counting the auxiliary motor is stopped by detecting a reference or 34 zero 34 position on the cam shaft in a variant the position of each envelope on the path may be detected by a series of cells analogous to the cell 41 and delivering appropriate control signals on the links 43 to 45 by means of a logic circuit the successive stages a closure for an envelope are illustrated in the diagrams fig2 a to 2e in which the components of the apparatus are designated by the same references as before and an envelope is given an overall reference 5 with its body being referenced 50 its flap 51 its foot 52 and its join or fold line between the flap and the body being referenced 53 these references 50 to 53 are not marked in all of the diagrams in order to avoid overcrowding them diagram 2a shows the stage during which the envelope 5 moves forwards or advances along the path 1 from the inlet 13 at which it was presented earlier and detected by the cell 41 the wheels 11a and 12a are driven in the direction of arrows 18a and advance the envelope along the path along arrow 58a as it advances the body 50 of the envelope passes footforemost through the moistening assembly 2 whose deflector is then in the rest position and through the folding and closing assembly whose presser rollers 30 and 31 are also in their rest position and then continues between the wheels 12a and 12b the flap 51 of the envelope still held between the wheels 11a and 11b is about to leave them as the envelope advances the cell 41 serves to detect successive positions of the envelope along.