the derived series suffer from an inequality inherent in the nature of the experiment.
In the course of the experiment the skipping of more than 7 syllables was shown to be desirable, but I refrained from carrying that out. The investigations with the six 16-syllable series were carried quite far; and if series had been constructed using greater intervals, the breaks above mentioned would have had too much dominance. The derived series then contained ever fewer syllable-sequences for which an association was possible on the basis of the learning of the original arrangement; they were ever thus more incomparable.
The investigations were carried on as follows:—Each time the six series were learned in the original order and then 24 hours later in the derived and the times required were compared. On account of the limitation of the series to those described above the results are, under certain circumstances, open to a serious objection. Let it be supposed that the result is that the derived series are actually learned with a certain saving of time, then this saving is not necessarily due to the supposed cause, an association between syllables not immediately adjacent. The argument might, rather, run as follows. The syllables which are first learned in one order and after 24 hours in another are in both cases the same syllables. By means of the first learning they are impressed not merely in their definite order but also purely as individual syllables; with repetition they become to some extent familiar, at least more familiar than other syllables, which had not been learned just before. Moreover the new series have in part the same initial and final members as the old. Therefore, if they are learned in somewhat less time than the first series required, it is not to be wondered at. The basis of this does not necessarily lie in the artificial and systematic change of the arrangement, but it possibly rests merely on the identity of the syllables. If these were repeated on the second day in a new arrangement made entirely by chance they would probably show equally a saving in work.
In consideration of this objection and for the control of the remaining results I have introduced a further, the fifth, kind of derived series. The initial and final syllables of the original series were left in their places. The remaining 84 syllables, intermediates, were shaken up together and then, after chance
