To produce an impression of rhythm, it is necessary to have a. Series of stimuli. These stimuli may be sounds, as in the case of poetry and music, muscular contractions, as in dancing and beat ing time, or lights and electrical shocks, as in some laboratory experiments. The stimuli which give the impression of rhythm, whatever their nature, may vary in intensity, in duration, and in quality, and may be separated by intervals of varying length. A fundamental task of the experimental investigation of rhythm is to investigate the part played by each of these factors. Only after each of them has been studied separately, may we study the effect when two or more of them are simultaneously involved, and when more complicated factors are introduced, as in melody and harmony.
