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Elasticity
13
Abnormal piling implies any disarrangement which displaces the grains in the medium from their neighbours and so affects the gearing of the grains, as shown in models 4 and 5; in 4 the piling is approximately normal, the edges being free, while in 5 the piling is so abnormal as to prevent, entirely, the gearing in several lines.
The relative motion of the grains renders the medium elastic: and is thus the only cause of
Fig. 5.
