For the purposes of separating out the individual notes of a chord, it became necessary to symbolize the different notes in a way that could easily be understood without using symbols which are already commonly used in music today such as numbers and letters. It quickly became apparent that geometrical objects could be used to describe numbers. In other words, Circle, X, Triangle, Square = 1, 2, 3, 4.
Circle = 1 Continuous line, 1st Note
or Bass Note