1. AN ELECTRIC CURRENT TRANSFER DEVICE COMPRISING: AN ELECTRICALLY-CONDUCTING STRUCTURE HAVING A FIRST CONTACT FACE; A UNITARY, SOLID, ELECTRICALLY-CONDUCTING BRUSH OF ARCUATE SHAPE HAVING A UNIFORM CROSS-SECTION ALONG THE LENGTH OF THE ARC AND A SECOND CONTACT FACE AT ONE END OF SAID ARCUATE BRUSH; A HINGED SUPPORTING ARM, SAID ARCUATE BRUSH BEING MOUNTED AT ITS OTHER END AN SAID ARM WITH CENTER OF CURVATURE OF THE ARCUATE BRUSH COINCIDENT WITH THE HINGE AXIS; AND BIASING MEANS EXERTING A TORQUE ON SAID ARM TO BIAS SAID CONTACT FACES INTO ENGAGEMENT, SAID CONTACT FACES LYING IN RADIAL PLANES PASSING THROUGH SAID HINGE AXIS.