intervals in the presence of an appreciation of the series as a rhythmical group.  The rhythmic integration of the stimuli is weakest when the intervals separating them are uniform, and since the question asked of the observer was invariably as to the apparent relative duration of the two intervals, it may well be conceived that the hearers lapsed from a rhythmical apprehension of the stimuli in these cases, and regarded the successive intervals in isolation from one another.  The illusions of judgment which appear in these experiences are essentially dependent on an apprehension of the series of sounds in the form of rhythmical groups.  So long as that attitude obtains it is absolutely impossible to make impartial comparison of the duration of successive intervals.  The group is a unit which cannot be analyzed while it continues to be apprehended as part of a rhythmical sequence.  We should expect to find, were observation possible, a solution of continuity in the rhythmical apprehension in every case in which these distortions of the normal rhythm form are forced on the attention.  This solution appears tardily.  If the observer be required to estimate critically the values of the successive intervals, the attention from the outset is turned away from the rhythmical grouping and directed on each interval as it appears.  When this attitude prevails very small differences in duration are recognized (e.g., those of 1.000:1.118, and 1.000:0.895).  But when this is not the case, the changes of relative duration, if not too great for the limits of adaptation, are absorbed by the rhythmical formula and pass unobserved, while variations which overstep these limits appear in consciousness only as the emergence of a new rhythmic figure.  Such inversions are not wholly restricted by the necessity of maintaining the coincidence of accentuation with objective stress.  With the relatively great differences involved in the present set of experiments, the rhythmical forms which appeared ignored often the objective accentuation of single groups and of longer series.  Thus, if the second interval of a dactyl were lengthened the unaccented element which preceded it received accentuation, while the actual stress on the first sound of the group passed unobserved; and in a complex series of twelve hammer-strokes the whole system of accentuation might be transposed in the hearer’s consciousness by variations in the duration of certain intervals, or even by simple increase or decrease in the rate of succession.[6]

   [6] Bolton found one subject apperceiving in four-beat groups a
   series of sounds in which increased stress fell only on every
   sixth.

In the experiments on dactylic rhythm the changes introduced affected the initial and final intervals only, the one being diminished in proportion as the other was increased, so that the total duration of the group remained constant.  The figures, arranged as in the preceding table, are given in Table L.