fig1 extends across the magnetically tight joints between the upper end of the magnet and the undersides of the right and left hand ends of the upper pole 20 through the body of the pole and thence down through the left and right hand pole extensions 34 fig2 across the two air gaps above and below the ends of the armature 62 and thence downwardly through the extensions 36 of the lower pole 22 and back into the body of the magnet 58 as shown in fig3 the armature 62 is of an elongated oval shape and bridges the gap between the left and right hand coil assemblies as viewed in fig2 and 3 it is preferably made of relatively soft very low hysteretic material such as one half nickel and one half iron as most clearly appears in the subassembly shown in fig4 and 5 the previously mentioned adapter 70 is of downwardly presenting bridgelike form the lower ends of the laterally spaced arms 72 rest upon and are suitably secured preferably but not necessarily by gluing to the laterally extending legs 62a and 62b of the armature 62 the elevated central portion 74 of the adapter 70 is thickened and fig3 is secured by longitudinally spaced studs 76 to the enlarged head 78 of the flexure tube 80 the adapter 7 does not require as low a hysteresis effect as does the armature 62 and consequently it is preferably formed from an alloy of aluminum or the like having good surface characteristics and also able to provide a more stable pivot point for the drive arm than could be provided by the relatively soft material from which the armature is made below the flexure tube a counterweight 89 is.