1. A method for automatic multi-layer welding of a joint (33) formed by two joint optical or mechanical sensor emitting signals representative of the contour of the joint in the current cross-section of the joint, which signals after evaluation control a deposition of the weld beads by means of a continuously fed electrode (32) which is directed towards a welding zone in the joint, said sensor being caused to measure points (41a-e, 42a-b) of the present contour of the joint in the current section which essentially define the cross-section of the joint and are positioned on the joint edges, the joint sides, and the joint bottom of the joint, the area (P.sub.pn) of a polygon determined by these measured points being calculated, a mean value (P.sub.pm) of said polygon areas being calculated, a mean amount of welding material per unit of length corresponding to the mean value of the polygon areas of the cross-section of the joint being determined, and the amount of welding material per unit of length for each cross-section of the joint being calculated as a function of the mean amount of welding material per unit of length and the ratio of the polygon area (P.sub.pn) of the cross-section of the joint to the mean value of the polygon areas (P.sub.pm), characterized in that the amount of welding material per unit of length is varied as a function of a current welding speed (V.sub.pn), with the welding speed (V.sub.pn) varying in a longitudinal direction of the joint, a set mean welding speed (P.sub.pm) being associated with the mean value of the polygon areas of the cross-sections of the joint and the welding speed (V.sub.pn) of each individual cross-section of the joint being calculated as a function of the mean welding speed and the ratio of the mean value (P.sub.pm) of the polygon areas to the polygon area (P.sub.pn) of the current cross-section of the joint, in that at least two weld beads (84, 85) are deposited in the joint to form an intermediate layer when the mean value of the values corresponding to the width of the joint in the various cross-sections of the joint at the level of said intermediate layer exceeds a set value, and in that the amount of welding material in the transverse direction of the joint is varied as a function of the current wire feed speed (V.sub.tXpn), the polygon determined by the measurement points being divided, in the latter case, by a vertical (87) through the joint in a first and a second part polygon (88, 89) comprising the measurement points on their respective one of the joint sides and the joint edges, the wire feed speed (V.sub.tXpn) for the weld beads to be deposited respectively on one and on the other joint side being determined with respect to each cross-section of the joint as a function of the current mean wire feed speed (V.sub.tpnm) and a relationship between the part polygon areas, the mean wire feed speed (V.sub.tpnm) for the various cross-sections of the joint being constant, i.e. the mean wire feed speed (V.sub.tpnm) does not vary in the lengthwise direction of the joint, whereby an even welding joint, filled to the level of its two joint edges, has an edge joint offset having an angle of inclination between an interconnection line of the joint edges and the horizontal plane exceeding 3.degree..