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individual so that now and again the rate of succession of the terms 
corresponded little with the time required by the observer to spon- 
taneously take in the material presented. The difficulties arising 
from this, which are felt in individual psychological experiments 
much more strongly than in general investigations, do perhaps not 
render the results, achieved in this way, totally invalid. Neverthe- 
less, viewed more closely, they appear to me weighty enough to 
justify an intercomparison of the results obtained by the natural 
and the experimental method. 
The results reported in this paper have been obtained in a series 
of experiments performed in the Psychological Laboratory of the 
Utrecht Clinic for Psychiatry and Neurology. The course of the ex- 
periments was regulated as follows: 
Three observers (M, R and D) committed to memory 40 series of 
12 nonsense-syllables. For the first twenty (Group I) the observer 
was at liberty to choose his own rate of succession, to group the 
syllables, to determine the interval between two successive repeti- 
tions ete. all in his own way. The only restrictions he had to sub- 
mit to were that in the successive repetitions he was allowed to 
pronounce a syllable only once, and that when once his attention 
had averted from a syllable, it should on no account return to it 
again. The other 20 series (Group II) were exhibited by means 
of a mnemometer of our own construction. It consisted of a drum, 
rotating evenly and at a carefully tested speed about an horizontal 
axis by the help of a Heumuorz electromotor. On this drum was wound 
a strip of paper printed with the syllables at equal distances. Before 
the drum there was a screen with a slit in the centre past which 
the syllables flitted in succession when the drum was turned round. 
Thus the time of exposure was the same for each. syllable, so were 
the intervals between two successive syllables, so also were those 
between two successive repetitions. 
In the experiments of Group I as well as those of Group II the 
observer spoke through a voice-key, consisting of the diaphragm of 
a gramophone, to which a platinum disc had been attached. On this 
disc rested the platinum-covered point of a V-shaped arm, which 
was turning about an horizontal axis, and easily adjustable by the help 
of a sliding weight. The deflections of this arm broke the electric 
current flowing through the instrument even with the slightest 
intensity of the spoken sound on the diaphraghm. These breaks were 
registered by a marking magnet upon the drum of a kymographion. 
A second magnet drew a time-line (!/,‚ sec.) with the aid of 
KAGENAAR’S chronoscope. We were thus enabled to determine by the 
