one of the more important, but missed ideas shown in wessel's "om directionens analytiske betegning" was vectors. wessel's main thing he wanted to show in the paper was not this, but he felt that the concept of numbers, with length and direction would be needed. wessel's thoughts on addition was: "two straight lines are added if we unite them in such a way that the second line begins where the first one ends and then pass a straight line from the first to the last point of the united lines. this line is the sum of the united lines". today, the same idea is used when adding vectors.