THE attention which J. D. Bernal¹ has directed to the importance of geometrical models for representing the structure of liquids has elicited considerable recent interest in the packing of spheres^{2â 7}. While previous investigations were often concerned with the dense random state^8,9, some of the more recent work has been devoted to looser states^3,4,6. Both Scott³ and MacRae and Gray⁴ obtained loose deposits of spheres by a rolling procedure, while Rutgers⁶, in common with Leva et al.¹⁰ some years earlier, obtained a loose packing by dumping or pouring. Porosities thus reported, though significantly higher than those found in the dense random state, are nevertheless still lower than those obtained either by rapidly inverting a cylinder¹¹ or by gradually diminishing to zero the gas (or liquid) flow through a fluidized bed^12,13. It is the latter porosities which correspond to those observed in both moving packed¹⁴ and incipiently fluidized¹³ beds.