apparatus which may be used to carry out the procedure described with reference to fig3 and 4 the apparatus comprises a pair of main beams 50 and 51 interconnected by a pair of vertical hydraulic rams 52 the upper beam 50 carries three pair of arms 53 each arm being pivotally mounted on the beam 50 in each case the second arm of the pair is not shown for the sake of clarity the second arms are pivotally mounted on the opposite side of the beam 50 the lower end of each arm 53 has an inwardly directed hook formation which can engage on the underside of the rail head 3a of the rail 3 in the configuration illustrated in fig5 the apparatus is arranged to pull the center of the rail upwardly against reaction from two reaction pillars 54 inserted between the underside of the lower beam 51 and blocks 55 resting on the rail 3 the two outer pairs of arms 53a and 53c are held out of contact with the rail while the inner pair of arms 53b engage the rail head 3 and are pinned to the block 55 by means of a bolt or rod 56 passed therethrough a measuring bridge 57 is provided between the.