opposing bearings 72b and 72c provides a loading effect to keep the window frame guide in its proper relationship to fixed guides 64a 64b similarly an air bearing 76a loads opposing air bearings 76b and 76c all mounted on side surfaces of the stage 10 in maintaining the proper location of stage 10 relative to the opposing window frame guide members 40b and 40d again in this case one air bearing such as 76a is gimbal mounted to provide a limited amount of misalignment or gimbal mounted with the gimbal on a flexure spring air bearings 72a 72b 72c and 76a 76b and 76c are conventional air bearings the outer structure 80 in fig1 is the base support structure for the fixed guides 46a 46b 64a 64b and the window frame guide members 40a 40d of the stage mechanism but does not support stage base structure 32 thus the underlying support is partitioned so the reaction force on base support structure 80 does not couple into the stage base structure 32 base support structure 80 is supported by its own support pillars or other conventional support elements not shown in this drawing to the ground i e the surface of the earth or the floor of a building an example of a suitable support structure is disclosed in above referenced u s patent application ser no 08 221 375 at fig1 b 1c this independent support structure for this portion of stage mechanism provides the above described advantage of transmitting the reaction forces of the reticle stage mechanism drive motors away from the frame supporting the other elements of the photolithography apparatus especially away from the optical elements including the projection lens and from the wafer stage thereby minimizing vibration.