G. W. Slack

The behaviour of clusters of spheres falling in a viscous fluid Part 1. Experiment

B. J. Mason, K. Jayaweera, K. O. L. F. Jayaweera, 1964, Journal of Fluid Mechanics.

Sedimentation of a Large Number of Particles as a Cluster in Air

G. W. SLACK, G. W. Slack, 1963, Nature.