1Table 2 is available in the online version of this article and from the IUCr electronic archives (Reference: HW0085 ). Services for accessing these data are described at the back of the journal.
2D[4,3] =
Vidi/
Vi, where Vi is the relative volume in group i and di is the mean group diameter.
3Figs. 8 to 15 are available in the online version of this article and from the IUCr electronic archives (Reference: HW0085) . Services for accessing these data are described at the back of the journal.