2 and acts on a greater length of the yarn 1 creates a tension force 7 which is equal to the tension force 8 which is created by the oppositely directed greater portion of the jet of gas 3 and which is acting upon the shorter yarn length up to the sharp bend 6 in a variation of the embodiment of fig1 it is also possible that the jet of gas 3 impinge perpendicularly upon the yarn 1 fig3 and 4 show an apparatus intended for the execution the method a yarn guide body 9 having a channel 10 is arranged extending so far into the yarn path that the yarn 1 makes contact with the channel 10 at the base 13 and is deflected from its original path the yarn guide body 9 thereby assumes such a position that the bend 6 is located at the location where the yarn 1 runs onto the yarn guide body 9 and that the base 13 of the channel 10 is directed to the yarn motion direction 2 a nozzle 11 which is connected to a blower which is not illustrated having a diameter corresponding approximately to the width of the channel 10 is arranged such that its outlet opening 12 is directed against the yarn guide body 9 and is arranged exactly opposite to the channel 10 when a jet of gas 3 is directed by means of the nozzle 11 onto the yarn 1 there builds up an air damming zone in the channel 10 having a maximum directly under the jet of gas 3.