device shown in fig2 and 3a since the mode of operation of the rope pulling device of the arrangement of fig2 and 3a has been described herein above it is not necessary to disclose in detail the operation of the rope pulling device of the embodiment of fig4 6 when the drive aggregate 101 is set into operation and the drive shafts 102 and 103 rotate the wiper shaft 109 will be displaced in its oscillating movement by the oscillatory drive 110 111 and 112 simultaneously however the crank 114 also rotates and moves the driving rod 138 a reciprocal movement of the wiper blade 16 will now result from the action of the rope pulling drive whereas at the same time an oscillating movement will be imparted to the wiper blade via the wiper arm portions 132 124 as can be seen from fig1 the wiper arm 14 has its smallest length 56 fig3 and is in the operative position shown by solid line and should in the case of a greater pivoting angle u03b1 first enlarge its effective wiper length the greatest wiper length 50 must be reached when the wiper blade 16 is in the corner area of the windshield 10 then the portion 132 of the wiper arm must be moved in the opposite direction also along arrow 56 of fig3 unless the wiper.