xliv Journal of Comparative Neurology. 



a unity among sounds is a regular temporal sequence within certain 

 limits, and perfect uniformity in intensity, pitch and quality. 



The conception of a rhythm demands a perfectly regular sequence 

 of impressions within the limits of about i.o sec and o.i sec. A 

 member of the sequence may contain one or more simple impressions. 

 If there are a number of impressions, they may stand in any order of 

 arrangement, or even in a state of confusion, but each member of the 

 sequence must be exactly the same in the arrangements of its 

 elements. H. H. Bawden. 



Conditions of Mental Activity. 1 



This paper gives the results of two lines of investigation carried 

 on at Clark University. 



Part i gives an account of experiments upon daily variations in 

 the rapidity of the repetition of old and of the formation of new as- 

 sociations, with a view to determine whether there is a natural 

 rhythm of mental activity or not. As showing the constant daily 

 variations, numerous tables of observations are given, indicating the 

 relative speed with which cards can be sorted, figures can be added 

 and multiplied, nonsense syllables memorized, etc. at various intervals 

 through the day. 



Among the results may be mentioned the following. The sub- 

 jects, whose records cover the entire waking period have a well 

 marked periodicity of mental activity. There is, however, no general 

 type of daily rhythm, and individual differences of the most striking 

 sort occur. The same influences have different effects upon different 

 individuals. Under the influence of fatigue, rest, and physical exer- 

 cise, the processes studied vary in the same direction. Statistical 

 investigations show that those who are engaged in mental work have 

 generally observed a daily rhythm of power. Actual measurements 

 and statistics of opinions both show that in a certain number of cases 

 there will be persons whose maximum activity comes at almost any 

 given hour of the waking period. The rhythm of activity may or may 

 not correspond with the actual energy at the person's disposal. Other 

 things being equal, the total amount which can be accomplished de- 

 creases as the interval since sleep increases, but the rate of work may 

 be most rapid a little before retiring. While most persons thus 

 recognize the existence of a daily periodicity of activity, which is of 



a BERGSTROEM, J. A. An Experimental Study of Some of the Conditions of 

 Mental Activity. Am. Jour, af Psychology, VI, 2, Jan., 94. 



