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The diffraction profile and its moments are obtained for particle-size broadening, the expressions being `exact' in the kinematic approximation for crystals of simple shapes (parallelepiped, tetrahedron, octahedron, sphere). A further term in the variance-range curve is obtained, depending on Mitra's parameter 34, for which the name `rotundity parameter' is proposed. The effect of a distribution of particle sizes is discussed; the Scherrer constant and the taper parameter are affected in a way already known, and M is unaffected.