engageable to both friction wheels 12 16 is the means of coupling knob 18 to shaft 7 the bearing 6 for driven shaft 7 is secured to a carriage 3 which is guided by coacting guide means 105 on the fixed part or base 106 of the mechanical stage so that bearing 6 is displaceable in the plane of the drawing bearing 6 also carries a tubular shaft 10 having a pinion 9 which meshes with a rack 5 that is bolted at 107 to the fixed stage part shaft 10 is driven by a rotary knob 15 via second friction wheel mechanism consisting of a drive side friction wheel 13 fastened to the shaft 14 of knob 15 a pressure roller 19 and a driven side friction wheel 11 on shaft 10 the drive mechanism housing 4 in which the coaxial drive mechanism 13 18 is mounted is also fastened to carriage 3 accordingly upon rotation of knob 15 carriage 3 and the drive mechanism housing 4 move along the rack 5 and table 1 is carried along in this component direction the pressure rollers 19 and 20 couple the friction wheels 11 13 and 12 16 to each other via a resiliently loaded engagement both rollers 19 and 20 are mounted on a.