FADING OF MEMORY-TRACES 533 



After the lapse of certain definite periods of time the series were 

 relearned, and the time (= t] -- t) necessary to relearn them was 

 also noted. Then the difference (= t) represented the time saved by 

 the previous repetitions, or in other words the time which would be 

 consumed in learning that proportion of syllables which was remem- 

 bered. The percentage - X 100 was employed by Ebbinghaus (and 



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has been employed by his successors in this field of investigation) as 

 the most convenient measure of the extent of forgetting. It is, of 

 course, not actually equivalent to the amount of memorized material 

 which has been forgotten, for the time required to memorize syllables 

 is, as we have seen, not proportional to their number. Nevertheless 

 the outline of the relationship between the time which has elapsed 

 since the material was learned and the amount of material forgotten 



is sufficiently clearly revealed by the successive values of - - X 100 



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noted by Ebbinghaus to show that this phenomenon, like that of 

 refreshment by sleep, occurs most rapidly in the beginning, when the 

 mass of deposit undergoing destruction or dispersal is greatest. The 

 following were the results obtained by Ebbinghaus the time being 

 reckoned from the end of the first period of learning to the end of the 

 second . 



Time in hours. - X 100 



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0.33 41.8 



1.00 . . 55.8 



8.80 . . . . . . .... 64.2 



24.00 66.3 



48.00 72.2 



144.00 74.6 



744.00 78.9 



The negative acceleration of this process is extraordinarily high, for 

 although over 55 per cent, of the time saved by the first period of 

 learning is lost in one hour, yet during the succeeding twenty-three 

 hours only 9 per cent, more is lost. In other words the Velocity of 

 Forgetting decreases very rapidly with the passage of time; it never, 

 under normal conditions, undergoes any increase in rapidity with time. 

 The process of forgetting is therefore essentially different in mechanism 

 from the process of memory-formation. 



It is very improbable that the fading of a memory-trace can be due 

 to chemical changes in the substance forming the trace, for no chemical 

 reactions are known which diminish so greatly in rapidity with time, 

 continue to proceed, and yet do not attain completion for such pro- 

 longed periods as the memory-traces persist. A reaction which was 55 

 per cent, completed in one hour would either have ceased before 

 twenty-four hours, or else would be much more than 66 per cent, com- 

 pleted. A chemical reaction, to display such extraordinary falling-off 



