An Experiment to Illustrate the Mode of Flow of a Viscous Fluid

Abstract

Now that the theory of glacier-movement propounded by James Forbes stands alone, undisturbed by conflicting hypotheses, we more readily perceive its simplicity and beauty; and we cannot refuse a tribute of admiration to the clarity of thought, no less to the skill in observation, which led that distinguished investigator to success in the treatment of a problem which his famous contemporaries had found so baffling. Whatever may be the ultimate explanation, there can be no question of the fact, that the ice of glaciers behaves precisely like a plastic solid or highly viscous liquid; and it is consequently by enquiries into the laws of viscous flow that we may justly seek to extend our knowledge of the movements of flowing ice. No substance is probably better suited for experiments in this direction than solid pitch, or that substance commonly known as ‘cobbler's wax,’ in which it occurs as the chief constituent. Under a sudden pull or pressure this material behaves like the most brittle solid, but when stress is slowly applied it yields continuously to deformation. A small fragment kneaded between the finger and thumb may be slowly drawn out into a thread of indefinite length, but if suddenly pulled it snaps across with a clean fracture; it may be readily impressed with the finger-nail, but a smart tap with the point of a needle shivers it into angular fragments. While it thus essentially resembles ice in the manner in which it reacts against deforming forces, it possesses the advantage