathode to a potential equal to or more anodic than the open circuit potential of the anode. 5. The current required for complete protection will depend upon the position of the auxiliary anode relative to the position of the local anodes and cathodes. 6. The less the potential drop between the auxiliary anode and the local cathodes, the less the current required. 7. Special attack or inhibition may be produced by the products of electrolysis resulting from the application of cathodic current. 8. Special attack on surfaces which are made cathodic may be beneficial if the type of attack is also altered.