Ramsay
The ratio of 1:2 belongs to neither proximate nor differential periods. It corresponds to unity; and, like the square and the circle, it admits of no varieties. [Scientific Basis and Build of Music,page 106]

There are seven differential and eleven proximate periods all differing in their degrees of complexity according to the individual character of the ratio; and they illustrate to the eye what is the effect in the ear of the same ratios in the rapid region of the elastic vibrations which cause the musical sounds. [Scientific Basis and Build of Music,page 106]