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Mobility of medium
7. Mobility of the medium.
The singular surfaces, when their limited stability is overcome, are free to maintain their motions through the medium by a process of propagation in any direction—the number of grains forming up on the grains already in position being the same as those left behind; so that the grains in the nucleus have no mean motion whatever.
Any conception of this external propagation is difficult. But the process admits of such
Fig. 6.
