Abstract
The studies of Dewey and others indicating the existence of cycle synchronies (i.e., cycles observed in many, entirely different phenomena with the same cycle length and crests occurring at about the same time) suggest a common cause of a world wide or extra‐terrestrial nature. Also many rhythmic or fluctuating phenomena observed in mental processes in man and his behaviour patterns suggest similar world wide exogenous causes. Two possible causes are extensively discussed: (1) world wide geophysical changes in the atmosphere, probably due to solar influences which seem to affect both organic and inorganic colloids in living systems on earth and (2) fluctuations in gravity wave patterns in the universe.