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Some Shapes

A particle described by its wavelength  \lambda and orbital radius  R may be classified by shape.

ShapeDefinition
a pointR = \lambda = 0
a line segment\lambda > R = 0
a plane sectionR > \lambda = 0
a plateR \gg \lambda > 0
a rod\lambda \gg R > 0
a cylinder\lambda \sim R > 0
Shapes are an important way of classifying experience as suggested by this French engraving of sea urchins.
Jean-Baptiste Lamarck, Echinus (detail) , Tableau Encyclopédique et Méthodique des Trois Règnes de la Nature, Paris 1791. Photograph by D Dunlop.