The Greek mathematician Pythagoras made a key discovery about musical scales and octaves. He discovered that in stringed instruments, an octave was made with a 2 to 1 ratio of 2 strings being played. He also figured out how the other 7 notes were placed in between with an equal distance from each other. If you take a look at a harp, you will notice that there are some very long strings which sound very low, and then there are the little teeny tiny strings which make a very high pitched "pling" when they are plucked. If you take that low string and cut it in half, it would play the same pitch one octave higher, and if you were to take a string twice the size of the teeny tiny string, it would play the same pitch an octave lower. These musical principals discovered by Pythagoras seem to be very simple, but they were key in advancing our knowledge of music.