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Printed in Great Britain

FOREWORD

The ancients were of necessity interested in problems of flow, not merely of streams but of soft materials, such as clay and pitch. The potter came to recognise the essential difference between the viscous flow of pitch and the plastic Iow of clay, and upon Heraklitus there dawned the stimulating idea that “ everything flows.” Lucretius in his “ De Rerum Natura ” inąuired why it is that ohve oil is morę “ sluggish/' i.e., viscous, than winę, and proposes the entirely plausible hypothesis that the elements that go to make up the oil are either larger or else they are crooked and intertangled. From so promising an Overture much might have come down to us, but the Symphony remained unfinished.

An old trail of even the largest prey does not arouse the hounds like a fresh one, so the Science of Electricity arose and progressed amazingly, while the knowledge of the flow of matter, which to save circumlocution we now cali the Science of Rheology, seemed to lag behind. The flow of electricity may have seemed much morę mysterious and difAcult to measure than the flow of matter; but its very novelty attracted the adventurous Faraday a century ago and a host of others sińce. Just as Gladstone asked Faraday about this electricity, “ Of what use is it ? ” so one must be prepared to answer the same ąuestion about rheology ! Faraday said that before long a way might be found to tax