the track so that the air circulation caused by the movement of the carriages may not be sufficient adequately to cool the primary member of the linear induction motor of course appropriate cooling fins would also be provided fig9 illustrates an alternative construction in which a wand 32 pivoted at one end 33 on a carriage 22 is driven to move through reciprocating angular movement by a link 44 connected to an eccentric pin 45 on a gear wheel 46 carried by a fixed arm 47 secured to the carriage 22 the gear 46 rolls over and meshes with a fixed gear ring 48 carried on the frame of the machine the relative radii of the gear 46 and the fixed gear ring 48 are selected so that the gear 46 makes the same number of rotations about its own axis as there are sections 17 of the primary member as it traverses around the fixed gear ring 48 on movement of the carriage 22 as it rotates around its own axis the gear 46 causes the connecting rod 44 alternately to draw radially inwardly and then push radially outwardly the wand 32 thereby causing this to reciprocate angularly so that the wand tip 32b from which the wire on the carriage 22 is drawn follows.