\Pro*por"tion*al\, a. [L. proportionalis: cf. F.
proportionnel.]
1. Having a due proportion, or comparative relation; being in
   suitable proportion or degree; as, the parts of an edifice
   are proportional. --Milton.
2. Relating to, or securing, proportion. --Hutton.
3. (Math.) Constituting a proportion; having the same, or a
   constant, ratio; as, proportional quantities; momentum is
   proportional to quantity of matter.
{Proportional logarithms}, logistic logarithms. See under
   {Logistic}.
{Proportional scale}, a scale on which are marked parts
   proportional to the logarithms of the natural numbers; a
   logarithmic scale.
{Proportional} {scales, compasses, dividers}, etc.
   (Draughting), instruments used in making copies of
   drawings, or drawings of objects, on an enlarged or
   reduced scale.

\Pro*por"tion*al\, n.
1. (Math.) Any number or quantity in a proportion; as, a mean
   proportional.
2. (Chem.) The combining weight or equivalent of an element.
   [Obs.]