Harmonic Range

A set of four Collinear points $A$, $B$, $C$, and $D$ arranged such that

$$AB:BC=2:1$$

$$AD:DC=6:3.$$

Hardy (1967) uses the term Harmonic System of Points to refer to a harmonic range.

See also Euler Line, Gergonne Line, Harmonic Conjugate Points, Soddy Line

References

Hardy, G. H. A Course of Pure Mathematics, 10th ed. Cambridge, England: Cambridge University Press, pp. 99 and 106, 1967.