7 and secondary disks 20 then by a first yoke 24 then primary disks 7 u2032 and secondary disks 20 u2032 then a further first yoke 24 u2033 primary disks 7 u2033 and secondary disks 20 u2033 and finally the right hand second yoke 27 u2032 fig3 shows the embodiment of fig1 with the primary shaft however being omitted and only the secondary disks 20 of the secondary part being able to be recognized the field lines 28 29 are again drawn in symbolic manner the cones which they pass through are their direction arrows the second embodiment of fig4 differs from fig1 by the different arrangement of parts of the first yoke and of the corresponding coil which is better expressed in the axonometric view of fig5 the reference numerals are those of fig1 but increased by 100 here the first yoke 124 here comprises a plurality of winding cores 124 a outer row and 124 b inner row which are distributed in two rows over the periphery with a zone of low magnetic permeability 124 c therebetween each of the winding cores is wound around individually here and is thus encompassed by its own magnetic coil whose winding axis is parallel to the axis of rotation 9 and is in the winding cores 124 a and 124 b the winding axes in fig6 lie in the field lines 128 129 drawn in tube like manner it is important that the magnetic coils 125 a outer row and 125 b inner row are oppositely poled in fig6 only the winding cores can be seen the magnetic coils themselves have been omitted all.