\begin{definition}[Definition:Intrinsic Equation/Whewell Equation]
A '''Whewell equation''' is an intrinsic equation for a curve $C$ such that $C$ is expressed in terms of its intrinsic properties:
:Arc length $s$
:Turning angle $\psi$
{{NamedforDef|William Whewell|cat = Whewell}}
\end{definition}