76 THE FOUNDATIONS OF SCIENCE 



but not colour ; others revive most vividly sounds, 

 tastes, or smells. To others the past scene is pre- 

 sented in words, either imagined as heard or as spoken 

 in their minds. Finally, some remember in imageless 

 thoughts. 



The simpler phenomena of memory have been 

 studied by measuring the number of repetitions 

 needed before a series of meaningless syllables 

 could be reproduced. The number requisite is found 

 to increase rapidly with the length of the series. 

 When, after a lapse of some time, they are partially 

 forgotten, new experiments may be made, and it is 

 now found that fewer repetitions are needed than at 

 first. By the elaboration of such experiments, the 

 effect of time, of new impressions, and of other com- 

 plications, may be investigated. 



Light may also thus be thrown on that most im- 

 portant property of our minds known as association. 

 If the syllables be learnt in pairs, the first one of each 

 pair being accented, they are easier to learn. Here 

 a second sensation, that of rhythm, is probably 

 introduced. Moreover, if one of the accented syllables 

 be exhibited afterwards, it is easier to recall the one 

 that follows than if the non-accented syllable be 

 exhibited. More complex associations are also found 

 between groups of several syllables ; while the greater 

 rapidity and completeness with which syllables are 

 learnt when they make sense, shows the effect of 

 association between sounds and meaning. The ad- 



