Periodic Physico-Chemical Phenomena

Abstract

PERIODIC phenomena of all types have a peculiar fascination to the human mind, possibly because they suggest some of the processes of life. On the largest scale, mechanical periodicity is inherent in the movements of celestial bodies and of the earth, producing secondary periodicities, which we recognise as the yearly seasons, alternating day and night, the ebb and flow of the tides, and in other ways. These time-periodicities in their turn leave their mark on earthly structures which are in the course of formation, producing spatial periodicities, such as the annual rings in the trunks of trees, and probably the bands in many geological deposits. The seismologist and the meteorologist recognise periodicities in earthquakes, in thunderstorms and other climatic conditions, but periodicity is above all familiar to the biologist. To consider the processes of breathing and the heart-beat is sufficient to indicate the fundamental importance of periodic phenomena in biological systems, quite apart from the interest attached to structures having a spatial periodicity. In fact, periodicity both in space and in time has so come to be regarded as a characteristic of the biological sciences that when it is encountered in purely physical systems it almost constitutes a link between the two.