from
The Collaborative International Dictionary of English v.0.48
Isomerism \I*som"er*ism\, n. (Chem.)
The state, quality, or relation, of two or more isomeric
substances.
[1913 Webster]
{Physical isomerism} (Chem.), a former term for {optical
isomerism}.
{optical isomerism} (Chem.), the condition or relation of
certain (isomeric) substances, which, while chemically
identical (in that they have the same composition, the
same molecular weights, and the same ultimate
constitution), are yet physically different, as in their
action on polarized light, as dextro- and l[ae]vo-tartaric
acids, or the sugars galactose and glucose. In such
compounds there is usually at least one unsymmetrical
carbon atom and typically more than one. See
{Unsymmetrical}.
[1913 Webster +PJC]