The ratio of two Rayleigh ratios for different angles of observation, i.e.
The angles must be specified; in light scattering
it is customary to let
and, most frequently,
PAC, 1983, 55, 931
(Definitions, terminology and symbols in colloid and surface chemistry. Part 1.14: Light scattering (Provisional))
on page 932
IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997). XML on-line corrected version: http://goldbook.iupac.org (2006-) created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8. doi:10.1351/goldbook